blank iec form - ulstandards.ul.com...178 between any iec publication and the corresponding national...
TRANSCRIPT
– 2 – IEC TR 62368-2:2019 © IEC 2019
CONTENTS 1
FOREWORD ........................................................................................................................... 6 2
INTRODUCTION ..................................................................................................................... 9 3
0 Principles of this product safety standard ....................................................................... 10 4
1 Scope ............................................................................................................................ 13 5
2 Normative references ..................................................................................................... 13 6
3 Terms, definitions and abbreviations .............................................................................. 13 7
4 General requirements .................................................................................................... 16 8
5 Electrically-caused injury ............................................................................................... 23 9
6 Electrically-caused fire ................................................................................................... 70 10
7 Injury caused by hazardous substances ....................................................................... 105 11
8 Mechanically-caused injury .......................................................................................... 109 12
9 Thermal burn injury ...................................................................................................... 117 13
10 Radiation ..................................................................................................................... 127 14
Annex A Examples of equipment within the scope of this standard ................................. 134 15
Annex B Normal operating condition tests, abnormal operating condition tests and 16
single fault condit ion tests ................................................................................ 134 17
Annex C UV Radiation .................................................................................................... 137 18
Annex D Test generators ................................................................................................ 137 19
Annex E Test conditions for equipment containing audio amplifiers ................................ 138 20
Annex F Equipment markings, instructions, and instructional safeguards ........................ 138 21
Annex G Components ..................................................................................................... 139 22
Annex H Criteria for telephone ringing signals ................................................................ 147 23
Annex J Insulated winding wires for use without interleaved insulation ........................... 149 24
Annex K Safety interlocks ............................................................................................... 149 25
Annex L Disconnect devices ........................................................................................... 149 26
Annex M Equipment containing batteries and their protection circuits .............................. 150 27
Annex O Measurement of creepage distances and clearances ........................................ 159 28
Annex P Safeguards against conductive objects ............................................................. 160 29
Annex Q Circuits intended for interconnection with building wiring .................................. 161 30
Annex R Limited short-circuit test ................................................................................... 161 31
Annex S Tests for resistance to heat and fire .................................................................. 162 32
Annex T Mechanical strength tests ................................................................................. 163 33
Annex U Mechanical strength of CRTs and protection against the effects of 34
implosion .......................................................................................................... 164 35
Annex V Determination of accessible parts ..................................................................... 165 36
Annex X Alternative method for determing clearances for insulation in circuits 37
connected to an AC mains not exceeding 420 V peak (300 V RMS) .................. 165 38
Annex Y Construction requirements for outdoor enclosures ............................................ 166 39
Annex A (informative) Background information related to the use of SPDs ......................... 169 40
Annex B (informative) Background information related to measurement of discharges 41
– Determining the R-C discharge time constant for X- and Y-capacitors .............................. 182 42
Annex C (informative) Background information related to resistance to candle flame 43
ignition ................................................................................................................................ 194 44
IEC TR 62368-2:2019 © IEC 2019 – 3 –
Bibliography ........................................................................................................................ 195 45
46
Figure 1 – Risk reduction as given in ISO/IEC Guide 51 ........................................................ 11 47
Figure 2 – HBSE Process Chart ............................................................................................ 12 48
Figure 3 – Protective bonding conductor as part of a safeguard ............................................ 15 49
Figure 4 – Safeguards for protecting an ordinary person ....................................................... 19 50
Figure 5 – Safeguards for protecting an instructed person .................................................... 20 51
Figure 6 – Safeguards for protecting a skilled person ............................................................ 20 52
Figure 7 – Flow chart showing the intent of the glass requirements ....................................... 22 53
Figure 8 – Conventional time/current zones of effects of AC currents (15 Hz to 100 Hz) 54
on persons for a current path corresponding to left hand to feet (see IEC/TS 60479 -55
1:2005, Figure 20) ................................................................................................................ 25 56
Figure 9 – Conventional time/current zones of effects of DC currents on persons for a 57
longitudinal upward current path (see IEC/TS 60479-1:2005, Figure 22) ............................... 26 58
Figure 10 – Illustration that limits depend on both voltage and current .................................. 27 59
Figure 11 – Illustration of working voltage ............................................................................. 39 60
Figure 12 – Illustration of transient voltages on paired conductor external circuits ................ 41 61
Figure 13 – Illustration of transient voltages on coaxial -cable external circuits ...................... 42 62
Figure 14 – Basic and reinforced insulation in Table 14 of IEC 62368-1:2018; ratio 63
reinforced to basic ................................................................................................................ 43 64
Figure 15 – Reinforced clearances according to Rule 1, Rule 2, and Table 14 ...................... 45 65
Figure 16 – Example illustrating accessible internal wi ring .................................................... 53 66
Figure 17 – Waveform on insulation without surge suppressors and no breakdown ............... 56 67
Figure 18 – Waveforms on insulation dur ing breakdown without surge suppressors .............. 57 68
Figure 19 – Waveforms on insulation with surge suppressors in operation ............................ 57 69
Figure 20 – Waveform on short-circuited surge suppressor and insulation ............................ 57 70
Figure 21 – Example for an ES2 source ................................................................................ 59 71
Figure 22 – Example for an ES3 source ................................................................................ 59 72
Figure 23 – Overview of protective conductors ...................................................................... 62 73
Figure 24 – Example of a typical touch current measuring net work ....................................... 64 74
Figure 25 – Touch current from a floating circuit ................................................................... 67 75
Figure 26 – Touch current from an earthed circuit ................................................................. 67 76
Figure 27 – Summation of touch currents in a PABX ............................................................. 68 77
Figure 28 – Possible safeguards against electrically -caused fire ........................................... 75 78
Figure 29 – Fire clause flow chart ......................................................................................... 78 79
Figure 30 – Prevent ignition flow chart .................................................................................. 83 80
Figure 31 – Control fire spread summary .............................................................................. 85 81
Figure 32 – Control fire spread PS2 ...................................................................................... 86 82
Figure 33 – Control fire spread PS3 ...................................................................................... 87 83
Figure 34 – Fire cone application to a large component ........................................................ 96 84
Figure 35 – Flowchart demonstrating the hierarchy of hazard management ........................ 108 85
Figure 36 – Model for chemical injury .................................................................................. 109 86
Figure 37 – Direction of forces to be applied ....................................................................... 114 87
Figure 38 – Model for a burn injury ..................................................................................... 117 88
– 4 – IEC TR 62368-2:2019 © IEC 2019
Figure 39 – Model for safeguards against thermal burn injury ............................................. 119 89
Figure 40 – Model for absence of a thermal hazard ............................................................. 120 90
Figure 41 – Model for presence of a thermal hazard with a physical safeguard in place ...... 120 91
Figure 42 – Model for presence of a thermal hazard with behavioural safeguard 92
in place ............................................................................................................................... 120 93
Figure 43 – Flowchart for evaluation of Image projectors (beamers) ................................... 129 94
Figure 44 – Graphical representation of LAeq,T .................................................................. 131 95
Figure 45 – Overview of operating modes ........................................................................... 136 96
Figure 46 – Voltage-current characteristics (Typical data) ................................................... 141 97
Figure 47 – Example of IC current limiter circuit .................................................................. 145 98
Figure 48 – Current limit curves .......................................................................................... 148 99
Figure 49 – Example of a dummy battery circuit .................................................................. 158 100
Figure 50 – Example of a circuit with two power sources..................................................... 161 101
Figure A.1 – Installation has poor earthing and bonding; equipment damaged 102
(from ITU-T K.66) ................................................................................................................ 170 103
Figure A.2 – Installation has poor earthing and bonding; using main earth bar for 104
protection against lightning strike (from ITU -T K.66) ........................................................... 170 105
Figure A.3 – Installation with poor earthing and bonding, using a varistor and a GDT 106
for protection against a lightning strike ................................................................................ 171 107
Figure A.4 – Installation with poor earthing and bonding; equipment damaged (TV set) ...... 171 108
Figure A.5 – Safeguards ..................................................................................................... 172 109
Figure A.6 – Discharge stages ............................................................................................ 176 110
Figure A.7 – Holdover ......................................................................................................... 177 111
Figure A.8 – Discharge ....................................................................................................... 178 112
Figure A.9 – Characteristics ................................................................................................ 179 113
Figure A.10 – Follow on current pictures ............................................................................. 180 114
Figure B.1 – Typical EMC filter schematic ........................................................................... 182 115
Figure B.2 – 100 M oscilloscope probes ........................................................................... 184 116
Figure B.3 – Combinations of EUT resistance and capacitance for 1 -s time constant .......... 186 117
Figure B.4 – 240 V mains followed by capacitor discharge .................................................. 188 118
Figure B.5 – Time constant measurement schematic .......................................................... 189 119
Figure B.6 – Worst-case measured time constant values for 100 M and 10 M probes .... 193 120
121
Table 1 – General summary of required safeguards .............................................................. 20 122
Table 2 – Time/current zones for AC 15 Hz to 100 Hz for hand to feet pathway (see 123
IEC/TS 60479-1:2005, Table 11) ........................................................................................... 26 124
Table 3 – Time/current zones for DC for hand to feet pathway (see IEC/TS 60479 -125
1:2005, Table 13).................................................................................................................. 27 126
Table 4 – Limit values of accessible capacitance (threshold of pain) ..................................... 30 127
Table 5 – Total body resistances RT for a current path hand to hand, DC, for large 128
surface areas of contact in dry condition ............................................................................... 32 129
Table 6 – Insulation requirements for external circuits .......................................................... 42 130
Table 7 – Voltage drop across clearance and solid insulation in series ................................. 47 131
Table 8 – Examples of application of various safeguards ...................................................... 77 132
IEC TR 62368-2:2019 © IEC 2019 – 5 –
Table 9 – Basic safeguards against fire under normal operating conditions and 133
abnormal operating conditions .............................................................................................. 79 134
Table 10 – Supplementary safeguards against fire under single faul t conditions ................... 80 135
Table 11 – Method 1: Reduce the likelihood of ignition ......................................................... 82 136
Table 12 – Method 2: Control fire spread .............................................................................. 91 137
Table 13 – Fire barrier and fire enclosure flammability requirements ..................................... 98 138
Table 14 – Summary – Fire enclosure and fire barrier material requ irements ...................... 102 139
Table 15 – Control of chemical hazards .............................................................................. 107 140
Table 16 – Overview of requirements for dose-based systems ............................................ 133 141
Table 17 – Safety of batteries and their cells – requirements (expanded information on 142
documents and scope) ........................................................................................................ 152 143
Table B.1 – 100- M oscilloscope probes ........................................................................... 184 144
Table B.2 – Capacitor discharge ......................................................................................... 185 145
Table B.3 – Maximum Tmeasured values for combinations of REUT and CEUT for 146
TEUT of 1 s ........................................................................................................................ 192 147
148
149
– 6 – IEC TR 62368-2:2019 © IEC 2019
INTERNATIONAL ELECTROTECHNICAL COMMISSION 150
____________ 151
152
AUDIO/VIDEO, INFORMATION AND 153
COMMUNICATION TECHNOLOGY EQUIPMENT – 154
155
Part 2: Explanatory information related to IEC 62368-1:2018 156
157
FOREWORD 158
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising 159 all national electrotechnical committees (IEC National Committees). The object of IEC is to promote 160 international co-operation on all questions concer ning standardization in the electrical and electronic fields. To 161 this end and in addition to other activities, IEC publishes International Standards, Technical Specifications, 162 Technical Reports, Publicly Available Specifications (PAS) and Guides (hereafter referred to as “IEC 163 Publication(s)”). Their preparation is entrusted to technical committees; any IEC National Committee interested 164 in the subject dealt with may participate in this preparatory work. International, governmental and non -165 governmental organizations liaising with the IEC also participate in this preparation. IEC collaborates closely 166 with the International Organization for Standardization (ISO) in accordance with conditions determined by 167 agreement between the two organizations. 168
2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international 169 consensus of opinion on the relevant subjects since each technical committee has representation from all 170 interested IEC National Committees. 171
3) IEC Publicat ions have the form of recommendations for international use and are accepted by IEC National 172 Committees in that sense. While all reasonable efforts are made to ensure that the technical content of IEC 173 Publications is accurate, IEC cannot be held responsibl e for the way in which they are used or for any 174 misinterpretation by any end user. 175
4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications 176 transparently to the maximum extent possible in their national a nd regional publications. Any divergence 177 between any IEC Publication and the corresponding national or regional publication shall be clearly indicated in 178 the latter. 179
5) IEC itself does not provide any attestation of conformity. Independent certification bo dies provide conformity 180 assessment services and, in some areas, access to IEC marks of conformity. IEC is not responsible for any 181 services carried out by independent certification bodies. 182
6) All users should ensure that they have the latest edition of this publication. 183
7) No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and 184 members of its technical committees and IEC National Committees for any personal injury, property damage or 185 other damage of any nature whatsoever, whether direct or indirect, or for costs (including legal fees) and 186 expenses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC 187 Publications. 188
8) Attention is drawn to the Normative referen ces cited in this publication. Use of the referenced publications is 189 indispensable for the correct application of this publication. 190
9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of 191 patent rights. IEC shall not be held responsible for identifying any or all such patent rights. 192
The main task of IEC technical committees is to prepare International Standards. However, a 193
technical committee may propose the publication of a technical report when it h as collected 194
data of a different kind from that which is normally published as an International Standard, for 195
example, "state of the art". 196
IEC 62368-2, which is a Technical Report, has been prepared by IEC technical committee 197
TC 108: Safety of electronic equipment within the field of audio/video, information technology 198
and communication technology. 199
This third edition updates the second edition of IEC 62368-2 published in 2014 to take into 200
account changes made to IEC 62368-1:2014 as identified in the Foreword of 201
IEC 62368-1:2018. 202
This Technical Report is informative only. In case of a conflict between IEC 62368-1 and IEC 203
TR 62368-2, the requirements in IEC 62368-1 prevail over this Technical Report. 204
IEC TR 62368-2:2019 © IEC 2019 – 7 –
The text of this technical report is based on the following documents: 205
Enquiry draft Report on voting
108/708/DTR 108/711/RVDTR
206
Full information on the voting for the approval of this technical report can be found in the 207
report on voting indicated in the above table. 208
In this document, the following print types are used: 209
– notes/explanatory matter: in smaller roman type; 210
– tables and figures that are included in the rationale have linked fields (shaded in grey if 211
“field shading” is active); 212
– terms that are defined in IEC 62368-1: in bold type. 213
In this document, where the term (HBSDT) is used, it stands for Hazard Based Standard 214
Development Team, which is the Working Group of IEC TC 108 responsible for the 215
development and maintenance of IEC 62368-1. 216
This publication has been drafted in accordance with the ISO/IEC Direct ives, Part 2. 217
A list of all parts of the IEC 62368 series can be found, under the general title Audio/video, 218
information and communication technology equipment , on the IEC website. 219
In this document, only those subclauses from IEC 62368-1 considered to need further 220
background reference information or explanation to benefit the reader in applying the relevant 221
requirements are included. Therefore, not all numbered subclauses are cited. Unless 222
otherwise noted, all references are to clauses, subclauses, annexes, figures or tables located 223
in IEC 62368-1:2018. 224
The entries in the document may have one or two of the following subheadings in addition to 225
the Rationale statement: 226
Source – where the source is known and is a document that is accessible to the general 227
public, a reference is provided. 228
Purpose – where there is a need and when it may prove helpful to the understanding of the 229
Rationale, we have added a Purpose statement. 230
231
– 8 – IEC TR 62368-2:2019 © IEC 2019
The committee has decided that the contents of this publication will remain unchanged u ntil 232
the stability date indicated on the IEC web site under "http://webstore.iec.ch" in the data 233
related to the specific publication. At this date, the publication will be 234
• reconfirmed, 235
• withdrawn, 236
• replaced by a revised edition, or 237
• amended. 238
239
IMPORTANT – The 'colour inside' logo on the cover page of this publication indicates that it contains colours which are considered to be useful for the correct understanding of its contents. Users should therefore print this document using a colour printer.
240
241
IEC TR 62368-2:2019 © IEC 2019 – 9 –
INTRODUCTION 242
IEC 62368-1 is based on the principles of hazard -based safety engineering, which is a 243
different way of developing and specifying safety considerations than that of the current 244
practice. While this document is different from traditional IEC safety docume nts in its 245
approach and while it is believed that IEC 62368-1 provides a number of advantages, its 246
introduction and evolution are not intended to result in significant changes to the existing 247
safety philosophy that led to the development of the safety requ irements contained in 248
IEC 60065 and IEC 60950-1. The predominant reason behind the creation of IEC 62368-1 is 249
to simplify the problems created by the merging of the technologies of ITE and CE. The 250
techniques used are novel, so a learning process is require d and experience is needed in its 251
application. Consequently, the committee recommends that this edition of the document be 252
considered as an alternative to IEC 60065 or IEC 60950-1 at least over the recommended 253
transition period. 254
255
256
– 10 – IEC TR 62368-2:2019 © IEC 2019
AUDIO/VIDEO, INFORMATION AND 257
COMMUNICATION TECHNOLOGY EQUIPMENT – 258
259
Part 2: Explanatory information related to IEC 62368-1:2018 260
261
262
263
0 Principles of this product safety standard 264
Clause 0 is informational and provides a rationale for the normative clauses 265
of the document. 266
0.5.1 General 267
ISO/IEC Guide 51:2014, 6.3.5 states: 268
“When reducing risks the order of priority shall be as follows: 269
a) inherently safe design; 270
b) guards and protective devices; 271
c) information for end users. 272
Inherently safe design measures are the first and most imp ortant step in 273
the risk reduction process. This is because protective measures inherent to 274
the characteristics of the product or system are likely to remain effective, 275
whereas experience has shown that even well -designed guards and 276
protective devices can fail or be violated and information for use might not 277
be followed. 278
Guards and protective devices shall be used whenever an inherently safe 279
design measure does not reasonably make it possible either to remove 280
hazards or to sufficiently reduce risks. Compleme ntary protective measures 281
involving additional equipment (for example, emergency stop equipment) 282
might have to be implemented. 283
The end user has a role to play in the risk reduction procedure by 284
complying with the information provided by the designer/suppli er. However, 285
information for use shall not be a substitute for the correct application of 286
inherently safe design measures, guards or complementary protective 287
measures.” 288
In general, this principle is used in IEC 62368-1. The table below shows a 289
comparison between the hierarchy required in ISO/IEC Guide 51 and the 290
hierarchy used in IEC 62368-1:2018: 291
ISO/IEC Guide 51 IEC 62368-1
a) inherently safe design 1. inherently safe design by limiting all energy hazards to class 1
b) guards and protective devices 2. equipment safeguards
3. installation safeguards
4. personal safeguards
c) information for end users 5. behavioral safeguards
6. instructional safeguards
292
Risk assessment has been considered as part of the development of 293
IEC 62368-1 as indicated in the following from ISO/IEC Guide 51 (Figure 1) 294
in this document. See also the Hazard Based Safety Engineering (HBSE) 295
Process Flow (Figure 2) in this document that also provides additional 296
details for the above comparison. 297
IEC TR 62368-2:2019 © IEC 2019 – 11 –
298
Figure 1 – Risk reduction as given in ISO/IEC Guide 51 299
– 12 – IEC TR 62368-2:2019 © IEC 2019
300
301
Figure 2 – HBSE Process Chart 302
0.5.7 Equipment safeguards during skilled person service conditions 303
Purpose: To explain the intent of requirements for providing safeguards against 304
involuntary reaction. 305
Rationale: By definition, a skilled person has the education and experience to identify 306
all class 3 energy sources to which he may be exposed. However, while 307
servicing one class 3 energy source in one location, a skilled person may 308
be exposed to another class 3 energy source in a different location. 309
In such a situation, either of two events is possible. First, something may 310
cause an involuntary reaction of the skilled person with the consequences 311
of contact with the class 3 energy source in the different location. Second, 312
the space in which the skilled person is located may be small and 313
cramped, and inadvertent contact with a class 3 energy source in the 314
different location may be likely. 315
In such situations, this document may require an equipment safeguard 316
solely for the protection of a skilled person while performing servicing 317
activity. 318
0.10 Thermally-caused injury (skin burn) 319
Purpose: The requirements basically address safeguards against thermal energy 320
transfer by conduction. They do not specifically address safeguards 321
against thermal energy transfer by convection or radiation. However, as the 322
temperatures from hot surfaces due to conduction are always higher than 323
the radiated or convected temperatures, these are considered to be 324
covered by the requirements against conducted energy transfer. 325
___________ 326
Met opmerkingen [RJ1]: See Brussels item 6.2.15
IEC TR 62368-2:2019 © IEC 2019 – 13 –
1 Scope 327
Purpose: To identify the purpose and applicability of this document and the 328
exclusions from the scope. 329
Rationale: The scope excludes requirements for functional safety. Functional safety is 330
addressed in IEC 61508-1. Because the scope includes computers that 331
may control safety systems, functional safety requirements would 332
necessarily include requirements for computer processes and software. 333
The requirements provided in IEC 60950-23 could be modified and added 334
to IEC 62368 as another –X document. However, because of the hazard-335
based nature of IEC 62368-1, the requirements from IEC 60950-23 have 336
been incorporated into the body of IEC 62368-1 and made more generic. 337
The intent of the addition of the IEC 60950-23 requirements is to maintain 338
the overall intent of the technical requirements from IEC 60950-23, 339
incorporate them into IEC 62368-1 following the overall format of 340
IEC 62368-1 and simplify and facilitate the application of these 341
requirements. 342
Robots traditionally are covered under the scopes of ISO documents, 343
typically maintained by ISO TC 299. ISO TC 299 has working groups for 344
personal care robots and service robots, and produces fo r example, 345
ISO 13482, Robots and robotic devices – Safety requirements for personal 346
care robots. 347
___________ 348
2 Normative references 349
The list of normative references is a list of all documents that have a 350
normative reference to it in the body of the document. As such, referenced 351
documents are indispensable for the application of this document. For 352
dated references, only the edition cited applies. For undated references, 353
the latest edition of the referenced document (including any amendments) 354
applies. 355
Recently, there were some issues with test houses that wanted to use the 356
latest edition as soon as it was published. As this creates serious problems 357
for manufacturers, since they have no chance to prepare, it was felt that a 358
reasonable transition period should be taken into account. This is in line 359
with earlier decisions taken by the SMB that allow transition periods to be 360
mentioned in the foreword of the documents. Therefore IEC TC 108 361
decided to indicate this in the introduction of the normative references 362
clause, to instruct test houses to take into account any transition period, 363
effective date or date of withdrawal established for the document. 364
These documents are referenced, in whole, in part , or as alternative 365
requirements to the requirements contained in thi s document. Their use is 366
specified, where necessary, for the application of the requirements of this 367
document. The fact that a standard is mentioned in the list does not mean 368
that compliance with the document or parts of it are required. 369
___________ 370
3 Terms, definitions and abbreviations 371
Rationale is provided for definitions that deviate from IEV definitions or 372
from Basic or Group Safety publication definitions. 373
3.3.2.1 electrical enclosure 374
Source: IEC 60050-195:1998, 195-06-13 375
– 14 – IEC TR 62368-2:2019 © IEC 2019
Purpose: To support the concept of safeguards as used in this document. 376
Rationale: The IEV definition is modified to use the term “safeguard” in place of the 377
word “protection”. The word “safeguard” identifies a physical “thing” 378
whereas the word “protection” identifies the act of prote cting. This 379
document sets forth requirements for use of physical safeguards and 380
requirements for those safeguards. The safeguards provide “protection” 381
against injury from the equipment. 382
3.3.5.1 basic insulation 383
Source: IEC 60050-195:1998, 195-06-06 384
Purpose: To support the concept of safeguards as used in this document. 385
Rationale: The IEV definition is modified to use the term “safeguard” in place of the 386
word “protection” . The word “safeguard” identifies a physical “thing” 387
whereas the word “protection” identifies the act of protecting. This 388
document sets forth requirements for use of physical safeguards and 389
requirements for those safeguards. The safeguards provide “protection” 390
against injury from the equipment. 391
3.3.5.2 double insulation 392
Source: IEC 60050-195:1998, 195-06-08 393
Purpose: To support the concept of safeguards as used in this document. 394
Rationale: See 3.3.5.1, basic insulation. 395
3.3.5.6 solid insulation 396
Source: IEC 60050-212:2015, 212-11-02 397
3.3.5.7 supplementary insulation 398
Source: IEC 60050-195:1998, 195-06-07 399
Purpose: To support the concept of safeguards as used in this document. 400
Rationale: See 3.3.5.1, basic insulation. 401
3.3.6.9 restricted access area 402
Source: IEC 60050-195:1998, 195-04-04 403
Purpose: To use the concept of “ instructed persons” and “skilled persons” as used 404
in this document. 405
Rationale: The IEV definition is modified to use the terms “ instructed persons” and 406
“skilled persons” rather than “electrically instructed persons” and 407
“electrically skilled persons.” 408
3.3.7.7 reasonably foreseeable misuse 409
Source: ISO/IEC Guide 51:2014, 3.7 410
Rationale: Misuse depends on personal objectives, personal perception of the 411
equipment, and the possible use of the equipment (in a manner not 412
intended by the manufacturer) to accomplish those personal objectives. 413
Equipment within the scope of this document ranges from small handheld 414
equipment to large, permanently installed equipment. There is no 415
commonality among the equipment for readily predicting human behaviour 416
leading to misuse of the equipment and resultant injury. Where a possible 417
reasonably foreseeable misuse that may lead to an injury is not covered 418
by the requirements of the document, manufacturers are encouraged to 419
consider reasonably foreseeable misuse of equipment and provide 420
safeguards, as applicable, to prevent injury in the event of such misuse . 421
(Not all reasonably foreseeable misuse of equipment results in injury or 422
potential for injury.) 423
IEC TR 62368-2:2019 © IEC 2019 – 15 –
3.3.8.1 instructed person 424
Source: IEC 60050-826:2004, 826-18-02 425
Rationale: The IEV definition is modified to use the terms “energy sources”, “skilled 426
person”, and “precautionary safeguard ”. The definition is made stronger 427
by using the term “instructed” rather than “advised”. 428
3.3.8.3 skilled person 429
Source: IEC 60050-826:2004, 826-18-01 430
Rationale: The IEV definition is modified to use the phrase “to reduce the likelihood 431
of”. IEC 62368-1, in general, tends not use the word “hazard”. 432
3.3.11.9 protective bonding conductor 433
Rationale: The protective bonding conductor, is not a complete safeguard, but a 434
component part of the earthing system safeguard. The protective 435
bonding conductor provides a fault current pathway from a part (insulated 436
from ES3 by basic insulation only) to the equipment protective earthing 437
terminal, see Figure 3 in this document. 438
439
Figure 3 – Protective bonding conductor as part of a safeguard 440
The parts required to be earthed via a protective bonding conductor are 441
those that have only basic insulation between the parts and ES3, and are 442
connected to accessible parts. 443
Only the fault current pathway is required to be a protective bonding 444
conductor. Other earthing connections of accessible conductive parts 445
can be by means of a functional earth conductor to the equipment PE 446
terminal or to a protective bonding conductor. 447
3.3.14.3 prospective touch voltage 448
Source: IEC 60050-195:1998, 195-05-09 449
Purpose: To properly identify electric shock energy source voltages. 450
Rationale: The IEV definition is modified to delete “animal”. The word “pers on” is also 451
deleted as all of the requirements in the document are with respect to 452
persons. 453
3.3.14.8 working voltage 454
Source: IEC 60664-1:2007, 3.5 455
Purpose: To distinguish between RMS. working voltage and the peak of the 456
working voltage. 457
– 16 – IEC TR 62368-2:2019 © IEC 2019
Rationale: The IEC 60664-1 definition is modified to delete “RMS”. IEC 62368-1 uses 458
both RMS. working voltage and peak of the working voltage; each term 459
is defined. 460
3.3.15.2 class II construction 461
Source: IEC 60335-1:2010, 3.3.11 462
Purpose: Although the term is not used in t he document, for completeness, it was 463
decided to retain this definition. 464
Rationale: The word “appliance” is changed to “equipment”. 465
____________ 466
4 General requirements 467
Purpose: To explain how to investigate and determine whether or not safety is 468
involved. 469
Rationale: In order to establish whether or not safety is involved, the circuits and 470
construction are investigated to determine whether the consequences of 471
possible fault conditions would lead to an injury. Safety is involved if, as a 472
result of a single fault condition, the consequences of the fault lead to a 473
risk of injury. 474
If a fault condition should lead to a risk of injury, the part, material, or 475
device whose fault was simulated may comprise a safeguard. 476
Rationale is provided for questions regarding the omission of some 477
traditional requirements appearing in other safety documents. Rationale is 478
also provided for further explanation of new concepts and requirements in 479
this document. 480
Reasonable foreseeable misuse 481
Rationale: Apart from Annex M, this document does not specifically mention 482
foreseeable misuse or abnormal operating conditions . Nevertheless, the 483
requirements of the document cover many kinds of foreseeable misuse, 484
such as covering of ventilation openings, paper jams, stalled motors, etc. 485
functional insulation 486
Rationale: This documentdoes not include requirements for functional insulation . By 487
its nature, functional insulation does not provide a safeguard function 488
against electric shock or electrically-caused fire and therefore may be 489
faulted. Obviously, not all functional insulations are faulted as this would 490
be prohibitively time-consuming. Sites for functional insulation faults 491
should be based upon physical examination of the equipment, and upon the 492
electrical schematic. 493
Note that basic insulation and reinforced insulation may also serve as 494
functional insulation , in which case the insulation is not faulted. 495
IEC TR 62368-2:2019 © IEC 2019 – 17 –
functional components 496
Rationale: This document does not include requirements for functional components. 497
By their nature, individual functional components do not provide a 498
safeguard function against electric shock, electrically -caused fire, thermal 499
injury, etc., and therefore may be candidates for fault testing. Obviously, 500
not all functional components are faulted as this would be prohibitively 501
time-consuming. Candidate components for fault testing should be based 502
upon physical examination of the equipment, upon the electrical schematic 503
diagrams, and whether a fault of that component might result in conditions 504
for electric shock, conditions for ignition and propagation of fire, conditions 505
for thermal injury, etc. 506
As with all single fault condition testing (Clause B.4), upon faulting of a 507
functional component, there shall not be any safety consequence (for 508
example, a benign consequence), or a basic safeguard, supplementary 509
safeguard , or reinforced safeguard shall remain effective. 510
In some cases, a pair of components may comprise a safeguard. If the 511
fault of one of the components in the pair is mitigated by the second 512
component, then the pair is designated as a double safeguard. For 513
example, if two diodes are employed in series to protect a battery from 514
reverse charge, then the pair comprises a double safeguard and the 515
components should be limited to the manufacturer and part number actually 516
tested. A second example is that of an X-capacitor and discharge resistor. 517
If the discharge resistor should fail open, then the X -capacitor will not be 518
discharged. Therefore, the X-capacitor value is not to exceed the ES2 limits 519
specified for a charged capacitor. Again, the two components comprise a 520
double safeguard and the values of each component are limited to values 521
for ES1 under normal operating conditions and the values for ES2 under 522
single fault conditions. 523
4.1.1 Application of requirements and acceptance of materials, components and 524
subassemblies 525
Purpose: To accept components as safeguards. 526
Rationale: This document includes requirements for safeguard components. A 527
safeguard component is a component specifically designed and 528
manufactured for both functional and safeguard parameters. Examples of 529
safeguard components are capacitors complying with IEC 60384-14 and 530
other components that comply with their related IEC component document. 531
Acceptance of components and component requirements from 532
IEC 60065 and 60950-1 533
Purpose: To accept both components and sub-assemblies investigated to the legacy 534
documents, IEC 60065 and IEC 60950-1, and components complying with 535
individual component requirements within these documents during the 536
transition period. 537
Rationale: To facilitate a smooth transition from the legacy documents IEC 60065 and 538
IEC 60950-1 to IEC 62368-1, including by the component supply chain, this 539
document allows for acceptance of both components and sub -assemblies 540
investigated to the legacy documents. Individual component requirements 541
within these documents may be used for compliance with IEC 62368-1 542
without further investigation , other than to give consideration to the 543
appropriate use of the component or sub-assembly in the end-product. 544
This means, for example, if a switch mode power supply is certified to 545
IEC 60065 or IEC 60950-1, this component can be used in equipment 546
evaluated to IEC 62368-1 without further investigation , other than to give 547
consideration to the appropriate use of the component, such as use within 548
its electrical ratings. 549
– 18 – IEC TR 62368-2:2019 © IEC 2019
This also means, for example, since IEC 60950-1 allows for wiring and 550
cables insulated with PVC, TFE, PTFE, FEP, polychloroprene or polyimide 551
to comply with material requirements for parts within a fire enclosure 552
without need for the application of a flammability test, the same wire can be 553
used to comply with the requirements in 6.5.2 for insulation on wiring used 554
in PS2 or PS3 circuits and without the need for application of a flammability 555
test per IEC 60332 series or IEC TS 60695-11-21 as normally is required 556
by 6.5.1. 557
4.1.5 Constructions and components not specifically covered 558
For constructions not covered, consideration should be given for the 559
hierarchy of safeguards in accordance with ISO/IEC Guide 51. 560
4.1.6 Orientation during transport and use 561
See also 4.1.4 562
In general, equipment is assumed to be installed and used in accordance 563
with the manufacturer’s instructions. However, in some cases where 564
equipment may be installed by an ordinary person, it is recognized that it 565
is common practice to mount equipment as desired if screw holes are 566
provided, especially if they allow mounting to readily available brackets. 567
Hence, the exception that is added to 4.1.6. 568
Examples of the above: a piece of equipment, such as a television set or a 569
video projector, that has embedded screw mounting holes that allow it to be 570
attached to a wall or other surface through the use of commercially 571
available vertically or tilt -mountable brackets, shall also take into account 572
that the mounting surface itself may not be vertical. 573
It is also recognized that transportable equipment , by its nature, may be 574
transported in any and all orientations. 575
4.1.8 Liquids and liquid filled components (LFC) 576
The one-litre (1 l) restriction was placed in 4.1.8 since the ori gin of some of 577
the requirements in Clause G.15 came from requirements in documents 578
often applied to smaller systems. Nevertheless, such a limitation does not 579
always negate the allowed application of 4.1.8 and Clause G.15 to systems 580
with larger volumes of l iquid, but it could impact direct (automatic) 581
applicability to the larger systems. 582
4.2 Energy source classifications 583
Classification of energy sources may be done whether the source is 584
accessible or not. The requirements for parts may differ on whether the 585
part is accessible or not. 586
4.2.1 Class 1 energy source 587
A class 1 energy source is a source that is expected not to create any pain 588
or injury. Therefore, a class 1 energy source may be accessible by any 589
person. 590
Under some specific conditions of abnormal operation or single fault 591
conditions, a class 1 energy source may reach class 2 limits. However, 592
this source still remains a class 1 energy source. In this case, an 593
instructional safeguard may be required. 594
Under normal operating conditions and abnormal operating conditions, 595
the energy in a class 1 source, in contact with a body part, may be 596
detectable, but is not painful nor is it likely to cause an injury. For fire, the 597
energy in a class 1 source is not likely to cause ignition. 598
Under single fault conditions, a class 1 energy source, under contact with 599
a body part, may be painful, but is not likely to cause injury. 600
IEC TR 62368-2:2019 © IEC 2019 – 19 –
4.2.2 Class 2 energy source 601
A class 2 energy source is a source that may create pain, but which is 602
unlikely to create any serious injury. There fore, a class 2 energy source 603
may not be accessible by an ordinary person. However, a class 2 energy 604
source may be accessible by: 605
– an instructed person; and 606
– a skilled person. 607
The energy in a class 2 source, under contact with a body part, may be 608
painful, but is not likely to cause an injury. For fire, the energy in a class 2 609
source can cause ignition under some conditions. 610
4.2.3 Class 3 energy source 611
A class 3 energy source is a source that is likely to create an injury . 612
Therefore a class 3 energy source may not be accessible to an ordinary 613
person or an instructed person. A class 3 energy source may, in general, 614
be accessible to a skilled person. 615
Any source may be declared a class 3 energy source without measurement, 616
in which case all the safeguards applicable to class 3 are required. 617
The energy in a class 3 source, under contact with a body part, is capable 618
of causing injury. For fire, the energy in a class 3 source may cause ignition 619
and the spread of flame where fuel is available. 620
4.3.2 Safeguards for protection of an ordinary person 621
The required safeguards for the protection of an ordinary person are given in Figure 4. 622
623
Figure 4 – Safeguards for protecting an ordinary person 624
4.3.3 Safeguards for protection of an instructed person 625
The required safeguards for the protection of an instructed person are given in Figure 5. 626
– 20 – IEC TR 62368-2:2019 © IEC 2019
627
Figure 5 – Safeguards for protecting an instructed person 628
4.3.4 Safeguards for protection of a skilled person 629
The required safeguards for the protection of a skilled person are given in Figure 6. 630
631
Figure 6 – Safeguards for protecting a skilled perso n 632
Table 1 in this document gives a general overview of the required number 633
of safeguards depending on the energy source and the person to whom 634
the energy source is accessible. The different clauses have requirements 635
that sometimes deviate from the general principle as given above. These 636
cases are clearly defined in the requirements sections of the document. 637
Table 1 – General summary of required safeguards 638
Person
Number of safeguards required to be interposed between an energy source and a person
Class 1 Class 2 Class3
Ordinary person 0 1 2
Instructed person 0 0 2
Skilled person 0 0 0 or 1
639
For a skilled person, there is normally no safeguard required for a class 3 640
energy source. However, if there are multiple class 3 energy sources 641
accessible or if the energy source is not obvious, a safeguard may be 642
required. 643
IEC TR 62368-2:2019 © IEC 2019 – 21 –
4.4.2 Composition of a safeguard 644
Purpose: To specify design and construction criteria for a single safeguard (basic, 645
supplementary, or reinforced) comprised of more than one element, for 646
example, a component or a device. 647
Rationale: Safeguards need not be a single, homogeneous component. Indeed, some 648
parts of this document require a single safeguard be comprised of two or 649
more elements. For example, for thin insulation, two or more layers are 650
required to qualify as supplementary insulation . Another example is 651
protective bonding and protective earthing, both of which are comprised 652
of wires, terminals, screws, etc. 653
If a safeguard is comprised of two or more elements, then the function of 654
the safeguard should not be compromised by a failure of any one element. 655
For example, if a screw attaching a protective earthing wire should 656
loosen, then the current-carrying capacity of the protective earthing circuit 657
may be compromised, making its reliability uncertain . 658
4.4.3 Safeguard robustness 659
Rationale: Safeguards should be sufficiently robust to withstand the rigors of 660
expected use throughout the equipment lifetime. Robustness requirements 661
are specified in the various clauses. 662
4.4.3.4 Impact test 663
Rationale: Stationary equipment can, in some cases, be developed for a specific 664
installation in which it is not possible for certain surfaces to be subjected to 665
an impact when installed as intended. In those cases, the impact test is not 666
necessary when the installation makes clear that the side cannot be 667
impacted. 668
4.4.3.6 Glass impact tests 669
Source: IEC 60065 670
Purpose: Verify that any glass that breaks does not cause skin -lacerating injury, or 671
expose class 3 hazards behind the glass. 672
Rationale: When it comes to glass, two hazards can be present in case the glass 673
breaks: 674
− access to sharp edges from the broken glass itself 675
− exposure of class 3 energy hazards in case the glass is used as (part of) 676
the enclosure. 677
Should the glass break during the impact test, T.9 is applied to ensure the 678
expelled fragments will be at MS2 level or less. 679
Platen glass has a long history of being exempted, because it is quite 680
obvious for people that, if broken, the broken glass is hazardous and 681
contact should be avoided. There is no known history of serious injuries 682
with this application. Platen glass is the glass that is typically used in 683
scanners, copiers, etc. Accidents are rare, probably also because they are 684
protected by an additional cover most of the time, which limits the 685
probability that an impact will occur on the glass. 686
CRTs are exempted because they have separate requirements. 687
The test value for floor standing equipment is higher because it is more 688
likely to be impacted by persons or carts and dollies at a higher force while 689
in normal use. 690
The exemption for glass below certain sizes is taken over from IEC 60065. 691
There is no good rationale to keep the exemption, other than that there are 692
no serious accidents known from the field. The HBSDT d ecided that they 693
want to keep the exemption in. 694
– 22 – IEC TR 62368-2:2019 © IEC 2019
The flow chart in Figure 7 in this document shows the intent for the 695
requirements. 696
697
Figure 7 – Flow chart showing the intent of the glass requirements 698
4.4.3.10 Compliance criteria 699
The value of 30 g for the weight limit is chosen based on the maximum 700
dimension of a side of 50 mm. A typical piece of glass with a size of 50 mm 701
× 50 mm × 4 mm (roughly 2,80 g/cm3) would have a weight of around 30 g. 702
4.6 Fixing of conductors 703
Source: IEC 60950-1 704
Purpose: To reduce the likelihood that conductors could be displaced such that they 705
reduce the creepage distances and clearances. 706
Rationale: These requirements have been successfully used for products in the scope 707
of this document for many years. 708
4.7 Equipment for direct insertion into mains socket -outlets 709
Source: IEC 60065:2014, 15.5 710
IEC 60950-1:2013, 4.3.6 711
IEC 60335-1:2010, 22.3 712
IEC TR 62368-2:2019 © IEC 2019 – 23 –
IEC 60884-1:2013, 14.23.2 713
Purpose: Determine that equipment incorporating integr al pins for insertion into 714
mains socket-outlets does not impose undue torque on the socket -outlet 715
due to the mass and configuration of the equipment. This type of equipment 716
often is known as Direct Plug-in Equipment or Direct Plug-in Transformers. 717
Rationale: Socket outlets are required to comply with the safety requirements in 718
IEC 60884-1:2013, Plugs and socket-outlets for household and similar 719
purposes – Part 1: General requirements , including subclause 14.23.2. The 720
requirements result in socket designs wi th certain design limitations. 721
Equipment incorporating integral pins for insertion into mains socket-722
outlets is not allowed to exceed these design limitations. 723
4.9 Likelihood of fire or shock due to entry of conductive objects 724
Purpose: The purpose of this subclause is to establish opening requirements that 725
would minimize the risk of foreign conductive objects falling into the 726
equipment that could bridge parts within class 2 or class 3 circuits, or 727
between PS circuits that could result in ignition or electric shock. 728
It is considered unlikely that a person would accidentally drop something 729
that could consequently fall into the equipment at a height greater than 730
1,8 m. 731
_____________ 732
5 Electrically-caused injury 733
Purpose: Clause 5 classifies electrical energy sources and provides criteria for 734
determining the energy source class of each conductive part. The criteria 735
for energy source class include the source current -voltage characteristics, 736
duration, and capacitance. Each conductive part, whether current -carrying 737
or not, or whether earthed or not, shall be classed ES1, ES2, or ES3 with 738
respect to earth and with respect to any other simultaneously accessible 739
conductive part. 740
240 VA limit 741
IEC 62368-1 does not have requirements for a 240 VA energy hazard that 742
was previously located in 2.1.1.5 of IEC 60950-1:2013. 743
The origin/justification of the 240 VA energy hazard requirement in the 744
legacy documents was never precisely determined, and it appears the VA 745
limits may have come from a manufacturer’s specifications original ly 746
applied to exposed bus bars in mainframe computers back in the 1960 ’s 747
and concerns at the time service personnel inadvertently bridging them wit h 748
a metal part. 749
However, when IEC TC 108 started the IEC 62368-1 project the intent was 750
to take a fresh look at product safety using HBSE and only carry over a 751
legacy requirement if the safety science and HBSE justified it. After 752
considerable study by IEC TC 108, there was no support for carrying over 753
the 240 VA requirement since: 754
− the requirements were not based on any proven science or sound 755
technical basis; 756
− the 240 VA value was relatively arb itrary; and 757
− in practice the requirement was difficult to apply consistently (for 758
example, on a populated printed board or inside a switch mode power 759
supply). 760
In the meantime, there are energy limits for capacitors in Clause 5, which 761
remains a more realistic concern and which were the second set of the 762
energy hazard requirements in IEC 60950-1, the first being steady state 763
240 VA. 764
– 24 – IEC TR 62368-2:2019 © IEC 2019
In addition, there are other requirements in IEC 62368-1 that will limit 765
exposure to high levels of power (VA), including a VA limit for LPS outputs 766
when those are required by Annex Q (for outputs connected to buil ding 767
wiring as required by 6.5.2). 768
Electric burn (eBurn) 769
Analysis of the body current generated by increasing frequency sinusoidal 770
waveforms shows that the current continues to increase with frequency. 771
The same analysis shows that the touch current, which is discounted with 772
frequency, stabilizes. 773
The following paper describes the analysis fully: ‘Touch Current 774
Comparison, Looking at IEC 60990 Measurement Circuit Performance – 775
Part 1: Electric Burn'; Peter E Perkins; IEEE PSES Product Safety 776
Engineering Newsletter, Vol 4, No 2, Nov 2008. 777
The crossover frequency is different for the startle -reaction circuit than for 778
the let go-immobilization circuit because of the separate Frequency Factor 779
body response curves related to current levels; analysis identifies the 780
crossover frequency where the eBurn current surpasses the touch current. 781
Under these conditions, a person touching the circuit will become 782
immobilized and will not be able to let go of the circuit. This crossover 783
frequency is determined in the analysis. The person contacting the circuit 784
should always be able to let go. 785
The general conditions that apply to eBurn circuits are: 786
− the eBurn limit only applies to HF sinusoidal signals; 787
− the area of contact should be limited to a small, fingertip contact 788
(~ 1cm2); 789
− the contact time should be less than 1 s; at this short contact time, it is 790
not reasonable to define different levels for various persons; 791
This requirement applies to accessible circuits that can be contacted at 792
both poles, including all grounded circuits isolated from the mains and any 793
isolated circuits where both contacts are easily available to touch. 794
A simplified application of these requirements in the documents limits the 795
accessibility of HF sinusoidal currents above a specified frequency. The 796
22 kHz and 36 kHz frequency limits are where the eBurn current crosses 797
the 5mA limit for the ES1 and ES2 measurement circuits. This will ensure 798
that the person contacting the circuit will be able to remove themselves 799
from the circuit under these conditions. 800
1 MHz limit 801
The effects of electric current on the human body are described in the 802
IEC 60479 series and the requirements in IEC 62368-1 are drawn from 803
there. The effects versus frequency are well laid out and properly 804
accounted for in these requirements . The body effects move from 805
conducted effects to surface radiofrequency burns at higher frequencies 806
approaching 100 kHz. By long-term agreement, IEC safety documents are 807
responsible for outlining the effects of current to 1 MHz, which are properly 808
measured by the techniques given herein . Above the 1 MHz level, it 809
becomes an EMC issue. Unless the current is provided as a principal action 810
of the equipment operation, electric shock evaluation should not be needed 811
above the 1 MHz level. Where it is fundamental to the equipment 's 812
operation, the high-frequency current levels shall be specially measured 813
using proper high-frequency techniques, including classifying the circuits 814
and, if necessary, appropriately protected to avoid any bodily injury. 815
IEC TR 62368-2:2019 © IEC 2019 – 25 –
5.2.1 Electrical energy source classification s 816
Source: IEC TS 60479-1:2005 and IEC 61201 817
Purpose: To define the line between hazardous and non-hazardous electrical energy 818
sources for normal operating conditions and abnormal operating 819
conditions. 820
Rationale: The effect on persons from an electric source depend s on the current 821
through the human body. The effects are described in IEC TS 60479-1. 822
IEC TS 60479-1 (see Figures 20 and 22, Tables 11 and 13); zone AC-1 and 823
zone DC-1; usually no reaction (Figure 8 and Figure 9, Table 2 and Table 3 824
in this document) is taken as values for ES1. 825
IEC TS 60479-1 (see Figures 20 and 22; Tables 11 and 13); zone AC-2 and 826
zone DC-2; usually no harmful physiological effects (see Figure 8 and 827
Figure 9, Table 2 in this document) is taken as values for ES2. 828
IEC TS 60479-1; zone AC-3 and zone DC-3; harmful physiological effects 829
may occur (see Figure 8 and Figure 9, Table 2 and Table 3 in this 830
document) is the ES3 zone. 831
832
833
Figure 8 – Conventional time/current zones of effects 834
of AC currents (15 Hz to 100 Hz) on persons for a cur rent path corresponding 835
to left hand to feet (see IEC TS 60479-1:2005, Figure 20) 836
– 26 – IEC TR 62368-2:2019 © IEC 2019
Table 2 – Time/current zones for AC 15 Hz to 100 Hz 837
for hand to feet pathway (see IEC TS 60479-1:2005, Table 11) 838
Zones Boundaries Physiological effects
AC-1 up to 0,5 mA curve a Perception possible but usually no startle reaction
AC-2 0,5 mA up to curve b Perception and involuntary muscular contractions likely but usually no harmful electrical physiological effects
AC-3 Curve b and above Strong involuntary muscular contractions. Difficulty in breathing.
Reversible disturbances of heart function. Immobilisation may occur.
Effects increasing with current magnitude. Usually no organic damage to be expected.
AC-4a Above curve c1 Pathophysiological effects may occur such as cardiac arrest,
breathing arrest, and burns or other cellular damage. Probability of ventricular fibrillation increasing with current magnitude and time.
c1 – c
2 AC-4.1 Probability of ventricular fibrillation increasing up to about
5 %.
c2 – c
3 AC-4.2 Probability of ventricular fibrillation up to about 50 %.
Beyond curve c3 AC-4.3 Probability of ventricular fibrillation above 50 %.
a For durations of current flow below 200 ms, ventricular fibrillation is only initiated within t he vulnerable period if the relevant thresholds are surpassed. As regards ventricular fibrillation , this figure relates to the effects of current that flows in the path left hand to feet. For other current paths , the heart current factor has to be considered.
839
840
Figure 9 – Conventional time/current zones of effects of DC currents on persons for 841
a longitudinal upward current path (see IEC TS 60479-1:2005, Figure 22) 842
IEC TR 62368-2:2019 © IEC 2019 – 27 –
Table 3 – Time/current zones for DC for hand to feet pathway 843
(see IEC TS 60479-1:2005, Table 13) 844
Zones Boundaries Physiological effects
DC-1 Up to 2 mA curve a Slight pricking sensation possible when making, breaking or rapidly altering current flow.
DC-2 2 mA up to curve b Involuntary muscular contractions likely , especially when making, breaking or rapidly altering current flow , but usually no harmful electrical physiological effects
DC-3 curve b and above Strong involuntary muscular reactions and reversible disturbances of formation and conduction of impulses in the heart may occur, increasing with current magnitude and time. Usually no organic damage to be expected.
DC-4a Above curve c1 Pathophysiological effects may occur such as cardiac arrest,
breathing arrest, and burns or other cellula r damage. Probability of ventricular fibrillation increasing with current magnitude and time.
c1 – c
2 DC-4.1 Probability of ventricular fibrillation increasing up to about
5 %.
c2 – c
3 DC-4.2 Probability of ventricular fibrillation up to about 50 %.
Beyond curve c3 DC-4.3 Probability of ventricular fibrillation above 50 %.
a For durations of current flow below 200 ms, ventricular fibrillation is only initiated within the vulnerable period if the relevant thresholds are surpassed. As regards ventricu lar fibrillation, this figure relates to the effects of current which flows in the path left hand to feet and for upward current. For other current paths , the heart current factor has to be considered.
845
The seriousness of an injury increases continuously with the energy 846
transferred to the body. To demonstrate this principle Figure 8 and Figure 9 847
in this document (see IEC TS 60479-1, Figures 20 and 22) are transferred 848
into a graph: effects vs energy (see Figure 10 in this document). 849
850
Figure 10 – Illustration that limits depend on both voltage and current 851
Within the document, only the limits for Zone 1 (green) and Zone 2 (yellow) 852
will be specified. 853
Curve “a” (limit of Zone 1) will be the limit for parts accessible by an 854
ordinary person during normal use. 855
Curve “b” (limit of Zone 2) will be the limit for parts accessible by an 856
ordinary person during (or after) a single fault. 857
– 28 – IEC TR 62368-2:2019 © IEC 2019
IEC TC 108 regarded it not to be acceptable to go to the limits of either 858
Zone 3 or 4. 859
In the document three (3) zones are described as electrical energy sources. 860
This classification is as follows: 861
– electrical energy source 1 (ES1): levels are of such a value that they do 862
not exceed curve “a” (threshold of perception) of Figure 8 and Figure 9 863
in this document (see IEC TS 60479-1:2005, Figures 20 and 22). 864
– electrical energy source 2 (ES2): levels are of such a value that they 865
exceed curve “a”, but do not exceed curve “b” (threshold of let go) of 866
Figure 8 and Figure 9 in this document (see IEC TS 60479-1:2005, 867
Figures 20 and 22). 868
– electrical energy source 3 (ES3): levels are of such a value that they 869
exceed curve “b” of Figure 8 and Figure 9 in this document (see IEC 870
TS 60479-1:2005, Figures 20 and 22). 871
5.2.2.1 General 872
When classifying a circuit or part that is not accessible, that circuit or part 873
shall be regarded as being accessible when measuring prospective touch 874
voltage and touch current. 875
5.2.2.2 Steady-state voltage and current limits 876
Table 4 Electrical energy source limits for steady-state ES1 and ES2 877
Source: IEC TS 60479-1:2005, Dalziel, Effect of Wave Form on Let -Go Currents; 878
AIEE Electrical Engineering Transactions, Dec 1943, Vol 62. 879
Rationale: The current limits of Table 4 line 1 and 2 are derived from curve a and b, 880
Figure 8 and Figure 9 in this document (see IEC TS 60479-1:2005, Figures 881
20 and 22). 882
The basis for setting limits for combined AC and DC touch current is from 883
the work of Dalziel which provides clear data for men, women and children. 884
In the current diagram (Figure 22), the AC current is always the peak value 885
(per Dalziel). In the voltage diagram (Figure 23), the 30 V AC and 50 V AC 886
points on the baseline are recognized as AC RMS values as stated in 887
Table 4. Since IEC TC 108 is working with consumer appliances, there is a 888
need to provide protection for children, who are generally considered the 889
most vulnerable category of people . The formulas of IEC 62368-1:2018, 890
Table 4 address the Dalziel investigations. 891
Under single fault conditions of a relevant basic safeguard or 892
supplementary safeguard, touch current is measured according to 5.1.2 893
of IEC 60990:2016. However, this IEC 60990 subclause references both 894
the IEC 60990 perception/reaction network (Figure 4) and the let -go 895
network (Figure 5), selection of which depends on several factors. Figure 5 896
applies to touch current limits above 2 mA RMS. IEC TC 108 has decided 897
that parts under single fault conditions of relevant basic safeguards or 898
supplementary safeguards should be measured per Figure 5 (let -go 899
immobilization network). Therefore, since 5.1.2 makes reference to both 900
Figure 4 and Figure 5, for clarification Table 4 is mentioned directly in 901
5.2.2.2. 902
Because there is usually no reaction of the human body when touching 903
ES1, access is permitted by any person (IEC TS 60479-1; zone AC-1 and 904
zone DC-1). 905
Because there may be a reaction of th e human body when touching ES2, 906
protection is required for an ordinary person. One safeguard is sufficient 907
because there are usually no harmful physiological effects when t ouching 908
ES2 (IEC TS 60479-1:2005; zone AC-2 and zone DC-2). 909
IEC TR 62368-2:2019 © IEC 2019 – 29 –
Because harmful physiological effects may occur when touching ES3, (IEC 910
TS 60479-1:2005; zone AC-3 and zone DC-3), protection is required for an 911
ordinary person and an instructed person, including after a fault of one 912
safeguard. 913
During the application of the electrical energy source limits for “combined 914
AC and DC” in Table 4, if the AC component of a superimposed AC and DC 915
energy source does not exceed 10 % of the DC energy, then the AC 916
component can be disregarded for purposes of application of Table 4. This 917
consideration is valid based on the definition of DC voltage in 3.3.14.1, 918
which allows peak-to-peak ripple not exceeding 10 % of the average value 919
to integrated into DC voltage considerations. As a result, in such cases 920
where AC does not exceed 10 % of DC, only the DC energy source limits in 921
Table 4 need be applied. 922
When measuring combined AC and DC voltages and currents, both AC and 923
DC measurements shall be made between the same points of reference. 924
Do not combine common-mode measurements with differential-mode 925
measurements. They shall be assessed separately. 926
In using Table 4, ES1 touch current measurement specifies the startle -927
reaction circuit ‘a’ intended for limits less than 2 mA RMS / 2,8 mA peak 928
and ES2 touch current specifies the let -go-immobilization circuit ‘b’ 929
intended for limits > 2 mA RMS / 2,8 mA peak. These circuits are adopted 930
from IEC 60990:2016, Clause 5. 931
Normal operating conditions of equipment for touch current testing are 932
outlined in 5.7.2 and Clause B.2 of IEC 62368-1:2018 and includes 933
operation of all operator controls. Abnormal operating conditions are 934
specified in Clause B.3 of IEC 62368-1:2018. Single fault conditions 935
(within the equipment), specified in Clause B.4 of IEC 62368-1:2018, 936
includes faults of a relevant basic safeguard or a supplementary 937
safeguard. 938
5.2.2.3 Capacitance limits 939
Table 5 Electrical energy source limits for a charged capacitor 940
Source: IEC TS 61201:2007 (Annex A) 941
Rationale: Where the energy source is a capacitor, the energy source class is 942
determined from both the charge voltage and the capacitance. The 943
capacitance limits are derived from IEC TS 61201:2007, see Table 4 in this 944
document. 945
The values for ES2 are derived from Table A .2 of IEC TS 61201:2007. 946
The values for ES1 are calculated by dividing the values from Table A .2 of 947
IEC TS 61201:2007 by two (2). 948
– 30 – IEC TR 62368-2:2019 © IEC 2019
Table 4 – Limit values of accessible capacitance (threshold of pain) 949
U
V
C
F
U
kV
C
nF
70 42,4 1 8,0
78 10,0 2 4,0
80 3,8 5 1,6
90 1,2 10 0,8
100 0,58 20 0,4
150 0,17 40 0,2
200 0,091 60 0,133
250 0,061
300 0,041
400 0,028
500 0,018
700 0,012
950
5.2.2.4 Single pulse limits 951
Table 6 Voltage limits for single pulses 952
Rationale: The values are based on the DC current values of Table 4, assuming 953
25 mA gives a voltage of 120 V DC (body resistance of 4,8 kΩ). The lowest 954
value is taken as 120 V because, under single fault conditions, the 955
voltage of ES1 can be as high as 120 V DC without a time limit. 956
The table allows linear interpolation because the difference is considered to 957
be very small. However, the following formula may be used for a more 958
exact interpolation of the log-log based values in this table. The variable t 959
or V is the desired unknown "in between value" and either may be 960
determined when one is known: 961
22 1
1
2
1
–
–
–1
–
log loglog log
log logAntilog
log log
log log
t tV V
t tV
t t
t t
+
=
+
962
and 963
22 1
1
2
1
–
–
–1
–
log loglog log
log logAntilog
log log
log log
V Vt t
V Vt
V V
V V
+
=
+
964
where: 965
t is the time duration that is required to be determined if Upeak
voltage V is known (or t 966 is known and V needs to be determined) 967
t1 is the time duration adjacent to t corresponding to the U
peak voltage V
1 968
t2 is the time duration adjacent to t corresponding to the U
peak voltage V
2 969
V is the Upeak
voltage value that is known if time duration t is to be determined (or V is 970
required to be determined if time duration t is known) 971
V1 is the value of the voltage U
peak adjacent to V corresponding to time duration t
1 972
V2 is the value of the voltage U
peak adjacent to V corresponding to time duration t
2 973
IEC TR 62368-2:2019 © IEC 2019 – 31 –
Table 7 Current limits for single pulses 974
Source: IEC TS 60479-1:2005 975
Rationale: For ES1, the limit of single pulse should not exceed the ES1 steady-state 976
voltage limits for DC voltages. 977
For ES2, the voltage limits have been calculated by using the DC current 978
values of curve b Figure 9 in this document and the resistance values of 979
Table 10 of IEC TS 60479-1:2005, column for 5 % of the population (see 980
Table 5 in this document). 981
The current limits of single pulses in Table 7 for ES1 levels are from curve 982
a and for ES2 are from curve b of Figure 9 in this document. 983
The table allows linear interpolation because the difference is considered to 984
be very small. However, the following formula may be used for a more 985
exact interpolation of the log-log based values in this table. The variable t 986
or I is the desired unknown "in between value" and either may be 987
determined when one is known: 988
989
22 1
1
2
1
–
–
–1
–
log loglog log
log logAntilog
log log
log log
t tI I
t tI
t t
t t
+
=
+
990
and 991
22 1
1
2
1
–
–
–1
–
log loglog log
log logAntilog
log log
log log
I It t
I It
I I
I I
+
=
+
992
where: 993
t is the time duration that is required to be determined if the electric current I is 994 known (or t is known and I needs to be determined) 995
t1 is the time duration adjacent to t corresponding to the electric current I
1 996
t2 is the time duration adjacent to t corresponding to the electric current I
2 997
I is the value of the Ipeak
current that is known if time duration t is to be determined 998 (or I is required to be determined if time duration t is known) 999
I1 is the value of the I
peak adjacent to I corresponding to time duration t
1 1000
I2 is the value of the I
peak adjacent to I corresponding to time duration t
2 1001
– 32 – IEC TR 62368-2:2019 © IEC 2019
Table 5 – Total body resistances RT for a current path hand to hand, DC, 1002
for large surface areas of contact in dry condition 1003
Touch voltage
V
Values for the total body resistance RT ()
that are not exceeded for
5 % of the
population
50 % of the
population
95 % of the
population
25
50
75
100
125
150
175
200
225
400
500
700
1 000
2 100
1 600
1 275
1 100
975
875
825
800
775
700
625
575
575
3 875
2 900
2 275
1 900
1 675
1 475
1 350
1 275
1 225
950
850
775
775
7 275
5 325
4 100
3 350
2 875
2 475
2 225
2 050
1 900
1 275
1 150
1 050
1 050
Asymptotic value 575 775 1 050
NOTE 1 Some measurements indicate that the total body resistance RT for the current path hand to foot
is somewhat lower than for a current path hand to hand (10 % to 30 %).
NOTE 2 For living persons the values of RT correspond to a duration of current flow of about 0,1 s.
For longer durations RT values may decrease (about 10 % to 20 %) and after complete rupture
of the skin RT approaches the initial body resistance Ro.
NOTE 3 Values of RT are rounded to 25 .
1004
1005
5.2.2.6 Ringing signals 1006
Source: EN 41003 1007
Purpose: To establish limits for analogue telephone network ringing signals . 1008
Rationale: For details see rationale for Annex H. Where the energy source is an 1009
analogue telephone network ringing signal as defined in Annex H, the 1010
energy source class is taken as ES2 (as in IEC 60950-1:2005, Annex M). 1011
5.2.2.7 Audio signals 1012
Source: IEC 60065:2014 1013
Purpose: To establish limits for touch voltages for audio signals . 1014
Rationale: The proposed limits for touch voltages at terminals involving audio signals 1015
that may be contacted by persons have been extracted without deviation 1016
from IEC 60065. Reference: IEC 60065:2014, 9.1.1.2 a). Under single 1017
fault conditions, 10.2 of IEC 60065:2014 does not permit an increase in 1018
acceptable touch voltage limits. 1019
IEC TR 62368-2:2019 © IEC 2019 – 33 –
The proposed limits are quantitatively larger than the accepted limits of 1020
Tables 5 and 6, but are not considered danger ous for the following 1021
reasons: 1022
– the output is measured with the load disconnected (worst case load) ; 1023
– defining the contact area of connectors and wiring is very difficult due to 1024
complex shapes. The area of contact is considered small due to the 1025
construction of the connectors; 1026
– normally, it is recommended to the user, in the instruction manual 1027
provided with the equipment, that all connections be made with the 1028
equipment in the “off” condition; 1029
– in addition to being on, the equipment would have to be pla ying some 1030
program at a high output with the load disconnected to achieve the 1031
proposed limits (although possible, highly unlikely). Historically, no 1032
known cases of injury are known for amplifiers with non -clipped output 1033
less than 71 V RMS; 1034
– the National Electrical Code (USA) permits accessible terminals with 1035
maximum output voltage of 120 V RMS. 1036
5.3.2 Accessibility to electrical energy sources and safeguards 1037
1038
What are the requirements between the non-accessible sources? 1039
Answer: None. As the enclosure is double insulated, the sources are not 1040
accessible. 1041
1042
Now there is an accessible connection. What are the requirements 1043
between the sources in this case? 1044
– 34 – IEC TR 62368-2:2019 © IEC 2019
Answer: 1045
– Basic insulation between ES1 and ES2 1046
– Double insulation or reinforced insulation between ES1 and ES3 1047
– The insulation between ES2 and ES3 depends on the insulation 1048
between the ES1 and ES2 1049
1050
Now there are two accessible connections from independent sources. 1051
What are the requirements between the sources in this case? 1052
Answer: 1053
– According to Clause B.4, the insulation or any components between the 1054
sources need to be shorted 1055
– If one of the two ES1 sources would reach ES2 levels basic 1056
safeguard 1057
– If both ES1 sources stay within ES1 limits no safeguard (functional 1058
insulation) 1059
For outdoor equipment, lower voltage limits apply because the body 1060
impedance is reduced to half the value when subjected to wet conditions as 1061
described in IEC TS 60479-1 and IEC TS 61201. 1062
Where Class III equipment is acceptable in an indoor application , this outdoor 1063
application does not introduce additional safeguard requirements. 1064
5.3.2.2 Contact requirements 1065
Source: IEC 61140:2001, 8.1.1 1066
Purpose: Determination of accessible parts for adults and children. Tests are in 1067
IEC 62368-1:2018, Annex V. 1068
Rationale: According to Paschen’s Law, air breakdown does not occur below 1069
323 V peak or DC (at sea level). IEC 62368-1:2018 uses 420 V peak (300 V 1070
RMS) to add an additional safety margin. 1071
5.3.2.3 Compliance criteria 1072
The reason for accepting different requirements for components is because 1073
you cannot expect your supplier to make different components for each end 1074
application. 1075
5.3.2.4 Terminals for connecting stripped wire 1076
Source: IEC 60065 1077
Purpose: To prevent contact of ES2 or ES3 parts . 1078
IEC TR 62368-2:2019 © IEC 2019 – 35 –
Rationale: Accepted constructions used in the audio/video industry for many years. 1079
5.4 Insulation materials and requirements 1080
Rationale: The requirements, test methods and compliance criteria are taken from the 1081
actual outputs from IEC TC 108 MT2 (formerly WG6) as well as from IEC 1082
TC 108 MT1. 1083
– The choice and application of components shall take into account the 1084
needs for electrical, thermal and mechanical strength, frequency of the 1085
working voltage and working environment (temperature, pressure, 1086
humidity and pollution). 1087
– Components shall have the electric strength, thermal strength, 1088
mechanical strength, dimensions, and other properties as specified in 1089
the document. 1090
– Depending on the grade of safeguard (basic safeguard, 1091
supplementary safeguard, reinforced safeguard) the requirements 1092
differ. 1093
– Components complying with their component documents (for example, 1094
IEC 60384-14 for capacitances) have to be verified for their application. 1095
– The components listed in this subclause of the new document have a 1096
separation function. 1097
5.4.1.1 Insulation 1098
Source: IEC 60664-1 1099
Purpose: Provide a reliable safeguard 1100
Rationale: Solid basic insulation, supplementary insulation, and reinforced 1101
insulation shall be capable of durably withstanding electrical, mechanical, 1102
thermal, and environmental stress that may occur during the anticip ated 1103
lifetime of the equipment. 1104
Clearances and creepage distances may be divided by intervening 1105
unconnected (floating) conductive parts, such as unused contacts of a 1106
connector, provided that the sum of the individual distances meets the 1107
specified minimum requirements (see Figure O.4). 1108
5.4.1.4 Maximum operating temperatures for materials , components and systems 1109
Source: IEC 60085, IEC 60364-4-43, ISO 306, IEC 60695-10-2 1110
Rationale: Temperature limits given in Table 9: 1111
– limits for insulation materials including electrical insulation systems, 1112
including winding insulation (C lasses A, E, B, F, H, N, R and 250) are 1113
taken from IEC 60085; 1114
– limits for insulation of internal and external wiring, including power 1115
supply cords with temperature marking are those indi cated by the 1116
marking or the rating assigned by the (component) manufacturer ; 1117
– limits for insulation of internal and external wiring, including power 1118
supply cords without temperature marking of 70 °C are referenced in 1119
IEC 60364-4-43 for an ambient temperature of 25 °C; 1120
– limits for thermoplastic insulation are based on: 1121
• data from Vicat test B50 of ISO 306; 1122
• ball pressure test according to IEC 60695-10-2; 1123
• when it is clear from the examination of the physical characteristics of 1124
the material that it will meet the requirements of the ball pressure 1125
test; 1126
– 36 – IEC TR 62368-2:2019 © IEC 2019
• experience with 125 °C value for parts in a circuit supplied from the 1127
mains. 1128
5.4.1.4.3 Compliance criteria 1129
Table 9 Temperature limits for materials, components and systems 1130
Rationale Regarding condition “a”, it has been assumed by the technical committee 1131
for many years that the thermal gradient between outer surface and inner 1132
windings will be limited to 10 °C differential as an average. As a result, the 1133
temperature limits for outer surface insulation measured via thermocouple 1134
is 10 °C lower than similar measurement with a thermocouple embedded in 1135
the winding(s), with both limits at least 5 °C less than the hot-spot 1136
temperature allowed per IEC 60085 as an additional safety factor. 1137
However, some modern transformer constructions with larger power 1138
densities may have larger thermal gradients, as may some outer surface 1139
transformer insulation thermal measurements in the equipment/system be 1140
influenced by forced cooling or similar effects. Therefore, if thermal 1141
imaging, computer modeling, or actual measurement shows a thermal 1142
gradient greater than 10 °C average between transformer surface 1143
temperature and transformer winding(s), the rise of resistance temperature 1144
measurement method and limits for an embedded thermocouple shoul d be 1145
used (for example, 100 °C maximum temperature for Class 105 (A)) for 1146
determining compliance of a transformer with Table 9 since the original 1147
assumptions do not hold true. 1148
As an example, a material rated for 124 °C using the rise of resistance 1149
method is considered suitable for classes whose temperature is lower 1150
(class with letter codes E and A) and not for classes whose temperature is 1151
higher (class with letter codes B, F, H, N, R and 250). 1152
5.4.1.5 Pollution degrees 1153
Source: IEC 60664-1 1154
Rationale: No values for PD 4 (pollution generates persistent conductivity) are 1155
included, as it is unlikely that such conditions are present when using 1156
products in the scope of the document. 1157
5.4.1.5.2 Test for pollution degree 1 environment and for an insulating compoun d 1158
The compliance check made by visual inspection applies both to single 1159
layer and multi-layer boards without the need for sectioning to check for 1160
voids, gaps, etc. 1161
5.4.1.6 Insulation in transformers with varying dimensions 1162
Source: IEC 60950-1 1163
Purpose: To consider actual working voltage along the winding of a transformer . 1164
Rationale: Description of a method to determine adequacy of solid insulation along 1165
the length of a transformer winding. 1166
5.4.1.7 Insulation in circuits generating starting pulses 1167
Source: IEC 60950-1, IEC 60664-1 1168
Purpose: To avoid insulation breakdown due to starting pulses. 1169
Rationale: This method has been successfully used for products in the scope of this 1170
document for many years. 1171
5.4.1.8 Determination of working voltage 1172
Source: IEC 60664-1:2007, 3.5; IEC 60950-1 1173
IEC TR 62368-2:2019 © IEC 2019 – 37 –
Rationale: The working voltage does not include short duration signals, such as 1174
transients. Recurring peak voltages are not included. Transient 1175
overvoltages are covered in the required withstand voltage. Ringing 1176
signals do not carry external transients. 1177
5.4.1.8.1 General 1178
Rationale: Functional insulation is not addressed in Clause 5, as it does not provide 1179
protection against electric shock. Requirements for functional insulation 1180
are covered in Clause 6, which addresses protection against electrically 1181
caused fire. 1182
Source: IEC 60664-1:2007, 3.8 1183
Rationale: In IEC 62368-1, “Circuit supplied from the mains” is used for a “primary 1184
circuit”. “Circuit isolated from the mains” is used for a “secondary circuit”. 1185
“External circuit” is defined as external to the equipment. ES1 can be 1186
external to the equipment. 1187
For an external circuit operating at ES2 level and not exiting the building, 1188
the transient is 0 V. Therefore, in this case, ringing peak voltage needs to 1189
be taken into account. 1190
5.4.1.8.2 RMS working voltage 1191
Source: IEC 60664-1:2007, 3.5 1192
Rationale: RMS working voltage is used when determining minimum creepage 1193
distance. Unless otherwise specified, working voltage is the RMS value. 1194
5.4.1.10 Thermoplastic parts on which conductive meta llic parts are directly mounted 1195
Source: ISO 306 and IEC 60695-2 series 1196
Rationale: The temperature of the thermoplastic parts under normal operating 1197
conditions shall be 15 K less than the softening temperature of a non -1198
metallic part. Supporting parts in a circuit supplied from the mains shall not 1199
be less than 125 °C. 1200
5.4.2 Clearances 1201
5.4.2.1 General requirements 1202
Source: IEC 60664-1:2007 1203
Rationale: The dimension for a clearance is determined from the required impulse 1204
withstand voltage for that clearance. This concept is taken from 1205
IEC 60664-1:2007, 5.1. In addition, clearances are affected by the largest 1206
of the determined transients. The likelihood of simultaneous occurrence of 1207
transients is very low and is not taken into account . 1208
Overvoltages and transients that may enter the equipment, and peak 1209
voltages that may be generated within the equipment, do not break down 1210
the clearance (see IEC 60664-1:2007, 5.1.5 and 5.1.6). 1211
Minimum clearances of safety components shall comply with the 1212
requirements of their appl icable component safety document. 1213
Clearances between the outer insulating surface of a connector and 1214
conductive parts at ES3 voltage level shall comply with the requirements of 1215
basic insulation only, if the connectors are fixed to the equipment, located 1216
internal to the outer electrical enclosure of the equipment, and are 1217
accessible only after removal of a sub-assembly that is required to be in 1218
place during normal operation. 1219
It is assumed that the occurrence of both factors, the sub-assembly being 1220
removed and the occurrence of a transient overvoltage , have a reduced 1221
likelihood and hazard potential. 1222
– 38 – IEC TR 62368-2:2019 © IEC 2019
Source: IEC 60664-2 series, Application guide 1223
Rationale: The method is derived from the IEC 60664-2 series, Application guide. 1224
Example:
Assuming: – an SMPS power supply, – connection to the AC mains, – a peak of the working voltage (PWV) of 800 V, – frequencies above and below 30 kHz, – reinforced clearances required, – temporary overvoltages: 2 000 V Procedure 1: Table 10 requires 2,54 mm Table 11 requires 0,44 mm Result is 2,54 mm
NOTE All PWV below 1 200 V have clearance requirements less than 3 mm for both Table 10 and Table 11
Procedure 2: Transients (OVC 2): 2 500 V RWV = 2 500 V Table 14 requires 3,0 mm The required ES test voltage according to Table 15 is 4,67 KV Result is 3,0 mm or ES test at 4,67 KV
Final result: – 3,0 mm or – ES test at 4,67 KV and 2,54 mm ATTENTION:
For a product with connection to coax cable, different values are to be used since a different transient and required withstand voltage is required.
IEC TR 62368-2:2019 © IEC 2019 – 39 –
1225
5.4.2.2 Procedure 1 for determining clearance 1226
Rationale: Related to the first dash of 5.4.2.2, it is noted that an example of a cause of 1227
determination of the peak value of steady state voltages that are below the 1228
peak voltage of the mains includes, for example, a determination in 1229
accordance with the 2nd and 3rd dash of 5.4.2.3.3 where filtering is in 1230
place to lower expected peak voltages. 1231
Similarly, related to the second dash of 5.4.2.2, an example of this case 1232
where the recurring peak voltage is limited to 1,1 times the mains voltage 1233
may be use of certain forms of surge protection devices that reduce 1234
overvoltage category. 1235
Peak of the working voltage versus recurring peak voltage. 1236
There has been some discussion between the two terms. The peak of the 1237
working voltage is the peak value of the waveform that occurs each cycle, 1238
and therefore is considered to be a part of the working voltage. 1239
A recurring peak voltage is a peak that does not occur at each cycle of the 1240
waveform, but that reoccurs at a certain interval, usually at a lower 1241
frequency than the waveform frequency. 1242
Figure 11 in this document gives an example of a waveform where the 1243
recurring peak voltage occurs every two cycles of the main waveform . 1244
1245
Figure 11 – Illustration of working voltage 1246
Table 10 Minimum clearances for voltages with frequencies up to 30 kHz 1247
Rationale: IEC TC 108 noted that, if the rules of IEC 60664-1 are followed, for 1248
reinforced clearance, some values were more than double the 1249
requirements for basic insulation. IEC TC 108 felt that this should not be 1250
the case and decided to limit the requirement for reinforced insulation to 1251
twice the value of basic insulation, thereby deviating from IEC 60664-1. 1252
In addition, normal rounding rules were applied to the values in the table. 1253
5.4.2.3.2.2 Determining AC mains transient voltages 1254
Source: IEC 60664-1:2007, 4.3.3.3 1255
Rationale: Table 12 is derived from Table F.1 of IEC 60664-1:2007. 1256
The term used in IEC 60664-1 is ‘rated impulse voltage’. Products covered 1257
by IEC 62368-1 are also exposed to transients from external circuits, and 1258
therefore another term is needed, to show the different source. 1259
– 40 – IEC TR 62368-2:2019 © IEC 2019
Outdoor equipment that is part of the building installation, or that may be 1260
subject to transient overvoltages exceeding those for Overvoltage 1261
Category II, shall be designed for Overvoltage Category III or IV, unless 1262
additional protection is to be provided internally or externally to the 1263
equipment. In this case, the installation instructions shall state the need for 1264
such additional protection. 1265
5.4.2.3.2.3 Determining DC mains transient voltages 1266
Rationale: Transient overvoltages are attenuated by the capacitive filtering. 1267
5.4.2.3.2.4 Determining external circuit transient voltages 1268
Source: ITU-T K.21 1269
Rationale: Transients have an influence on circuits and insulation, therefore transients 1270
on external circuits need to be taken into account. Transients are needed 1271
only for the dimensioning safeguards. Transients should not be used for 1272
the classification of energy sources (ES1, ES2, etc.). 1273
It is expected that external circuits receive a transient voltage of 1,5 kV 1274
peak with a waveform of 10/700s from sources outside the building. 1275
The expected transient is independent from the application (telecom; LAN 1276
or other). Therefore, it is assumed that for all kinds of applications the 1277
same transient appears. The value 1,5 kV 10/700s is taken from ITU-T 1278
K.21. 1279
It is expected that external circuits using earthed coaxial cable receive no 1280
transients that have to be taken into account from sources outside the 1281
building. 1282
Because of the earthed shield of the coaxial cable , a possible transient on 1283
the outside cable will be reduced at the earthed shield at the building 1284
entrance of the cable. 1285
It is expected that for external circuits within the same building no 1286
transients have to be taken into account. 1287
The transients for an interface are defined with respect to the terminals 1288
where the voltage is defined. For the majority of cases, the relevant 1289
voltages are common (Uc) and differential mode (Ud) voltages at the 1290
interface. For hand-held parts or other parts in extended contact with the 1291
human body, such as a telephone hand set, the voltage with respect to 1292
local earth (Uce) may be relevant. Figure 12 in this document shows the 1293
definition of the various voltages for paired -conductor interface. 1294
The transients for coaxial cable interfaces are between the centre 1295
conductor and shield (Ud) of the cable if the shield is earthed at the 1296
equipment. If the shield is isolated from earth at the equipment, then the 1297
shield-to-earth voltage (Us) is important. Earthing of the shield can consist 1298
of connection of the shield to the protective earthing, functional earth 1299
inside or immediately outside the equipment. It is assumed that all earths 1300
are bonded together. Figure 13 in this document shows the definition of the 1301
various voltages for coaxial-cable interfaces. 1302
An overview of insulation requirements is given in Table 6 in this document. 1303
IEC TR 62368-2:2019 © IEC 2019 – 41 –
1304
1305
1306
Figure 12 – Illustration of transient voltages on paired conductor external circuits 1307
– 42 – IEC TR 62368-2:2019 © IEC 2019
1308
1309
Figure 13 – Illustration of transient voltages on coaxial -cable external circuits 1310
Table 6 – Insulation requirements for external circuits 1311
External Circuit under consideration
Insulation Requirement
ES1 earthed None None
ES1 unearthed Separation (to floating metal parts and other floating ES1 circuits)
Electric strength test (using Table 15) between unearthed ES1 and other unearthed ES1 and floating parts
ES2 Basic insulation (to ES1 and metal parts)
Clearances; creepage distance; and solid insulation and by electric strength test (using Table 15) between ES2 and ES1 and metal parts
ES3 Double insulation or reinforced insulation (to ES1, ES2 and metal parts)
Clearances; creepage distance; and solid insulation requirements including electric strength test (using Table 15)
1312
Table 13 External circuit transient voltages 1313
Rationale: When the DC power distribution system is located outside the building, 1314
transient over-voltages can be expected. Transients are not present if the 1315
DC power system is connected to protective earthing and is located 1316
entirely within a single building. 1317
5.4.2.3.2.5 Determining transient voltage levels by measurement 1318
Source: Test method is taken from IEC 60950-1:2013, Annex G. 1319
5.4.2.3.4 Determining clearances using required withstand voltage 1320
Source: IEC 60664-1:2007, Table F.2 Case A (inhomogeneous field) and Case B 1321
(homogeneous field) 1322
IEC TR 62368-2:2019 © IEC 2019 – 43 –
Rationale: Values in Table 14 are taken from IEC 60664-1:2007 Table F.2 Case A 1323
(inhomogeneous field) and Case B (homogeneous field) and include explicit 1324
values for reinforced insulation . Clearances for reinforced insulation 1325
have been calculated in accordance with 5.1.6 of IEC 60664-1:2007. For 1326
reinforced insulation 5.1.6 states clearance shall be to the corresponding 1327
rated impulse voltage that is one step higher for voltages in the preferred 1328
series. For voltages that are not in the preferred series, the clearance 1329
should be based on 160 % of the required withstand voltage for basic 1330
insulation. 1331
When determining the required withstand voltage, interpolation should be 1332
allowed when the internal repetitive peak voltages are higher than the 1333
mains peak voltages, or if the required withstand voltage is above the 1334
mains transient voltage values. 1335
No values for PD 4 (pollution generates persistent conductivity) are 1336
included, as it is unlikely that such conditions are present when using 1337
products in the scope of the document. 1338
Table 14 Minimum clearances using required withstand voltage 1339
Rationale: IEC 62368-1 follows the rules and requirements of IEC basic safety 1340
publications, one of which is the IEC 60664 series. IEC 60664-1 specifies 1341
clearances for basic insulation and supplementary insulation. 1342
Clearances for reinforced insulation are not specified. Instead, 5.1.6 1343
specifies the rules for determining the reinforced clearances. 1344
The reinforced clearances in Table 14 have a varying slope, and include a 1345
“discontinuity”. The values of Table 14 are shown in Figure 14 in this 1346
document. 1347
1348
Figure 14 – Basic and reinforced insulation in Table 14 of IEC 62368-1:2018; 1349
ratio reinforced to basic 1350
– 44 – IEC TR 62368-2:2019 © IEC 2019
The brown line, reinforced clearance, is not a constant slope as is the 1351
yellow line, basic clearance. The ratio of reinforced to basic (blue line) 1352
varies from a maximum of 2:1 to a minimum of 1,49:1. Physically, this is not 1353
reasonable; the ratio should be nearly constant. 1354
In IEC 60664-1:2007, the values for basic insulation are given in Table 1355
F.2. No values are given for reinforced insulation. Table F.2 refers to 1356
5.1.6 for reinforced insulation. 1357
Rule 1, preferred series impulse withstand voltages 1358
Subclause 5.1.6 of IEC 60664-1:2007 states: 1359
“With respect to impulse voltages, clearances of reinforced insulation 1360
shall be dimensioned as specified in Table F.2 corresponding to the rated 1361
impulse voltage but one step higher in the preferred series of values in 1362
4.2.3 than that specified for basic insulation.” 1363
NOTE 1 IEC 62368-1 uses the term “required withstand voltage” instead of the 1364 IEC 60664-1 term “required impulse withstand voltage.” 1365
NOTE 2 IEC 62368-1 uses the term “mains transient voltage” instead of the IEC 60664-1 1366 term “rated impulse voltage.” 1367
The preferred series of values of rated impulse voltage acco rding to 4.2.3 1368
of IEC 60664-1:2007 is: 330 V, 500 V, 800 V, 1 500 V, 2 500 V, 4 000 V, 6 1369
000 V, 8 000 V, 12 000 V 1370
Applying Rule 1, the reinforced clearance (inhomogeneous field, pollution 1371
degree 2, Table F.2) for: 1372
– 330 V would be the basic insulation clearance for 500 V: 0,2 mm 1373
– 500 V would be the basic insulation clearance for 800 V: 0,2 mm 1374
– 800 V would be the basic insulation clearance for 1 500 V: 0,5 mm 1375
– 1 500 V would be the basic insulation clearance for 2 500 V: 1,5 mm 1376
– 2 500 V would be the basic insulation clearance for 4 000 V: 3,0 mm 1377
– 4 000 V would be the basic insulation clearance for 6 000 V: 5,5 mm 1378
– 6 000 V would be the basic insulation clearance for 8 000 V: 8,0 mm 1379
– 8 000 V would be the basic insulation clearance for 12 000 V: 14 mm 1380
– 12 000 V is indeterminate because there is no preferred voltage above 1381
12 000 volts. 1382
Rule 2, 160 % of impulse withstand voltages other than the preferred 1383
series 1384
With regard to non-mains circuits, subclause 5.1.6 of IEC 60664-1:2007 1385
states: 1386
“If the impulse withstand voltage required for basic insulation according to 1387
4.3.3.4.2 is other than a value taken from the preferred series, reinforced 1388
insulation shall be dimensioned to withstand 160 % of the value required 1389
for basic insulation.” 1390
The impulse withstand voltages other than the preferred series (in 1391
IEC 60664-1:2007, Table F.2) are: 400 V, 600 V, 1 200 V, 2 000 V, 3 000 1392
V, 10 000 V, and all voltages above 12 000 V. 1393
Applying Rule 2, the reinforced clearance (inhomogeneous field, pollution 1394
degree 2, Table F.2) for: 1395
400 V x 1,6 = 640 V interpolated to 0,20 mm. 1396
Since 640 V is not in the list, the reinforced insulation is determined by 1397
interpolation. Interpolation yields the reinforced clearance as 0,2 mm. 1398
IEC TR 62368-2:2019 © IEC 2019 – 45 –
Applying Rule 2 to the impulse withstand voltag es in Table F.2 that are not 1399
in the preferred series: 1400
– 400 V × 1,6 = 640 V interpolated to 0,20 mm 1401
– 600 V × 1,6 = 960 V interpolated to 0,24 mm 1402
– 1 200 V × 1,6 = 1 920 V interpolated to 0,92 mm 1403
– 2 000 V × 1,6 = 1 320 V interpolated to 2,2 mm 1404
– 3 000 V × 1,6 = 4 800 V interpolated to 3,8 mm 1405
– 10 000 V × 1,6 = 13 000 V interpolated to 19,4 mm 1406
– 15 000 V to 100 000 V × 1,6 and interpolated according to the rule. 1407
Clearance differences for Rules 1 and 2 1408
The two rules, Rule 1 for impulse withstand voltages o f the preferred 1409
series, and Rule 2 for impulse withstand voltages other than the preferred 1410
series, yield different clearances for the same voltages. These differences 1411
occur because the slope, mm/kV, of the two methods is slightly different. 1412
The slope for Rule 1 is not constant. The slope for Rule 2 is nearly 1413
constant. Figure 15 in this document illustrates the differences between 1414
Rule 1, Rule 2 and Table 14 of IEC 62368-1:2018. 1415
1416
Figure 15 – Reinforced clearances according to Rule 1, Rule 2 , and Table 14 1417
If the two values for Rules 1 and 2 are combined into one set of values, the 1418
values are the same as in existing Table 14 (the brown line in Figure 14 1419
and Figure 15 in this document). According to IEC 60664-1:2007, 5.1.6, 1420
only the impulse withstand voltages “other than a value taken from the 1421
preferred series…” are subject to the 160 % rule. Therefore, the 1422
clearances jump from Rule 1 criteria to Rule 2 criteria and back again. This 1423
yields the radical slope changes of the Table 14 reinforced clearances 1424
(brown) line. 1425
Rule 1
Rule 2
Basic insulation
Table 15
– 46 – IEC TR 62368-2:2019 © IEC 2019
Physically, the expected reinforced insulation clearances should be a 1426
constant proportion of the basic insulation clearances. However, the 1427
proportion between steps of Rule 1 (preferred series of impulse withstand 1428
voltages) are: 1429
– 330 V to 500 V: 1,52 1430
– 500 V to 800 V: 1,60 1431
– 800 V to 1 500 V: 1,88 1432
– 1 500 V to 2 500 V: 1,67 1433
– 2 500 V to 4 000 V: 1,60 1434
– 4 000 V to 6 000 V: 1,50 1435
– 6 000 V to 8 000 V: 1,33 1436
– 8 000 V to 12 000 V: 1,50 1437
Average proportion, 330 to 12 000: 1,57 1438
For Rule 2, all of the clearances for reinforced insulation are based on 1439
exactly 1,6 times the non-preferred series impulse withstand voltage for 1440
basic insulation. 1441
The two rules applied in accordance with 5.1.6 of IEC 60664-1:2007 result 1442
in the variable slope of the clearance requirements for reinforced 1443
insulation of IEC 62368-1. 1444
IEC TC 108 noted that, if the rules of IEC 60664-1 are followed, for 1445
clearances for reinforced insulation , some values were more than double 1446
the requirements for basic insulation. IEC TC 108 felt that this should not 1447
be the case and decided to limit the requirement for reinforced insulation 1448
to twice the value of basic insulation, thereby deviating from IEC 60664-1. 1449
In addition, normal rounding rules were applied to the values in the table. 1450
5.4.2.4 Determining the adequacy of a clearance using an electric strength test 1451
Source: IEC 60664-1:2007, Table F.5 1452
Purpose: Tests are carried out by either impulse voltage or AC voltage with the 1453
values of Table 15. 1454
Rationale: The impulse test voltages in Table 15 are taken from IEC 60664-1:2007, 1455
Table F.5. The calculation for the AC RMS. values as well as the DC values 1456
are based on the values given in Table A.1 of IEC 60664-1:2007 (see 1457
Table 7 in this document for further explanation). 1458
This test is not suited for homogenous fields. This is for an actual design 1459
that is within the limits of the homogenous and inhomogeneous field. 1460
Calculations for the voltage drop across an air gap during the electric 1461
strength test may be rounded up to the next higher 0,1 mm increment. In 1462
case the calculated value is higher than the value in the next row, the next 1463
row may be used. 1464
Enamel Material: Most commonly used material is polyester resin or 1465
polyester 1466
Dielectric constant for Polyester: 5 (can vary) 1467
Dielectric constant for air: 1 1468
Formula used for calculation (voltage divides inversely proportional to the 1469
dielectric constant) 1470
Transient = 2 500 V = 2 500 ( thickness of enamel / 5 + air gap / 1) = 2 500 1471
(0,04 / 5 + 2 / 1 for 2 mm air gap) = 2 500 (0,008 + 2) = (10 V across 1472
enamel + 2 490 V across air gap) 1473
IEC TR 62368-2:2019 © IEC 2019 – 47 –
Related to condition a of Table 15, although U is any required withstand 1474
voltage higher than 12,0 kV, there is an exception when using Table F.5 of 1475
IEC 60664-1:2007. 1476
Table 7 – Voltage drop across clearance and solid insulation in seri es 1477
Enamel thickness
mm
Air gap
mm
Transient on 240 V system
Transient voltage
across air gap
Transient voltage across enamel
Peak impulse
test voltage for
2 500 V peak
transient from
Table 16
Test voltage
across air gap
Test voltage across enamel
Material: Polyester, dielectric constant = 5
0,04 2 2 500 2 490 10 2 950 12 2 938
0,04 1 2 500 2 480 20 2 950 24 2 926
0,04 0,6 2 500 2 467 33 2 950 39 2 911
For 2 500 V peak impulse (transient for 230 V system), the homogenous field distanc e is 0,6 mm (from Table A.1 of IEC 60664-1:2007). Our test voltage for 2 500 V peak is 2 950 V peak from Table 15. This means that a minimum distance of 0,79 mm through homogenous field needs to be maintained to pass the 2 950 V impulse test.
This gives us a margin of (0,19 /0,6) 100 = 3,2 %. In actual practice, the distance will be higher as it is not a true homogenous field. Therefore, we do not need to verify compliance with Table 14. We are always on the conservative side.
Material: Polyamide, dielectric constant = 2,5
0,04 2 2 500 2 480 20 2 950 23 2 927
0,04 1 2 500 2 460 40 2 950 46 2 904
0,04 0,6 2 500 2 435 65 2 950 76 2 874
For 2 500 V peak impulse (transient for 230 V system), the homogenous field distance is 0,6 mm (from Table A.1 of IEC 60664-1:2007). Our test voltage for 2 500 V peak is 2 950 V peak from Table 15. This means that a minimum distance of 0,78 mm through homogenous field needs to be maintained to pass the 2 950 V impulse test.
This gives us a margin of (0,18/0,6) 100 = 3,0 %. In actual practice, the distance will be higher , as it is not a true homogenous field. Therefore, we do not need to verify compliance with Table 14. We are always on the consevative side.
1478
5.4.2.5 Multiplication factors for altitudes higher than 2 000 m above sea level 1479
Source: IEC 60664-1:2007, curve number 2 for case A using impulse test. 1480
Purpose: Test is carried out by either impulse voltage or AC voltage with the values 1481
of Table 16 and the multiplication factors for altitudes higher than 2 000 m. 1482
Rationale: Table 16 is developed using Figure A.1 of IEC 60664-1:2007, curve number 1483
2 for case A using impulse test. 1484
5.4.2.6 Compliance criteria 1485
Source: IEC 60664-1:2007, 5.1.1 1486
Rationale: IEC 62368-1:2018, Annex O figures are similar/identical to figures in 1487
IEC 60664-1:2007. 1488
Tests of IEC 62368-1:2018, Annex T simulate the occurrence of mechanical 1489
forces: 1490
– 10 N applied to components and parts that may be touched during 1491
operation or servicing. Simulates the accidental contact with a finger or 1492
part of the hand; 1493
– 30 N applied to internal enclosures and barriers that are accessible to 1494
ordinary persons. Simulates accidental contact of part of the hand ; 1495
– 48 – IEC TR 62368-2:2019 © IEC 2019
– 100 N applied to external enclosures of transportable equipment and 1496
handheld equipment. Simulates expected force applied durin g use or 1497
movement; 1498
– 250 N applied to external enclosures (except those covered in T.4). 1499
Simulates expected force applied by a body part to the surface of the 1500
equipment. It is not expected that such forces will be applied to the 1501
bottom surface of heavy equipment ( 18 kg). 1502
During the force tests metal surfaces shall not come into contact with parts 1503
at ES2 or ES3 voltage. 1504
5.4.3 Creepage distances 1505
Source: IEC 60664-1:2007, 3.3 1506
Purpose: To prevent flashover along a surface or breakdown of the insulation. 1507
Rationale: Preserve safeguard integrity. 1508
In IEC 60664-1:2007, Table F.4 columns 2 and 3 for printed wiring boards 1509
are deleted, as there is no rationale for the very small creepage distances 1510
for printed wiring in columns 2 and 3 (the only rationale is that it is in the 1511
basic safety publication IEC 60664-1). 1512
However, there is no rationale why the creepage distances are different 1513
for printed wiring boards and other isolation material under the same 1514
condition (same PD and same CTI) . 1515
Moreover the creepage distances for printed boards in columns 2 and 3 1516
are in conflict with the requirements in G.13.3 (Coated printed boards). 1517
Consequently the values for voltages up to 455 V in Table G.16 were 1518
replaced. 1519
Creepage distances between the outer insulating surface of a connect or 1520
and conductive parts at ES3 voltage level shall comply with the 1521
requirements of basic insulation only, if the connectors are fixed to the 1522
equipment, located internal to the outer electrical enclosure of the 1523
equipment, and are accessible only after removal of a sub-assembly which 1524
is required to be in place during normal operation. 1525
It is assumed that the occurrence of both factors, the sub -assembly being 1526
removed, and the occurrence of a transient overvoltage have a reduced 1527
likelihood and hazard potential. 1528
5.4.3.2 Test method 1529
Source: IEC 60664-1:2007, 3.2 1530
Purpose: Measurement of creepage distance. 1531
Rationale: To preserve safeguard integrity after mechanical tests . 1532
Annex O figures are similar/identical to figures in IEC 60950-1 and 1533
IEC 60664-1. 1534
Tests of Annex T simulate the occurrence of mechanical forces: 1535
– 10 N applied to components and parts that are likely to be touched by a 1536
skilled person during servicing, where displacement of the part reduces 1537
the creepage distance. Simulates the accidental contact wi th a finger or 1538
part of the hand. 1539
– 30 N applied to internal enclosures and barriers that are accessible to 1540
ordinary persons. Simulates accidental contact of part of the hand. 1541
– 100 N applied to external enclosures of transportable equipment and 1542
hand-held equipment. Simulates expected force applied during use or 1543
movement. 1544
IEC TR 62368-2:2019 © IEC 2019 – 49 –
– 250 N applied to external enclosures (except those covered in T.4). 1545
Simulates expected force when leaning against the equipment surface. It 1546
is not expected that such forces will be applie d to the bottom surface of 1547
heavy equipment ( 18 kg). 1548
Creepage distances are measured after performing the force tests of 1549
Annex T. 1550
5.4.3.3 Material group and CTI 1551
Source: IEC 60112 1552
Rationale: Classification as given in IEC 60112. 1553
5.4.3.4 Compliance criteria 1554
Source: IEC 60664-1:2007, Table F.4; IEC 60664-4 for frequencies above 30 kHz 1555
Rationale: Values in Table 17 are the same as in Table F.4 of IEC 60664-1:2007. 1556
Values in Table 18 are the same as in Table 2 of IEC 60664-4:2005 and 1557
are used for frequencies up to 400 kHz . 1558
5.4.4 Solid insulation 1559
Source: IEC 60950-1, IEC 60664-1 1560
Purpose: To prevent breakdown of the solid insulation. 1561
Rationale: To preserve safeguards integrity. 1562
Exclusion of solvent based enamel coatings for safety insulations are 1563
based on field experience. However, with the advent of n ewer insulation 1564
materials those materials may be acceptable in the future when passing the 1565
adequate tests. 1566
Except for printed boards (see G.13), the solid insulation shall meet the 1567
requirements of 5.4.4.4 to 5.4.4.7 as applicable. 1568
5.4.4.2 Minimum distance through insulation 1569
Source: IEC 60950-1:2005 1570
Purpose: Minimum distance through insulation of 0,4 mm for supplementary 1571
insulation and reinforced insulation. 1572
Rationale: Some (very) old documents required for single insulations 2 mm dti 1573
(distance through insulation) for reinforced insulation and 1 mm for 1574
supplementary insulation. If this insulation served also as outer 1575
enclosure for Class II equipment, it had to be mechanically robust, which 1576
was tested with a hammer blow of 0,5 Nm. 1577
The wire documents did not distinguish between grades of insulation, and 1578
required 0,4 mm for PVC insulation material. This value was considered 1579
adequate to protect against electric shock when touching the insulation if it 1580
was broken. This concept was also introduced in VDE 0860 (w hich evolved 1581
into IEC 60065), where the 0,4 mm value was discussed first. For IT 1582
products this value was first only accepted for in accessible insulations. 1583
The VDE document for telecom equipment (VDE 0804) did not include any 1584
thickness requirements, but the insulation had to be adequate for the 1585
application. 1586
The document VDE 0730 for household equipment with electric motors 1587
introduced in 1976 the requirement of an insulation thickness of 0,5 mm 1588
between input and output windings of a transformer. This was i ntroduced 1589
by former colleagues from IBM and Siemens (against the position of the 1590
people from the transformer committee). 1591
– 50 – IEC TR 62368-2:2019 © IEC 2019
Also VDE 0110 (Insulation Coordination, which evolved into the IEC 60664 1592
series) contained a minimum insulation thickness of 0,5 mm fo r 250 V 1593
supply voltage, to cover the effect of insulation breakage. 1594
These 0,5 mm then evolved into 0,4 mm (in IEC 60950-1), with the 1595
reference to VDE 0860 (IEC 60065), where this value was already in use. 1596
It is interesting to note that the 0,31 mm which is derived from Table 2A of 1597
IEC 60950-1, has also a relation to the 0,4 mm. 0,31 mm is the minimum 1598
value of the average insulation thickness of 0,4 mm, according to experts 1599
from the wire manufacturers. 1600
5.4.4.3 Insulating compound forming solid insulation 1601
Source: IEC 60950-1 1602
Purpose: Minimum distance through insulation of 0,4 mm for supplementary 1603
insulation and reinforced insulation. 1604
Rationale: The same distance through insulation requirements as for solid insulation 1605
apply (see 5.4.4.2). Insulation is subjected to thermal cycling (see 1606
5.4.1.5.3), humidity test (see 5.4.8) and electric strength test (see 5.4.9). 1607
Insulation is inspected for cracks and voids . 1608
5.4.4.4 Solid insulation in semiconductor devices 1609
Source: IEC 60950-1, UL 1577 1610
Purpose: No minimum thickness requirements for the solid insulation. 1611
Rationale: – type test ing of 5.4.9.1 (electric strength testing at 160 % of the normal 1612
value after thermal cycling and humidity conditioning), and routine 1613
electric strength test of 5.4.9.2 has been used for many years, especially 1614
in North America. 1615
– refers to G.12, which references IEC 60747-5-5. 1616
5.4.4.5 Insulating compound forming cemented joints 1617
Source: IEC 60950-1 1618
Rationale: a) The distances along the path comply with PD 2 requirements 1619
irrespective of the joint; 1620
b) applies if protected to generate PD 1 environment ; 1621
c) applies if treated like solid insulation environment, no clearances and 1622
creepage distances apply; 1623
d) is not applied to printed boards, when the board temperature is below 1624
90 °C, as the risk for board delaminating at lower temperatures is 1625
considered low. 1626
Optocouplers are excluded from the requirements of this subclause, 1627
because the document requires optocouplers to comply with 1628
IEC 60747-5-5, which sufficiently covers cemented joints . 1629
IEC TR 62368-2:2019 © IEC 2019 – 51 –
5.4.4.6.1 General requirements 1630
Source: IEC 60950-1, IEC 61558-1:2005 1631
Rationale: No dimensional or constructional requirements for insulation in thin sheet 1632
material used as basic insulation, is aligned to the requirements of 1633
IEC 61558-1. 1634
Two or more layers with no minimum thickness are required for 1635
supplementary insulation or reinforced insulation , provided they are 1636
protected against external mechanical influences. 1637
Each layer is qualified for the full voltage for supplementary insulation or 1638
reinforced insulation. 1639
The requirements are based on extensive tests performed on thin sheet 1640
material by manufacturers and test houses involved in IEC TC 74 (now IEC 1641
TC 108) work. 1642
5.4.4.6.2 Separable thin sheet material 1643
Source: IEC 60950-1 1644
Rationale: For two layers, test each layer with the electric strength test of 5.4.9 for the 1645
applicable insulation grade. For three layers, test all combinations of two 1646
layers together with the electric strength test of 5.4.9 for the applicable 1647
insulation grade. 1648
Each layer is qualified for the full voltage for supplementary insulation or 1649
reinforced insulation. 1650
The requirements are based on extensive tests performed on thin sheet 1651
material by manufacturers and test houses involved in IEC TC 74 (now IEC 1652
TC 108) work. 1653
5.4.4.6.3 Non-separable thin sheet material 1654
Source: IEC 60950-1 1655
Rationale: For testing non-separable layers, all the layers are to have the same 1656
material and thickness. If not, samples of different materials are tested as 1657
given in 5.4.4.6.2 for separable layers. When testing non-separable layers, 1658
the principle used is the same as for separable layers. 1659
When testing two separable layers, each layer is tested for the required 1660
test voltage. Two layers get tested for two times the required test voltage 1661
as each layer is tested for the required test voltage. When testing two non -1662
separable layers, the total test voltage remain s the same, for example, two 1663
times the required test voltage. Therefore, two non -separable layers are 1664
tested at 200 % of the required test voltage. 1665
When testing three separable layers, every combination of two layers is 1666
tested for the required test voltage. Therefore, a single layer gets tested for 1667
half the required test voltage and three layers are tested for 150 % of the 1668
required test voltage. 1669
5.4.4.6.4 Standard test procedure for non-separable thin sheet material 1670
Source: IEC 60950-1 1671
Rationale: Test voltage 200 % of Utest if two layers are used. 1672
Test voltage 150 % of Utest if three or more layers are used. 1673
See the rationale in 5.4.4.6.3. The procedure can be applied to both 1674
separable and non-separable layers as long as the material and material 1675
thickness is same for all the layers. 1676
– 52 – IEC TR 62368-2:2019 © IEC 2019
5.4.4.6.5 Mandrel test 1677
Source: IEC 61558-1:2005, 26.3.3; IEC 60950-1:2013; IEC 60065:2011 1678
Purpose: This test should detect a break of the inner layer of non-separated foils. 1679
Rationale: This test procedure is taken from IEC 61558-1, 26.3.3, and the test voltage 1680
is 150 % Utest, or 5 kV RMS., whatever is greater. 1681
5.4.4.7 Solid insulation in wound components 1682
Source: IEC 60950-1, IEC 61558-1 1683
Purpose: To identify constructional requirements of insulation of winding wires and 1684
insulation between windings . 1685
Rationale: Requirements have been used in IEC 60950-1 for many years and are 1686
aligned to IEC 61558-1. 1687
Planar transformers are not considered wound components and have to 1688
comply with G.13. 1689
5.4.4.9 Solid insulation requirements at frequencies higher than 30 kHz 1690
Source: IEC 60664-4:2005 1691
Purpose: To identify requirements for solid insulation that is exposed to voltages at 1692
frequencies above 30 kHz. 1693
Rationale: The requirements are taken from the data presented in Annex C of 1694
IEC 60664-4:2005. Testing of solid insulation can be performed at line 1695
frequency as detailed in 6.2 of IEC 60664-4:2005. 1696
In general, the breakdown electric field strength of insulation can be 1697
determined according to IEC 60243-1 (Electrical strength of insulating 1698
materials−Test methods−Part 1) as referred from 5.3.2.2.1 of IEC 60664-1699
1:2007 (see below). 1700
5.3.2.2.1 Frequency of the voltage 1701
The electric strength is greatly influenced by the frequency of the applied 1702
voltage. Dielectric heating and the probability of thermal instability increase 1703
approximately in proportion to the frequency. The breakdown field strength 1704
of insulation having a thickness of 3 mm when measured at power 1705
frequency according to IEC 60243-1 is between 10 kV/mm and 40 kV/mm. 1706
Increasing the frequency will reduce the electric strength of most insulating 1707
materials. 1708
NOTE The influence of frequencies greater than 30 kHz on the electric strength is 1709 described in IEC 60664-4. 1710
Table 20 shows the electric field strength for some commonly used 1711
materials. These values are related to a frequency of 50/60 Hz. 1712
Table 21, which is based on Figure 6 of IEC 60664-4:2005, shows the 1713
reduction factor for the value of breakdown electric field strength at higher 1714
frequencies. The electric field strength of materials drops differently at 1715
higher frequencies. The reduction of the insulation prope rty is to be 1716
considered when replacing the calculation method by the alternative ES 1717
test at mains frequency, as shown after the sixth paragraph of 5.4.4.9. 1718
Table 21 is for materials of 0,75 mm in thickness or more. Table 22 is for 1719
materials of less than 0,75 mm in thickness. 1720
The 1,2 times multiplier comes from IEC 60664-4:2005, subclause 7.5.1, 1721
where the partial discharge (PD) extinction voltage must include a safety 1722
margin of 1,2 times the highest peak periodic voltage. 1723
IEC TR 62368-2:2019 © IEC 2019 – 53 –
5.4.5 Antenna terminal insulation 1724
Source: IEC 60065 1725
Purpose: To prevent breakdown of the insulation safeguard. 1726
Rationale: The insulation shall be able to withstand surges due to overvoltages 1727
present at the antenna terminals. These overvoltages are caused by 1728
electrostatic charge build up, but not from lightning effects. A maximum 1729
voltage of 10 kV is assumed. The associated test of G.10.4 simulates this 1730
situation by using a 10 kV test voltage discharged over a 1 nF capacitor. 1731
5.4.6 Insulation of internal wire as a part of a supplementary safe guard 1732
Source: IEC 60950-1 1733
Purpose: To specify constructional requirements of accessible internal wiring 1734
Rationale: Accessible internal wiring isolated from ES3 by basic insulation only 1735
needs a supplementary insulation. If the wiring is reliably routed away so 1736
that it will not be subject to handling by the ordinary person, then smaller 1737
than 0,4 mm thick supplementary insulation has been accepted in 1738
IEC 60950-1. But the insulation still has to have a certain minimum 1739
thickness together with electric strength withstand capability. The given 1740
values have been successfully used in products covered by this document 1741
for many years (see Figure 16 in this document). 1742
1743
Figure 16 – Example illustrating accessible internal wiring 1744
– 54 – IEC TR 62368-2:2019 © IEC 2019
5.4.7 Tests for semiconductor components and for cemented joints 1745
Source: IEC 60950-1 1746
Purpose: To simulate lifetime stresses on adjoining materials. 1747
To detect defects by applying elevated test voltages after sample 1748
conditioning. 1749
To avoid voids, gaps or cracks in the insulating material and delaminating 1750
in the case of multilayer printed boards. 1751
Rationale: This method has been successfully used for products in the scope of this 1752
document for many years. 1753
5.4.8 Humidity conditioning 1754
Source: IEC 60950-1 and IEC 60065. Alternative according to IEC 60664-1:2007, 1755
6.1.3.2 1756
Purpose: Material preparations for dielectric strength test . Prerequisite for further 1757
testing. 1758
A tropical climate is a location where it is expected to have high 1759
temperatures and high humidity during most of the year. The document 1760
does not indicate what levels of temperature or humidity constitute a 1761
tropical climate. National authorities define whether their country requires 1762
products to comply with tropical requirements. Only a few countries, such 1763
as Singapore and China, have indicated in the CB scheme that they require 1764
such testing. 1765
5.4.9 Electric strength test 1766
Source: IEC 60664-1: 2007 1767
Purpose: To test the insulation to avoid breakdown. 1768
Rationale: Values of test voltages are derived from Table F.5 of IEC 60664-1:2007, 1769
however the test duration is 60 s. 1770
This method has been successfully used for products in the scope of 1771
IEC 60065 and IEC 60950-1 for many years. 1772
The DC voltage test with a test voltage equal to the peak value of the AC 1773
voltage is not fully equivalent to the AC voltage test due to the different 1774
withstand characteristics of solid insulation for these types of voltages. 1775
However in case of a pure DC voltage stress, the DC voltage test is 1776
appropriate. To address this situation the DC test is made with both 1777
polarities. 1778
Table 25 Test voltages for electric strength tests based on transient voltages 1779
Source: IEC 60664-1:2007 1780
Rationale: To deal with withstand voltages and cover transients. 1781
The basic insulation and supplementary insulations are to withstand a 1782
test voltage that is equal to the transient peak voltage. The test voltage for 1783
the reinforced insulation shall be equal to the transient in the next in the 1784
preferred series. According to 5.1.6 of IEC 60664-1:2007, the use of 160 % 1785
test value for basic insulation as the test value for reinforced insulation 1786
is only applicable if other values than the preferred series are used. 1787
Functional insulation is not addressed, as is it presumed not to provide 1788
any protection against electric shock. 1789
IEC TR 62368-2:2019 © IEC 2019 – 55 –
Table 26 Test voltages for electric strength tests based on the peak of the working 1790
voltages and recurring peak voltages 1791
Source: IEC 60664-1:2007 1792
Rationale: Column B covers repetitive working voltages and requires higher test 1793
voltages due to the greater stress to the insulation. 1794
Recurring peak voltages ( IEC 60664-1:2007, 5.3.3.2.3) need to be 1795
considered, when they are above the temporary overvoltage values, or in 1796
circuits separated from the mains. 1797
If the recurring peak voltages are above the temporary overvoltage 1798
values, these voltages have to be used, multiplied by the factor given in 1799
IEC 60664-1:2007, 5.3.3.2.3. 1800
Table 27 Test voltages for electric strength tests based on temporary overvoltages 1801
Source: IEC 60664-1:2007 1802
Rationale: Temporary overvoltages (IEC 60664-1:2007, 5.3.3.2.2) need to be 1803
considered as they may be present up to 5 s. The test voltage for 1804
reinforced insulation is twice the value of basic insulation . 1805
5.4.10 Safeguards against transient voltages from e xternal circuits 1806
Source: IEC 62151:2000, Clause 6 1807
Purpose: To protect persons against contact with external circuits subjected to 1808
transients (for example, telecommunication networks). 1809
Rationale: External circuits are intended to connect the equipment to other 1810
equipment. Connections to remote equipment are made via communication 1811
networks, which could leave the building. Examples for such 1812
communication networks are telecommunication networks and Ethernet 1813
networks. The operating voltages of communication netwo rks are usually 1814
within the limits of ES1 ( for example, Ethernet) or within the limits of ES2 1815
(for example, telecommunication networks). 1816
When leaving the buildings, communication networks may be subjected to 1817
transient overvoltages due to atmospheric dischar ges and faults in power 1818
distribution systems. These transients are depending on the infrastructure 1819
of the cables and are independent on the operating voltage of the 1820
communication network. The expected transients on telecommunication 1821
networks are specified in ITU-T recommendations. The transient value in 1822
Table 13 ID 1 is taken from ITU-T K.21 as 1,5 kV 10/700 µs (terminal 1823
equipment). This transient of 1,5 kV 10/700 µs does not cause a hazardous 1824
electric shock, but it is very uncomfortable to persons effectin g by such a 1825
transient. To avoid secondary hazards a separation between an external 1826
circuit connected to communication networks subjected transients is 1827
required. 1828
Because the transient does not cause a hazardous electric shock the 1829
separation element needs not to be a reinforced safeguard nor a basic 1830
safeguard in the meaning of IEC 62368-1. It is sufficient to provide a 1831
separation complying with an electric strength test, only. Therefore for this 1832
separation no clearance, no creepage distances and no thickness 1833
requirements for solid insulation are required. 1834
The separation is required between the external circuit subjected to 1835
transients and all parts, which may accessible to ordinary persons or 1836
instructed persons. 1837
– 56 – IEC TR 62368-2:2019 © IEC 2019
The likelihood a transient occurs and a body cont act with an accessible 1838
part occurs at the same time increases with the contact time. Therefore 1839
non-conductive parts and unearthed parts of the equipment maintained in 1840
continuous contact with the body during normal use ( for example, a 1841
telephone handset, head set, palm rest surfaces) the separation should 1842
withstand a higher test voltage. 1843
Two test procedures for the electric strength test are specified in 5.4.10.2. 1844
5.4.10.2.2 Impulse test 1845
The impulse test is performing an impulse test by using the impulse 1846
generator for the 10/700 µs impulse (see test generator D.1 of Annex D). 1847
With the recorded waveforms it could be judged whether a breakdown of 1848
insulation has occurred, or if the surge suppression device has worked 1849
properly. 1850
The examples in Figure 17, Figure 18, 1851
1 – gas discharge type
2 – semiconductor type
3 – metal oxide type
Consecutive impulses are identical in their waveforms.
1852
Figure 19 and Figure 20 in this document could be used to assist in judging whether or not 1853
a surge suppressor has operated or insulation has broken down. 1854
1855
Consecutive impulses are identical in their waveforms.
1856
Figure 17 – Waveform on insulation without surge suppressors and no breakdown 1857
IEC TR 62368-2:2019 © IEC 2019 – 57 –
Consecutive impulses are not identical in their waveforms. The pulse shape changes from pulse to pulse until a stable resistance path through the insulation is established. Breakdown can be seen clearly on the shape of the pulse voltage oscillogram.
1858
Figure 18 – Waveforms on insulation during breakdown without surge suppressors 1859
1 – gas discharge type
2 – semiconductor type
3 – metal oxide type
Consecutive impulses are identical in their waveforms.
1860
Figure 19 – Waveforms on insulation with surge suppressors in operation 1861
1862
Figure 20 – Waveform on short-circuited surge suppressor and insulation 1863
– 58 – IEC TR 62368-2:2019 © IEC 2019
5.4.10.2.3 Steady-state test 1864
The steady-state test is performing an electric strength test according to 1865
5.4.9.1. This test is simple test with an RMS voltage. But if for example, 1866
surge suppressors are used to reduce the transients from the external 1867
circuits within the equipment this RMS test may by not adequate. In this 1868
case an impulse test is more applicable. 1869
5.4.11 Separation between external circuits and earth 1870
Source: IEC 62151:2000, 5.3 1871
Purpose: To protect persons working on communication networks, and users of other 1872
equipment connected to the network from hazards in the equipment. 1873
Rationale: Class I equipment provides basic insulation between mains and earthed 1874
conductive parts and requires the conductive parts to be connected to a PE 1875
conductor that has to be connected to the earthing terminal in the buildings 1876
installation to be safe to use. In an isolated environment such an earth 1877
terminal is not present in the building installation. Nevertheless the use of 1878
class I equipment in such an isolated environment is still safe to use, 1879
because in case of a breakdown of the insulation in the equipment (fault of 1880
basic insulation) the second barrier is provided by the isolated 1881
environment (similar to a supplementary insulation). 1882
With the connection of the equipment via an external circuit to a 1883
communication network from outside the building installation to a remote 1884
environment the situation will change. It is unknown whether the remote 1885
environment is an isolated or non-isolated environment. During and after a 1886
fault of the basic insulation in a class I equipment (from mains to 1887
conductive parts) installed in an isolated installation (non -earthed 1888
installation) the conductive parts will become live ( mains potential). If now 1889
the conductive parts are not separated from the external circuit, the 1890
mains voltage will be transferred to the remote installation via the 1891
communication network. This is a hazardous situation in the remote 1892
environment and can be dangerous for persons in that remote environment. 1893
Also in old building installations socket outlet s exist with no earth contact. 1894
This situation will not be changed in the near future. 1895
To provide protection for those situations, a separation between an 1896
external circuit intended to be connected to communication networks 1897
outside the building (for example, telecommunication networks) and a 1898
separation between the external circuit and earthed parts is required. 1899
For this separation, it is sufficient to comply with the requirements of 1900
5.4.11.2 tested in accordance with 5.4.11.3. For this separation, no 1901
clearance, no creepage distances and no thickness requirements for 1902
solid insulation is required. 1903
5.5 Components as safeguards 1904
Rationale: For failure of a safeguard and a component or device that is not a 1905
safeguard: 1906
Safeguard failure: A failure is considered to be a safeguard failure if the 1907
part itself or its function, during normal operating conditions , contributes 1908
to change an ES class to a lower ES class. In this case, the part is 1909
assessed for its reliability by applying the applicable safeguard component 1910
requirements in 5.5 and the associated requirements in Annex G. When 1911
establishing ES1, ES2 limits apply during single fault condition of these 1912
parts. In case no requirements for the component are provided in 5.5 or 1913
Annex G, the failure is regarded as a non-safeguard failure. 1914
IEC TR 62368-2:2019 © IEC 2019 – 59 –
Non-safeguard failure: A failure is considered to be a non -safeguard 1915
failure if the part itself or its function, under normal operating conditions , 1916
does not contribute to change an ES class to a lower ES Class. In this 1917
case, there is no need to assess the reliability of the part. When 1918
establishing ES1, ES1 limits apply for the single fault condition of these 1919
parts. Where applicable, 5.3.1 applies. Figure 21 and Figure 22 in this 1920
document give practical examples of the requirements when ordin ary 1921
components bridge insulation. 1922
Example 1 1923
1924
Figure 21 – Example for an ES2 source 1925
A single fault of any component or part may not result in the accessible 1926
part exceeding ES1 levels, unless the part complies with the requirements 1927
for a basic safeguard. 1928
The basic safeguard in parallel with the part(s) is to comply with: 1929
– the creepage distance requirements; and 1930
– the clearance requirements 1931
for basic insulation. 1932
There are no other requirements for the components or parts if the 1933
accessible part remains at ES1. 1934
Example 2 1935
1936
Figure 22 – Example for an ES3 source 1937
A single fault of any component or part may not result in the accessible 1938
part exceeding ES1 levels, unless the parts comply with the requirements 1939
for a double or reinforced safeguard. 1940
– 60 – IEC TR 62368-2:2019 © IEC 2019
The double or reinforced safeguard in parallel with the part(s) is to comply 1941
with: 1942
– the creepage distance requirements; and 1943
– the clearance requirements, 1944
for double insulation or reinforced insulation. 1945
There are no other requirements for the components or parts if the 1946
accessible part remains at ES1. 1947
5.5.2.1 General requirements 1948
Source: Relevant IEC component documents 1949
Purpose: The insulation of components has to be in compliance with the relevant 1950
insulation requirements of 5.4.1, or with the safety requirements of the 1951
relevant IEC document. 1952
Rationale: Safety requirements of a relevant document are accepted if they are 1953
adequate for their application, for example, Y2 capacitors of IEC 60384-14. 1954
5.5.2.2 Capacitor discharge after disconnection of a connector 1955
Source: IEC TS 61201:2007, Annex A 1956
Rationale: The 2 s delay time represents the typical access time after disconnecting a 1957
connector. When determining the accessible voltage 2 s after 1958
disconnecting a connector, the tolerance of the X capacitor is not 1959
considered. 1960
If a capacitor is discharged by a resistor ( for example, a bleeder resistor), 1961
the correct value of the resistor can be calculated using the following 1962
formula: 1963
R = (2 / C) x [1 / ln(E / Emax)] M 1964
where: 1965
C is in microfarads 1966
E is 60 for an ordinary person or 120 for an instructed person 1967
Emax is the maximum charge voltage or mains peak voltage 1968
ln is the natural logarithm function 1969
NOTE 1 When the mains is disconnected, the capacitance is comprised of both the X 1970 capacitors and the Y capacitors, and other possible capacitances. The circuit is analyzed to 1971 determine the total capacitance between the poles of the connector or plug. 1972
NOTE 2 If the equipment rated mains voltage is 125 V, the maximum value of the 1973 discharge resistor is given by : 1974
R = 1,85 / C M 1975
NOTE 3 If the equipment rated mains voltage is 250 V, the maximum value of the 1976 discharge resistor is given by : 1977
R = 1,13 / C M 1978
NOTE 4 The absolute value of the above calculations is used for the discharge resistor 1979 value. 1980
The test method includes a maximum time error of about 9% less than the 1981
calculated time for a capacitive discharge. This error was deemed 1982
acceptable for the sake of consistency with past practice. 1983
For measuring the worst case, care should be taken that t he discharge is 1984
measured while at the peak of the input voltage. To ensure this, an 1985
automatic control system that switches off at the peak voltage can be used. 1986
IEC TR 62368-2:2019 © IEC 2019 – 61 –
A method used by several other documents, such as IEC 60065 and 1987
IEC 60335-1 is to repeat the measurement 10 times and record the 1988
maximum value. This assumes that one of the 10 measurements will be 1989
sufficiently close to the peak value. 1990
Another possibility might be to use an oscilloscope during the 1991
measurement, so one can see if the measurement was don e near the 1992
maximum. 1993
Single fault conditions need not be considered if the component complies 1994
with the relevant component requirements of the document. For example, a 1995
resistor connected in parallel with a capacitor where a capacitor voltage 1996
becomes accessible upon disconnection of a connector, need not be 1997
faulted if the resistor complies with 5.5.6. 1998
When determining the accessible voltage 2 s after disconnection of the 1999
connector, the tolerance of the X-capacitor is not considered. 2000
5.5.6 Resistors 2001
Source: IEC 60950-1 and IEC 60065 2002
Rationale: When a group of resistors is used, the resistors are in series. The whole 2003
path consists of the metal lead and helical end (metal) and resistor body. 2004
The clearance and creepage distance is across the resistor body only. 2005
The total path then consists of conductive metal paths and resistor bodies 2006
(all in series). In this case, Figure O.4 becomes relevant when you want to 2007
determine the total clearance and creepage distance. 2008
5.5.7 SPDs 2009
Rationale: See Attachment A for background information on the use of SPD’s . 2010
It should be noted that the issue is still under discussion in IEC TC 108. 2011
The rationale will be adapted as soon as the discussion is finalized. 2012
A GDT is a gap, or a combination of gaps, in an enclosed discharge 2013
medium other than air at atmospheric pressure, and designed to protect 2014
apparatus or personnel, or both, from high transient voltages (from ITU-T 2015
K.12- Characteristics of gas discharge tubes for the protection of 2016
telecommunications installations). It shall be used to protect equipment 2017
from transient voltages. 2018
Even if a GDT operates during the occurrence of transient voltages, it is not 2019
hazardous according to 5.2.2.4, Electrical energy source ES1 and ES2 2020
limits of Single pulses. 2021
NOTE These single pulses do not include transients 2022
Because a transient does not cause a hazardous electric shock , the 2023
separation element does not need to be a reinforced safeguard nor a 2024
basic safeguard in the meaning of IEC 62368-1. 2025
If suitable components are connected in-series to the SPD (such as a VDR, 2026
etc.), a follow current will not occur, and there will be no harmful effect. 2027
5.5.8 Insulation between the mains and an external circuit consisting of a coaxial 2028
cable 2029
Source: IEC 60065:2014, 10.2 and IEC 60950-1:2005, 1.5.6. 2030
Rationale: The additional conditioning of G.10.2 comes from IEC 60950-1:2005, 1.5.6 2031
Capacitors bridging insulation 2032
Met opmerkingen [RJ2]: See Brussels minutes 6.2.11
Met opmerkingen [JR3]: See Shanghai minutes item 6.1.4
– 62 – IEC TR 62368-2:2019 © IEC 2019
5.6 Protective conductor 2033
See Figure 23 in this document for an overview of protective earthing and 2034
protective bonding conductors. 2035
2036
Figure 23 – Overview of protective conductors 2037
5.6.1 General 2038
Source: IEC 60364-5-54, IEC 61140, IEC 60950-1 2039
Purpose: The protective earthing should have no excessive resistance, sufficient 2040
current-carrying capacity and not be interrupted in all circumstances. 2041
5.6.2.2 Colour of insulation 2042
Source: IEC 604461 2043
Purpose: For clear identification of the earth connection. 2044
An earthing braid is a conductive material, usually copper, made up of 2045
three or more interlaced strands, typically in a diagonally overlapping 2046
pattern. 2047
It should be noted that IEC 60227-1:2007 has specific requirements for the 2048
use of the colour combination as follows: 2049
2050
2051
___________
1 This publication was withdrawn.
IEC TR 62368-2:2019 © IEC 2019 – 63 –
5.6.3 Requirements for protective earthing conductors 2052
Source: IEC 60950-1 2053
Purpose: The reinforced protective conductor has to be robust enough so that the 2054
interruption of the protective conductor is prevented in any case 2055
(interruption is not to be assumed). 2056
Rationale: These requirements have been successfully used for products in the scope 2057
of this document for many years. 2058
Where a conduit is used, if a cord or conductor exits the conduit and is not 2059
protected, then the values of Table 30 cannot be used for the conductor 2060
that exits the conduit. 2061
For pluggable equipment type B and permanently connected 2062
equipment, an earthing connection is always expected to be present. The 2063
earthing conductor can therefore be considered as a reinforced 2064
safeguard. 2065
5.6.4 Requirements for protective bonding conductors 2066
Source: IEC 60950-1 2067
Purpose: To demonstrate the fault current capability and the capability of the 2068
termination. 2069
Rationale: These requirements and tests have been successfully used for products in 2070
the scope of this document for many years (see Figure 3 in this document). 2071
5.6.5 Terminals for protective conductors 2072
5.6.5.1 Requirements 2073
Source: IEC 60998-1, IEC 60999-1, IEC 60999-2, IEC 60950-1 2074
Purpose: To demonstrate the fault current capability and the capability of the 2075
termination. 2076
Rationale: Conductor terminations according to Table 3 2 have served as reliable 2077
connection means for products complying with IEC 60950-1 for many years. 2078
The value of 25 A is chosen to cover the minimum protective current rating 2079
in all countries of the world. 2080
5.6.6.2 Test method 2081
Source: IEC 60950-1 2082
Rationale: This method has been successfully used for products in the scope of this 2083
document for many years. 2084
5.6.7 Reliable connection of a protective earthing conductor 2085
Source: IEC 60309 (plugs and socket outlets for industrial purpose) 2086
Purpose: To describe reliable earthing as provided by permanently connected 2087
equipment, pluggable equipment type B, and pluggable equipment 2088
type A. 2089
Rationale: Permanently connected equipment is considered to provide a reliable 2090
earth connection because it is wired by an electrician. 2091
Pluggable equipment type B is considered to provide a reliable earth 2092
connection because IEC 60309 type plugs are more reliable and earth is 2093
always present as it is wired by an electrician. 2094
For stationary pluggable equipment type A where a skilled person 2095
verifies the proper connection of the earth conductor . 2096
– 64 – IEC TR 62368-2:2019 © IEC 2019
5.7 Prospective touch voltage, touch current and protective conductor current 2097
Source: IEC 60990 2098
5.7.3 Equipment set-up, supply connections and earth connections 2099
Rationale: Equipment that is designed for multiple connections to the mains, where 2100
more than one connection is required, shall be subjected to either of the 2101
tests below: 2102
– have each connection tested individually while the other connections 2103
are disconnected, 2104
– have each connection tested while the other connections are 2105
connected, with the protective earthing conductors connected 2106
together. 2107
For simultaneous multiple connections, the requirement in the document is 2108
that each connection shall be tested while the other connections are 2109
connected, with the protective earthing conductors connected together. 2110
If the touch current exceeds the limit in 5.2.2.2, the touch current shall 2111
be measured individually. 2112
This means that if the total touch current with all connections tested 2113
together does not exceed the limit, the equipment complies with the 2114
requirement, if not, and each of the individual conductor touch currents 2115
don’t exceed the limit, the equipment also compl ies with the requirement. 2116
5.7.5 Earthed accessible conductive parts 2117
Rationale: Figure 24 in this document is an example of a typical test configuration for 2118
touch current from single phase equipment on star TN or TT systems. 2119
Other distribution systems can be found in IEC 60990. 2120
2121
Figure 24 – Example of a typical touch current measuring network 2122
5.7.6 Requirements when touch current exceeds ES2 limits 2123
Source: IEC 61140:2001, IEC 60950-1 2124
Rationale: The 5 % value has been used in IEC 60950-1 for a long time and is 2125
considered acceptable. The 5 % value is also the maximum allowed 2126
protective conductor current (7.5.2.2 of IEC 61140:2001). 2127
IEC TR 62368-2:2019 © IEC 2019 – 65 –
In the case that the protective conductor current exceeds 10 mA, 2128
IEC 61140 requires a reinforced protective earthing conductor with a 2129
conductor size of 10 mm2 copper or 16 mm2 aluminium or a second 2130
terminal for a second protective earthing conductor . This paragraph of 2131
IEC 62368-1 takes that into account by requiring a reinforced or double 2132
protective earthing conductor as per 5.6.3. 2133
IEC 61140:2001, 7.5.2.2 requires information about the value of the 2134
protective conductor current to be in the documentation and in the 2135
instruction manual, to facilitate the determination that the equipment with 2136
the high protective conductor current is compatible with the residual 2137
current device which may be in the building installation. 2138
The manufacturer shall indicate the value of the protective conductor 2139
current in the installation instructions if the current exceeds 10 mA, this to 2140
be in line with the requirements of IEC 61140:2001, 7.6.3.5. 2141
5.7.7 Prospective touch voltage and touch current associated with external circuits 2142
5.7.7.1 Touch current from coaxial cables 2143
Source: IEC 60728-11 2144
Purpose: To avoid having an unearthed screen of a coaxial network within a building. 2145
Rationale: An earthed screen of a coaxial network is reducing the risk to get an 2146
electric shock. 2147
Coaxial external interfaces very often are connected to antennas to receive 2148
TV and sound signals. Antennas installed outside the buildings are 2149
exposed to external atmospheric discharges ( for example, indirect 2150
lightning). To protect the antenna system and the equipment connecte d to 2151
such antennas, a path to earth needs to be provided via the screen of the 2152
coaxial network. 2153
Each piece of mains-powered equipment delivers touch current to a 2154
coaxial external circuit via the stray capacitance and the capacitor (if 2155
provided) between mains and coaxial interface. This touch current is 2156
limited by the requirement for each individual equipment to comply with the 2157
touch current requirements (safe value) to be measured according 2158
IEC 60990. Within a building, much individual equipment ( for example, TV’s 2159
receivers) may be connected to a coaxial network ( for example, cable 2160
distribution system). In this case , the touch current from each individual 2161
equipment sums up in the shield of the coaxial cable. With an earthed 2162
shield of a coaxial cable, the touch current has a path back to the source 2163
and the shield of the coaxial cable remains safe to touch. 2164
5.7.7.2 Prospective touch voltage and touch current associated with paired 2165
conductor cables 2166
Source: IEC 62151 2167
Purpose: To avoid excessive prospective touch voltage and excessive currents 2168
from equipment into communication networks ( for example, 2169
telecommunication networks). 2170
Rationale: All touch current measurements according to IEC 60990 measure the 2171
current from the mains to accessible parts. ES1 circuits are permitted to 2172
be accessible by an ordinary person and therefore it is included in the 2173
measurement according to IEC 60990. Circuits of class ES2 are not 2174
accessible and therefore these classes of circuits are not covered in the 2175
measurements according to IEC 60990. 2176
– 66 – IEC TR 62368-2:2019 © IEC 2019
Because ES2 circuits may be accessible to instructed persons and may 2177
become accessible during a single fault to an ordinary person, the touch 2178
current to external circuit has to be limited, to protect people working on 2179
networks or on other equipment, which are connected to the external 2180
circuit via a network. 2181
An example for an external interface ID 1 of Table 13 is the connection to a 2182
telecommunication network. It is common for service personal of 2183
telecommunication networks and telecommunication equi pment to make 2184
servicing under live conditions. Therefore, the telecommunication networks 2185
are operating with a voltage not exceeding energy class ES2. 2186
The rationale to limit the touch current value to 0,25 mA (lower than ES2) 2187
has a practical background. Telecommunication equipment very often have 2188
more than one external circuit ID 1 of Table 13 (for example, connection 2189
to a telecommunication network). In such configurations a summation of the 2190
touch current may occur (see 5.7.7). With the limitation to 0,25 mA per 2191
each individual external circuit up to 20 external circuits could be 2192
connected together without any additional requirement. In 5.7.7 this value 2193
of 0,25 mA is assumed to be the touch current from a network to the 2194
equipment. 2195
5.7.8 Summation of touch currents from external circuits 2196
Source: IEC 60950-1 2197
Purpose: To avoid excessive touch currents when several external circuits are 2198
connected. 2199
Rationale: When limiting the touch current value to each individual external circuit 2200
(as required in 5.7.6.2), more circuits can be connected together before 2201
reaching the touch current limit. This allows better utilization of resources. 2202
Detailed information about touch currents from external circuits is given 2203
in Annex W of IEC 60950-1:2005. 2204
a) Touch current from external circuits 2205
There are two quite different mechanisms that determine the current 2206
through a human body that touches an external circuit, depending on 2207
whether or not the circuit is earthed. This distinction between earthed and 2208
unearthed (floating) circuits is not the same as between class I equipment 2209
and class II equipment. Floating circuits can exist in class I equipment and 2210
earthed circuits in class II equipment. Floating circuits are commonly, but 2211
not exclusively, used in telecommunication equipment and earthed circuits 2212
in data processing equipment, also not exclusively. 2213
In order to consider the worst case, it will be assumed in this annex that 2214
telecommunication networks are floating and that the AC mains supply and 2215
human bodies (skilled persons, instructed persons or ordinary 2216
persons) are earthed. It should be noted that a skilled person and an 2217
instructed person can touch some parts that are not accessible by an 2218
ordinary person. An "earthed" circuit means that the circuit is either 2219
directly earthed or in some way referenced to earth so that its potential with 2220
respect to earth is fixed. 2221
a.1) Floating circuits 2222
If the circuit is not earthed, the current ( Ic) through the human body is 2223
"leakage" through stray or added capacitance ( C) across the insulation in 2224
the mains transformer (see Figure 25 in this document). 2225
IEC TR 62368-2:2019 © IEC 2019 – 67 –
2226
Figure 25 – Touch current from a floating circuit 2227
This current comes from a relatively high voltage, high impedance source, 2228
and its value is largely unaffected by the operating voltage on the external 2229
circuit. In this document, the body current (Ic) is limited by applying a test 2230
using the measuring instrument in Annex D of IEC 60950-1:2005, which 2231
roughly simulates a human body. 2232
a.2) Earthed circuits 2233
If the external circuit is earthed, the current through the human body ( Iv) 2234
is due to the operating voltage (V) of the circuit, which is a source of low 2235
impedance compared with the body (see Figure 26 in this document). Any 2236
leakage current from the mains transformer (see a.1), will be conducted to 2237
earth and will not pass through the body. 2238
2239
Figure 26 – Touch current from an earthed circuit 2240
In this document, the body current (Iv) is limited by specifying maximum 2241
voltage values for the accessible circuit, which shall be an ES1 circuit or 2242
(with restricted accessibility) an ES2 circuit. 2243
b) Interconnection of several equipments 2244
It is a characteristic of information technology equipment, in particular in 2245
telecommunication applications, that many equipments may be connected 2246
to a single central equipment in a "star" topology. An example is tele phone 2247
extensions or data terminals connected to a PABX, which may have tens or 2248
hundreds of ports. This example is used in the following description (see 2249
Figure 27 in this document). 2250
– 68 – IEC TR 62368-2:2019 © IEC 2019
2251
Figure 27 – Summation of touch currents in a PABX 2252
Each terminal equipment can deliver current to a human body touching the 2253
interconnecting circuit ( I1, I2, etc.), added to any current coming from the 2254
PABX port circuitry. If several circuits are connected to a common point, 2255
their individual touch currents will add together, and this represents a 2256
possible risk to an earthed human body that touches the interconnection 2257
circuit. 2258
Various ways of avoiding this risk are considered in the following 2259
subclauses. 2260
b.1) Isolation 2261
Isolate all interconnection circuits from each other and from earth, and limit 2262
I1, I2, etc., as described in a.1. This implies either the use in the PABX of a 2263
separate power supply for each port, or the provision of an individual line 2264
(signal) transformer for each port. Such solutions may not be cost effective. 2265
b.2) Common return, isolated from earth 2266
Connect all interconnection circuits to a common return point that is 2267
isolated from earth. (Such connections to a common point may in any case 2268
be necessary for functional reasons.) In this case the total current from all 2269
interconnection circuits will pass through an earthed human body that 2270
touches either wire of any interconnection circuit. This current can only be 2271
limited by controlling the values I1, I2, .. In. In relation to the number of 2272
ports on the PABX. However, the value of the total current will probably be 2273
less than I1 + I2 +... + In due to harmonic and other effects. 2274
b.3) Common return, connected to protective earth 2275
Connect all interconnection circuits to a common return point and connect 2276
that point to protective earthing. The situation described in a.2) applies 2277
regardless of the number of ports. Since safety depends on th e presence of 2278
the earth connection, it may be necessary to use high -integrity earthing 2279
arrangements, depending on the maximum value of the total current that 2280
could flow. 2281
IEC TR 62368-2:2019 © IEC 2019 – 69 –
5.8 Backfeed safeguard in battery backed up supplies 2282
Source: IEC 62040-1:2017, IEC 62368-1, UL 1778 5 th edition 2283
Purpose: To establish requirements for certain battery backed up power supply 2284
systems that are an integral part of the equipment and that have the 2285
capability to backfeed to the mains of the equipment during stored energy 2286
mode. Examples include CATV network distribution supplies and any other 2287
integral supply commonly evaluated under this document with a battery 2288
backed option. 2289
Rationale: Principles of backfeed protection 2290
Battery backed up supplies store and generate hazardous energy . These 2291
energies may be present at the input terminals of the unit. 2292
A backfeed safeguard is intended to prevent ordinary persons, 2293
instructed persons or skilled persons from unforeseeable or 2294
unnecessary exposure to such hazards. 2295
A mechanical backfeed safeguard should meet a minimum air gap 2296
requirement. If not, the mechanical device (contacts) may be forced closed, 2297
and this will not be counted as a fault. The backfeed safeguard operates 2298
with any and all semiconductor devices in any single phase of the mains 2299
power path failed. 2300
A backfeed safeguard works under any normal operating condition . This 2301
should include any output load or input source condition deemed normal by 2302
the manufacturer; however, it is common practice to only test at full - and 2303
no-load conditions, unless analysis of the circuitry proves other conditions 2304
would be less favourable. The circuitry that controls the backfeed 2305
safeguard is intended to be single-fault tolerant. 2306
A backfeed safeguard can accomplish this by disconnecting the mains 2307
supply wiring from the internal energy source, by disabling the inverter and 2308
removing the hazardous source(s) of energy, reducing the source to a safe 2309
level, or by placing a suitable safeguard between the ordinary person, 2310
instructed person or skilled person and the hazardous energy. ES1 is 2311
defined in the body of this document. The method of measurement is as 2312
follows: 2313
– For pluggable equipment, it is determined by opening all phases, 2314
neutral and ground. 2315
– For permanently connected equipment, the neutral and ground are not 2316
removed during the backfeed tests. 2317
Measurements are taken at the unit input connections across the phases, 2318
from phase to neutral and phase and neutral to ground, using the body 2319
impedance model as the measurement device. 2320
Air gap requirements for mechanical disconnect: 2321
An air gap is only required when the backfeed safeguard is mechanical in 2322
nature. The air gap is defined as the clearance distance. There are several 2323
elements to consider when determining the clearance requirement: 2324
– Under normal operation, the space between poles of phases must meet 2325
the requirements for basic insulation (see 5.4.2). 2326
– If the unit is operating on inverter, the source is considered to be a 2327
secondary supply, which is transient free (see 5.4.2). 2328
For a unit with floating outputs, opening all phases and the neutral using 2329
the required clearance for basic insulation is considered acceptable. If 2330
the output is grounded to the chassis , reinforced insulation or equivalent 2331
is required. 2332
– 70 – IEC TR 62368-2:2019 © IEC 2019
Fault testing 2333
All backfeed safeguard control circuits are subjected to failure analysis 2334
and testing. 2335
Relays 2336
Relays in the mains path that are required to open for mechanical 2337
protection should be normally open when not energized. 2338
If the relay does not meet the required clearances, the shorting of either 2339
pole/contact may be considered as a single fault to simulate the welding of 2340
the contacts. The failure of a single relay contact may be sensed and the 2341
inverter disabled to prevent feedback. 2342
A relay used for mechanical protection shall be horsepower-rated or pass a 2343
50-cycle endurance test at 600 % of the normal switching current. 2344
Electronic protection 2345
Electronic protection for a backfeed safeguard is acceptable if the 2346
operation of the electronic protection device is sensed and the inverter is 2347
disabled if a fault is found. This is the same requirement as for a relay 2348
having less than the required air gap or clearance or is not relied upon 2349
entirely for mechanical protection. 2350
Mechanical protection 2351
Mechanical protection for a backfeed safeguard is acceptable if it prevents 2352
the user from accessing greater than ES1 and cannot be readily defeated 2353
without the use of tool. The voltage rating of the mechanical protection 2354
should be no less than the maximum out -of-phase voltage. 2355
Control circuitry 2356
The failure, open- or short-circuit, of any component of the backfeed 2357
safeguard circuitry may be analyzed to evaluate the effects on the proper 2358
operation of the backfeed safeguard. Testing may be done on all 2359
components where analysis of the results is arguable. 2360
Components, such as resistors and inductors, are considered to fail open-2361
circuit only. In general, capacitors may fail open or shorted. Solid -state 2362
devices typically fail short and then open. 2363
Microprocessor controls are considered to be acceptable if the circuit 2364
operates safely with any single control line open or shorted to control logic 2365
ground, or shorted to Vcc where such fault is likely to occur . Failure of the 2366
microprocessor can also be simulated by opening the Vcc pin or shorting 2367
the Vcc pin to ground. 2368
If the control circuitry is fully redundant, (for example, N + 1), failure 2369
analysis of individual components is not required if the failure of one circuit 2370
results in a fail-safe mode of operation. 2371
_____________ 2372
6 Electrically-caused fire 2373
Rationale: Electrically-caused fire is due to conversion of electrical energy to thermal 2374
energy, where the thermal energy heats a fuel material to pyrolyze the solid 2375
into a flammable gas in the presence of oxygen. The resulting mixture is 2376
heated further to its ignition temperature which is followed by c ombustion of 2377
that fuel material. The resulting combustion, if exothermic or with additional 2378
thermal energy converted from the electrical source, can be sustained and 2379
subsequently ignite adjacent fuel materials that result in the spread of fire. 2380
IEC TR 62368-2:2019 © IEC 2019 – 71 –
The three-block model (see 0.7.2, Figure 6) for electrically (internally) 2381
caused fire addresses the separation of a potential ignition sources from 2382
combustible materials. In addition, it can also represent an ignited fuel and 2383
the safeguards interposed between ignited fuels and adjacent fuels or to 2384
fuels located outside the equipment. 2385
6.2 Classification of power sources (PS) and potential ignition sources (PIS) 2386
Rationale: The first step in the application of this clause is to determine which energy 2387
sources contain potential ignition sources requiring a safeguard. The 2388
power available to each circuit can first be evaluated to determine the 2389
energy available to a circuit. Then each point or component within a circuit 2390
can be tested to determine the power that would be avail able to a fault at 2391
that component. With this information each part of the component energy 2392
sources within the product can be classified as either a specific ignition 2393
source or a component within a power source. 2394
Throughout the clause, the term “reduce the likelihood of ignition” is used 2395
in place of the terms “prevent” or “eliminate”. 2396
6.2.2 Power source circuit classifications 2397
Source: IEC 60950-1, IEC 60065 2398
Rationale: These power source classifications begin with the lowest available energy 2399
necessary to initiate an electronic fire (PS1) and include an intermediate 2400
level (PS2) where ignition is possible but the spread of fire can be localized 2401
with effective material control or isolation safeguards. The highest energy 2402
level (PS3), assumes both ignition and a po tential spread of fire beyond the 2403
ignition source. Criteria for safeguards will vary based on the type of 2404
power source that is providing power to the circuit. 2405
This power measurement and source classification are similar to LPS test 2406
requirements from IEC 60950-1 but are applied independently and the 2407
criteria limited to available power as opposed to in combination of criteria 2408
required in IEC 60950-1. 2409
All circuits and devices connected or intended to be connected as a load to 2410
each measured power source are classified as being part of that power 2411
source. This test method determines the maximum power available from a 2412
power source to any circuit connected to that power source. 2413
The identification of test points for determination of power source is at the 2414
discretion of the manufacturer. The most obvious are outputs of internal 2415
power supply circuits, connectors, ports and board to board connections. 2416
However, these measurements can be made anywhere within a circuit. 2417
When evaluating equipment (peripherals) connected v ia cables to an 2418
equipment port or via cable, the impedance of any connecting cable may be 2419
taken into account in the determination of the PS classification of a 2420
connected peripheral. Therefore, it is acceptable to make the measurement 2421
at the supply connector or after the cable on the accessory side. 2422
The location of the wattmeter is critical , as the total power available from 2423
the power source (not the power available to the fault) is measured during 2424
each fault condition. As some fault currents may be limited by a protective 2425
device, the time and current breaking characteristics of the protective 2426
device used is considered where it has an effect on the value measured. 2427
This test method assumes a single fault in either the power source or the 2428
load circuits of the circuit being classified. It assumes both: 2429
a) a fault within the circuit being classified , and 2430
b) any fault within the power source supplying power to the circuit being 2431
classified, 2432
each condition a) or b) being applied independently. 2433
– 72 – IEC TR 62368-2:2019 © IEC 2019
The higher of the power measured is considered the PS circuit 2434
classification value. 2435
6.2.2.2 Power measurement for worst-case fault 2436
Rationale: This test method determines the maximum power available from a power 2437
source that is operating under normal operating conditions to any c ircuit 2438
connected to that power source, assuming any single fault condition within 2439
the circuit being classified. This power measurement assumes normal 2440
operating conditions are established before applying the single fault to any 2441
device or insulation in the load circuit to determine the maximum power 2442
available to a circuit during a fault. 2443
This is different for potential ignition source power measurements where 2444
the measured power available is that at the fault location. 2445
A value of 125 % was chosen to have some degree of certainty that the 2446
fuse will open after a certain amount of time. As such, the measured 2447
situation will not be a continuous situation. It was impossible to use the 2448
interruption characteristics of a fuse, since different types of interrupting 2449
devices have completely different interrupting characteristics. The value of 2450
125 % is a compromise that should cover the majority of the situations. 2451
6.2.2.3 Power measurement for worst-case power source fault 2452
Rationale: This test method determines the maximum power available to a normal load 2453
from a power source assuming any single fault within the power source. A 2454
power source fault could result in an increase in power drawn by a normal 2455
operating load circuit. 2456
6.2.2.4 PS1 2457
Source: IEC 60065, IEC 60695, IEC 60950-1 2458
Rationale: A PS1 source is considered to have too little energy to cause ignition in 2459
electronic circuits and components. 2460
The requirement is that the continuous available power be less than 15 W 2461
to achieve a very low possibility of ignition. The value of 15 W has been 2462
used as the lower threshold for ignition in electronic components in many 2463
documents, including IEC 60950-1 and IEC 60065. It has also routinely 2464
been demonstrated through limited power fault testing in electronic circuits. 2465
– In order to address the ease of measurement, it was decided to make 2466
the 15 W measurement after 3 s. The value of 3 s was chosen to permit 2467
ease of measurement. Values as short as 100 ms and as high as 5 s 2468
were also considered. Quickly establishing a 15 W limit (less than 1 s) is 2469
not practical for test purposes and not considered important for typical 2470
fuel ignition. It is recognized that it normally takes as long as 10 s for 2471
thermoplastics to ignite when impinged directly by a small flame 2472
(IEC 60695 small scale material testing methods). 2473
– In principle the measurements are to be made periodically (for example, 2474
each second) throughout the 3 s period with the expectation that after 3 2475
s, the power would “never” exceed 15 W. 2476
– Historically telecommunication circuits (Table 13, ID 1) are power limited 2477
by the building network to values less than 15 W and the circuits 2478
connected to them are considered PS1 (from IEC 60950-1). 2479
It should be noted that the statement for external circuits is not intended 2480
to cover technologies such as USB and PoE. It is meant to relate to 2481
analogue ringing signals only. 2482
IEC TR 62368-2:2019 © IEC 2019 – 73 –
6.2.2.5 PS2 2483
Source: IEC 60695-11-10, IEC 60950-1 2484
Rationale: Power Source 2 assumes a level of energy that has the possibility of 2485
ignition and subsequently requires a safeguard. Propagation of the ignition 2486
beyond the initially ignited component is limited by the low energy 2487
contribution to the fault and subsequently by safeguards to control the 2488
ignition resistance of nearby fuels. 2489
The primary requirement is to limit power available to these circ uits to no 2490
more than 100 W. This value includes both power available for normal 2491
operation and the power available for any single fault condition . 2492
– This value has been used in IEC 60950-1 for a similar purpose, where 2493
ignition of internal components is poss ible but fire enclosures are not 2494
required. 2495
– The value of 100 W is commonly used in some building or fire codes to 2496
identify where low power wiring can be used outside of a fire containing 2497
enclosure. 2498
– The value is also 2 × 50 W, which can be related to the energy of 2499
standard flaming ignition sources ( IEC 60695-11-10 test flame) on 2500
which our small-scale V-rating material flammability classes are 2501
based. It is recognized that the conversion of electrical energy to 2502
thermal energy is far less than 100 %, so this value is compatible with 2503
the safeguards prescribed for PS2 circuits, which are generally 2504
isolation and V-rated fuels. 2505
The 5 s measurement for PS2 ensures the available power limits are both 2506
limited and practical for the purposes of measurement. The value is also 2507
used in IEC 60950 series as referenced above. No short-term limits are 2508
considered necessary, as possibility of ignition is presumed for 2509
components in these power limited circuits , recognizing that it generally 2510
takes 10 s or more for thermoplastics to pyrolyze and then ignite when 2511
impinged directly by a small 50 W flame. 2512
Reliability of overcurrent devices (such as those found in IEC 60950 series) 2513
is not necessary as these circuits are used within or directly adjacent to the 2514
product (not widely distributed like IEC 60950-1 LPS circuits used for 2515
connection to building power). The reliability assessment for PS2 circuits 2516
that are intended to be distributed within the building wiring is addressed 2517
for external circuits later in this document. 2518
6.2.2.6 PS3 2519
Rationale: PS3 circuits are circuits that are not otherwise classified as PS1 or PS2 2520
circuits. No classification testing is required as these circuits can have 2521
unlimited power levels. If a circuit is not measured, it can be assumed to be 2522
PS3. 2523
6.2.3 Classification of potential ignition sources 2524
Rationale: With each power source, points and components within a circuit can be 2525
evaluated to determine if potential ignition sources are further identified. 2526
These ignition sources are classified as either an arcing PIS for arcing 2527
sources or a resistive PIS for resistance heating sources. Criteria for 2528
safeguards will vary based on the type of PIS being addressed. 2529
Ignition sources are classified on their ability to either arc or dissipate 2530
excessive heat (resistive). It is important to distinguish the type of ignition 2531
source as distances through air from arcing parts v ersus other resistive 2532
ignition sources vary due to a higher thermal loss in radiated energy as 2533
compared to conducted flame or resistive heat impinging direc tly on a 2534
combustible fuel material. 2535
– 74 – IEC TR 62368-2:2019 © IEC 2019
6.2.3.1 Arcing PIS 2536
Source: IEC 60065 2537
Rationale: Arcing PIS are considered to represent a thermal energy source that 2538
results from the conversion of electrical energy to an arc, which may 2539
impinge directly or indirectly on a fuel material. 2540
Power levels below 15 W (PS1) are considered to be too low to initiate an 2541
electrical fire in electronic circuits. This value is used in IEC 60065 (see 2542
also 6.2.1). 2543
The minimum voltage (50 V) required to initiate arcing is also from 2544
IEC 60065 and through experimentation. 2545
For low-voltages, the fault that causes arc -heating is generally a result of a 2546
loose connection such as a broken solder connection, a cold -solder 2547
connection, a weakened connector contact, an improperly crimped wire, an 2548
insufficiently tightened screw connection, etc. As air does not breakdown 2549
below 300 V RMS. (Paschen’s Law), most low voltage arc -heating occurs 2550
in direct contact with a fuel. For voltages greater than 300 V, arcing can 2551
occur through air. 2552
The measurement of voltage and current necessary to establish an arcing 2553
PIS is related the energy that is available to the fault (as opposed to 2554
energy available from a power source). The value ( Vp × Irms) specified is 2555
neither a W or VA but rather a calculated number reflecti ng a peak voltage 2556
and RMS current. It is not directly measurable. 2557
Arcing below 300 V is generally the result of a disconnection of current -2558
carrying connections rather than the mating or connection of potentially 2559
current-carrying connections. 2560
Once the basic parameters of voltage and power are met, there are three 2561
conditions for which safeguards are required: 2562
– those that can arc under normal operating conditions ; 2563
– all terminations where electrical failure resulting in heating is more 2564
likely; and 2565
– any electrical separation that can be created during a single fault 2566
condition (such as the opening of a trace). 2567
A reliable connection is a connection which is expected not to become 2568
disconnected within the lifetime of the equipment . The examples in the note 2569
give an idea as to what kinds of connections can be considered reliable. 2570
The manufacturer may declare any location to be an arcing PIS. 2571
6.2.3.2 Resistive PIS 2572
Source: IEC 60065 2573
Rationale: Resistive potential ignition sources can result from a fault that causes 2574
over-heating of any impedance in a low-resistance that does not otherwise 2575
cause an overcurrent protection to operate. This can happen in any circuit 2576
where the power to the resistive heating source is greater than 15 W (see 2577
above). A resistive PIS may ignite a part due to excessive power 2578
dissipation or ignite adjacent materials a nd components. 2579
Under single fault conditions , this clause requires that two conditions 2580
exist before determining that a part can be a resistive PIS. The first is that 2581
there is sufficient available fault energy to the component. The second is 2582
that ignition of the part or adjacent materials can occur. 2583
The requirement for a resistive PIS under normal operating conditions is 2584
not the available power but rather the power dissipation of th e part under 2585
normal operating conditions. 2586
IEC TR 62368-2:2019 © IEC 2019 – 75 –
The value of 30 s was used in IEC 60065 and has historically proven to be 2587
sufficient. The value of 100 W was used in IEC 60065 and has historically 2588
proven to be adequate. 2589
The manufacturer may declare any location to be a resistive PIS. 2590
6.3 Safeguards against fire under normal operating conditions and abnormal 2591
operating conditions 2592
Rationale: The basic safeguard under normal operating conditions and abnormal 2593
operating conditions is to reduce the likelihood of igniti on by limiting 2594
temperature of fuels. This can be done by assuring that any available 2595
electrical energy conversion to thermal energy does not raise the 2596
temperature of any part beyond its ignition temperature. 2597
2598
Figure 28 – Possible safeguards against electrically-caused fire 2599
There are several basic safeguards and supplementary safeguards against 2600
electrically-caused fire under abnormal operating conditions and single fault 2601
conditions (see Figure 28, Table 8 and Table 9 in this document). These 2602
safeguards include, but are not limited to: 2603
S1) having insufficient power to raise a fuel material to ignition temperature; 2604
S2) limiting the maximum continuous fault current; limiting the maximum duration 2605
for fault currents exceeding the maximum continuous fault current (for example, 2606
a fuse or similar automatic-disconnecting overcurrent device); 2607
S3) selecting component rating based on single fault conditions rather than 2608
normal operating conditions (prevents the component from overheating); 2609
S4) ensuring high thermal resistance of the thermal energy transfer path from the 2610
thermal energy source to the fuel material (reduces the temperature and the 2611
rate of energy transfer to the fuel material so that the fuel material cannot 2612
attain ignition temperature); or a barrier made of non-combustible material; 2613
S5) using an initial fuel material located closest to an arcing PIS or resistive PIS 2614
having a temperature rating exceeding the temperature of the source (prevents 2615
– 76 – IEC TR 62368-2:2019 © IEC 2019
fuel ignition); or a flame-retardant fuel material (prevents sustained fuel 2616
burning and spread of fire within the equipment); or a non-combustible 2617
material (for example, metal or ceramic); 2618
S6) ensuring high thermal resistance of the thermal energy transfer path from the 2619
initial fuel to more fuel material; or flame isolation of the burning initial fuel from 2620
more fuel material (prevents spread of fire within the equipment); 2621
S7) ensuring that subsequent material is either non-combustible material (for 2622
example, metal or ceramic); or is a flame-retardant material (prevents 2623
sustained fuel burning and spread of fire within the equipment); 2624
S8) use of a fire-containing enclosure (contains the fire within the equipment) or 2625
an oxygen-regulating enclosure (quenches a fire by suffocating it); 2626
S9) use of reliable electrical connections; 2627
S10) use of non-reversible components and battery connections; 2628
S11) use of mechanical protection (for example, barriers, mesh or the like) with 2629
limited openings; 2630
S12) use of clear operating instructions, instructional safeguards, cautions. 2631
Methods of protection 2632
A) Protection under normal operating conditions and abnormal 2633
operating conditions 2634
Materials and components shall not exceed their auto-ignition temperatures. 2635
B) Protection under single fault conditions 2636
There are two methods of providing protection. Either method may be applied 2637
to different circuits in the same equipment: 2638
– Prevent ignition: equipment is so designed that under abnormal operating 2639
conditions and single fault conditions no part will ignite; 2640
– Control fire spread: selection and application of components, wiring, 2641
materials and constructional measures that reduce the spread of flame and, 2642
where necessary, by the use of a fire enclosure. 2643
Thermoplastic softening values or relative thermal indices (RTI) were not 2644
considered appropriate as they do not relate specifically to ignition properties 2645
of fuel materials. 2646
Any device that operates as a safeguard during normal operation (when left in 2647
the circuit) shall be assessed for reliability. If a device is taken out of the circuit 2648
during the normal operation testing then it is not considered as being a 2649
safeguard. 2650
Abnormal operating conditions that do not result in a single fault are 2651
considered in much the same way as normal operating conditions as the 2652
condition is corrected and normal operation is presumed to be restored. 2653
However, abnormal operating conditions that result in a single fault 2654
condition are to be treated in accordance with 6.4 rather than 6.3. See 2655
Figure 29 in this document for a fire clause flow chart. 2656
IEC TR 62368-2:2019 © IEC 2019 – 77 –
Table 8 – Examples of application of various safeguards 2657
Cause Prevention/protection methods Safeguard
Start of f ire under normal operating conditions
Limit temperature of combustible material Basic
Start of fire under abnormal operating conditions and single fault conditions
Select prevent ignition or control fire spread method
Supplementary
PS1 circuit Low available power reduces the likelihood of ignition
S1
PS2 or PS3 circuit Reduce the likelihood of ignition
Use of protection devices
S1, S2, S3, S5
S2
Sufficient distance or solid barrier interposed between any combustible material and each potential ignition source
S4 (S6)
PS2 circuit Limit the available power
Sufficient distance or solid barrier interposed between any combustible material and each potential ignition source
Use flame-retardant or non-combustible material
S1, S2
S4, S6
S5
PS3 circuit Use all PS2 options and:
− use fire containing enclosures
− use flame-retardant or similar materials
S8
S7
Internal and external wiring Reliable construction
Limit of wire temperature and use of fire resistant insulation
S9
Fire caused by entry of foreign obj ects and subsequent bridging of electrical terminals in PS2 circuits and PS3 circuits
Prevent entry of foreign objects S11
Mains supply cords Reliable construction
Limit of wire temperature and use of fire resistant insulation
S9
Fire or explosion due to abnormal operating conditions of batteries
Limit charge/discharge currents
Limit short-circuit currents
Prevent use of wrong polarity
S1
S2
S10
2658
– 78 – IEC TR 62368-2:2019 © IEC 2019
2659
Figure 29 – Fire clause flow chart 2660
6.3.1 Requirements 2661
Source: IEC 60950-1, ISO 871 2662
Rationale: Spontaneous-ignition temperature as measured by ISO 871 for materials 2663
was chosen as the ignition point of fuels. The materials specific tables 2664
were deleted in favour of a simple requirement or completely referring 2665
instead to the ASTM standard for material auto-ignition temperatures. 2666
IEC TR 62368-2:2019 © IEC 2019 – 79 –
The 300 °C value for thermoplastics is approximately 10 % less than the 2667
lowest ignition temperature of materials commonly used in ICT and CE 2668
equipment. This value has also been used in IEC 60950-1. The designer is 2669
permitted to use material data sheets for materials that exceed this value 2670
but the auto-ignition specification has to be reduced by 10 % to 2671
accommodate measurement variations and uncertainty. 2672
In the context of fire, abnormal operating conditions (blocked vents, 2673
connector overload, etc.) are to be considered just as a normal operating 2674
condition unless the abnormal operating condition results in a single 2675
fault condition. 2676
As part of the compliance check, first the datasheets of the materials used 2677
have to be checked to be able to evaluate the results of the temperature 2678
rise measurements. 2679
The glow-wire test is a fire test method of applying a heat source to the 2680
sample. The test provides a way to compare a material’s tendency to resist 2681
ignition, self-extinguish flames (if ignition occurs), and to not propagate 2682
fire. Manufacturers have been using this test method to determine a 2683
plastic’s flame resistance characteristics to IEC 60950-1 for many years 2684
without field issues identified with the suitability of the test. Hence, the 2685
glow-wire test should continue to be an option to the HB rating for plastics 2686
outside of the fire enclosure or mechanical enclosures and for electrical 2687
enclosures housing PS1 circuits. This precedence has been set in 2688
IEC 60950-1 and should be included in IEC 62368-1. 2689
Table 9 – Basic safeguards against fire under normal operating conditions 2690
and abnormal operating conditions 2691
Normal operating conditions and abnormal operating conditions
The objective of this subclause is to define requirements to reduce the likelihood of ignition under normal operating conditions and abnormal operating conditions .
PS1
PS2
PS3
6.3.1
Ignition is not allowed
Tmax
90 % auto ignition temperature according to ISO 871; or
Tmax
300 ºC
Combustible materials for components and other parts outside fire enclosures (including electrical enclosures, mechanical enclosures and decorative parts), shall have a material flammability class of at least: – HB75 if the thinnest significant thickness of this material is < 3 mm, or
– HB40 if the thinnest significant thickness of this material is 3 mm, or – HBF.
NOTE Where an enclosure also serves as a fire enclosure, the requirements for fire enclosures apply.
These requirements do not apply to:
– parts with a size of less than 1 750 mm3; – supplies, consumable materials, media and recording materials; – parts that are required to have particular properties in order to perform
intended functions, such as synthetic rubber rollers and ink tubes; – gears, cams, belts, bearings and other parts that would contribute negligible
fuel to a fire, including labels, mounting feet, key caps, knobs and the like.
2692
– 80 – IEC TR 62368-2:2019 © IEC 2019
6.3.2 Compliance criteria 2693
Rationale: Steady state for temperature measurements in excess of 300 °C requires 2694
more tolerance on the rise value due to the difficulty in achieving a stable 2695
reading. However, the value in B.1.6 was considered adequate, as these 2696
values typically do not continue to rise but rather cycle . The value of 3 °C 2697
over a 15 min period was also considered for measurement of these very 2698
high temperatures but was not used in favour of harmonization with other 2699
clauses. 2700
The use of temperature-limiting safeguards under normal operating 2701
conditions and abnormal operating conditions is considered acceptable 2702
only where the safeguard or device has been deemed a reliable 2703
temperature control device. 2704
6.4 Safeguards against fire under single fault conditions 2705
6.4.1 General 2706
Source: IEC 60065, IEC 60950-1 2707
Rationale: The consideration in the prior clause is to li mit the likelihood of 2708
ignition of fuels under normal operating conditions and abnormal 2709
operating conditions with a basic safeguard. All fuels should be used 2710
below their ignition temperatures and separated from a rcing parts. 2711
The requirements in this clause are to limit the ignition or the spread of fire 2712
under single fault conditions by employing supplementary safeguards, 2713
see Table 10 in this document. There are two approaches that can be used 2714
either jointly or independently: 2715
– method 1 minimizes the possibility of ignition through the use of 2716
safeguards applied at each potential point of ignition ; 2717
– method 2 assumes the ignition of limited fuels within the product and 2718
therefore requires safeguards that limit the spread of fire beyond the 2719
initial ignition point or for higher energy, beyond the equipment 2720
enclosure. 2721
Table 10 – Supplementary safeguards against fire under single fault conditions 2722
Single fault conditions
There are two methods of provid ing protection. Either method may be applied to different circuits of the same equipment (6.4.1)
Method 1
Reduce the likelihood of
ignition
Equipment is so designed that under single fault conditions no part shall ignite.
This method can be used for any circuit in which the available steady state power to the circuit does not exceed 4 000 W.
The appropriate requirements and tests are detailed in 6.4.2 and 6.4.3.
Method 2
Control fire spread
Selection and application of supplementary safeguards for components, wiring, materials and constructional measures that reduce the spread of fire and, where necessary, by the use of a second supplementary safeguard such as a fire enclosure.
This method can be used for any type of equipment.
The appropriate requirements are detailed in 6.4.4, 6.4.5 and 6.4.6.
2723
The document’s user or product designer will select a method to apply to each 2724
circuit, (either prevent ignition method or control the spread of fire method). 2725
The selection of a method can be done for a complet e product, a part of a 2726
product or a circuit. 2727
IEC TR 62368-2:2019 © IEC 2019 – 81 –
The power level of 4 000 W was chosen to ensure that products which are 2728
connected to low power mains (less than 240 V × 16 A), common in the office 2729
place or the home, could use the ignition protection methods , and to provide a 2730
reasonable and practical separation of product types. It is recognized that this 2731
is not representative of fault currents available but is a convenient and 2732
representative separation based on equipment connected to normal office and 2733
home mains circuits where experience with potential ignition sources 2734
safeguards is more common. 2735
Limit values below 4 000 W create a problem for the AC mains of almost all 2736
equipment used in the home or office , which is not the intent. It would be much 2737
more practical to use an energy source power of 4 000 W based on mains 2738
voltage and overcurrent device rating which would effectively permit all 2739
pluggable type A equipment to use either method, and restrict very high-2740
power energy sources to use only the method to contr ol fire spread. 2741
The 4 000 W value can be tested for individual circuits; however, a note has 2742
been added to clarify which types of products are considered below without 2743
test. Calculation of the product of the mains nominal voltage and mains 2744
overcurrent device rating is not a normal engineering convention but rather the 2745
product of two numbers should not exceed 4 000 (see text below). 2746
NOTE All pluggable equipment type A are considered to be below the steady state value of 2747 4 000 W. Pluggable equipment type B and permanently connected equipment are considered 2748 to be below this steady state value if the product of nominal mains voltage and the current rating 2749 of the installation overcurrent protective device is less than 4 000. 2750
Prevent ignition method: Prescribes safeguard requirements that would 2751
prevent ignition and is predominantly based on fault testing and component 2752
selection and designs that reduce the likelihood of sustained flaming. Where a 2753
PIS is identified, additional safeguards are required to use barriers and the fire 2754
cone ‘keep out’ areas for non -flame rated materials (see Table 11 and 2755
Figure 30 in this document). 2756
The prevent ignition method has been used in IEC 60065 where the 2757
predominant product connection is to low power (< 16 A) mains circuits. The 2758
use of this method was not considered adequate enough for larger mains 2759
circuits because the size of the fire cone does not adequately address large 2760
ignition sources common in higher power circuits. 2761
This approach limits the use of prevent ignition methods to those products 2762
where the ignition sources is characterized by the fire cones and single fault 2763
conditions described in 6.4.7. 2764
– 82 – IEC TR 62368-2:2019 © IEC 2019
Table 11 – Method 1: Reduce the likelihood of ignition 2765
Method 1: Reduce the likelihood of ignition under single fault conditions
PS1
(≤ 15 W after 3) 6.4.2
No supplementary safeguards are needed for protection against PS1.
A PS1 is not considered to contain enough energy to result in materials reaching ignition temperatures.
PS2
( PS1 and
≤ 100 W after 5 s)
and
PS3
( PS2 and
≤ 4 000 W)
6.4.3
The objective of this subclause is to define the supplementary safeguards needed to reduce the likelihood of ignition under single fault conditions in PS2 circuits and PS3 circuits where the available power does not exceed 4 000 W. All identified supplementary safeguards need to be considered based on the equipment configuration.
Sustained flaming 10 s is not allowed and no surrounding parts shall have ignited.
Separation from arcing PIS and resistive PIS according to 6.4.7
– Distances have to comply with Figures 37, 38, 39a and 39b; or
– In case the distance between a PIS and combustible material is less than specified in Figures 37, 38, 39a and 39b;
• Mass of combustible material < 4 g, or
• Shielded from the PIS by a fire barrier, or
• Flammability requirements:
o V-1 class material ; VTM-1 class material or HF-1 class material , or needle flame in Clause S.2, or
o Relevant component IEC document
Using protective devices that comply with G.3.1, G.3.2, G.3.3 and G.3.4 or the relevant IEC component documents for such devices;
Using components that comply with G.5.3, G.5.4 or the relevant IEC component document;
Components associated with the mains shall comply with:
the relevant IEC component documents; and
the requirements of other clauses of IEC 62368-1
2766
2767
IEC TR 62368-2:2019 © IEC 2019 – 83 –
IEC
TR
62
36
8-2
:20
19
© IE
C 2
01
9
– 8
3 –
Figure 30 – Prevent ignition flow chart
– 84 – IEC TR 62368-2:2019 © IEC 2019
Control fire spread method: Prescribes safeguards that are related to the spread of fire from acknowledged ignition sources. This assumes very little performance testing (no single fault conditions) and the safeguards are designed to minimize the spread of flame both within th e product and beyond the fire enclosure. The safeguards described are based on power level , with higher power sources requiring more substantial safeguards (see Figure 31, Figure 32 and Table 12 in this document).
This power (4 000 W) separation is also used in the control of fire spread method to delineate safeguard criteria for fire enclosure materials (V-1 versus 5 V). IEC 60950-1 has historically used weight to define fire enclosure criteria and it was felt that the use of available power was more appropriate and generally reflective of current practice.
IEC TR 62368-2:2019 © IEC 2019 – 85 –
IEC
TR
62
36
8-2
:20
19
© IE
C 2
01
9
– 8
5 –
Figure 31 – Control fire spread summary
– 86 – IEC TR 62368-2:2019 © IEC 2019 –
86
–
IEC
TR
62
36
8-2
:20
19
© IE
C 2
01
9
Figure 32 – Control fire spread PS2
IEC TR 62368-2:2019 © IEC 2019 – 87 –
IEC
TR
62
36
8-2
:20
19
© IE
C 2
01
9
– 8
7 –
Figure 33 – Control fire spread PS3
– 88 – IEC TR 62368-2:20xx © IEC 2019
6.4.2 Reduction of the likelihood of ignition under single fault conditions in PS1 1
circuits 2
Rationale: Low available power prevents ignition – 15 W is recognized as the lower 3
limit of ignition for electronic products. The limiting of power is not 4
considered the basic safeguard but rather the characteristic of the circuit 5
being considered. This determination is made as part of the classification 6
of power sources. 7
6.4.3 Reduction of the likelihood of ignition under single fault conditions in PS2 8
circuits and PS3 circuits 9
Rationale: To identify all potential ignition sources, all circuits and components 10
within the PS2 and PS3 circuits should be evaluated for their propensity to 11
ignite. 12
The ignition source derived from either PS2 or a PS3 circuit is considered 13
equivalent. The resulting flame size and burn time is identical in all PS2 14
and PS3 circuits unless the power available is very large (for example, 15
greater than 4 000 W). 16
For very large sources (greater than 4 000 W) the safeguards described 17
for addressing potential ignition sources are not recognized as being 18
adequate and the control fire spread method is used (see 6.4.1 for 4 000 W 19
rationale). 20
6.4.3.1 Requirements 21
Source: IEC 60065, IEC 60695-2-13, IEC 60950-1 22
Rationale: Flaming of a fuel under single fault conditions is only permitted if very 23
small and quickly extinguished (for example , a fusing fuse resistor). A 24
length of time is necessary during single fault conditions to permit the 25
characteristic “spark” or short term “combustion flash” common when 26
performing single fault conditions in electronic circuits. The value of 10 s 27
is used, which has been used by IEC 60065 for many years. The energy of 28
this short-term event is considered too low to ignite other parts. This value 29
corresponds with IEC 60695-2-13 and has been used in practice by IEC TC 30
89 for glow wire ignition times. The time period is necessary to 31
accommodate the expected flash/short duration flames that often result as 32
a consequence of faults. The value of 10 s is considered to be the 33
minimum time needed for ignition of commonly used thermoplastics by 34
direct flame impingement. It is recognized that times as short as 2 s are 35
used by other documents. 36
Protection is achieved by identifying each PIS and then limiting the 37
temperature of parts below auto-ignition temperatures during single fault 38
conditions, minimizing the amount of flammable material near a PIS, 39
separating combustible materials from PIS by barriers, and by using 40
reliable protection devices to limit temperature of combustible parts. 41
Single fault testing, while not statistically significant, has been common 42
practice in both IEC 60065 and IEC 60950-1. 43
Temperatures limiting ignition are considered to be the material self -44
ignition points or flash temperatures for flammable liquids and vapours (this 45
value should include a 10 % margin to take into account ambient, 46
laboratory and equipment operat ing conditions). The spread to surrounding 47
parts during and after the fault is also checked. 48
IEC TR 62368-2:20xx © IEC 2019 – 89 –
Providing sufficient distance or solid barrier between any combustible 49
material and a potential ignition source should minimize the potential for 50
the spread of fire beyond the fuels directly in contact with the potential 51
ignition source. The fire cone distances developed for IEC 60065 are 52
used and considered adequate. We prescribed the use of the cone 53
because it is more reliable than single fault testing. Single fault testing is 54
not completely representative; therefore, some material and construction 55
requirements are necessary (fuel control area or keep out area). 56
Use of reliable protection devices – This includes reliability requirements 57
for the devices that are used to prevent ignition. This permits only the use 58
of devices that have reliability requirements included in Annex G. 59
Components that comply with their relevant IEC component documents 60
standards are also considered to comply given these documents standards 61
also have ignition protection requirements. The components included are 62
those that are almost always part of a potential ignition source as they 63
are mains connected. 64
Opening of a conductor: In general, opening of a conductor is not permitted 65
during single fault conditions as it is not considered reliable protection 66
device for limiting ignition. However for resistive PIS, it may be suitable 67
provided the printed wiring board is adequately flame retardant and the 68
opening does not create an arcing PIS. The V-1 printed circuit board is 69
considered adequate to quench low voltage events and will not propagate 70
the flame. It is not sufficient when the opening creates an arcing PIS 71
(< 50 V). 72
As a consequence of the test, any peeling of conductor during these tests 73
shall not result in or create other hazards associated with the movement of 74
conductive traces during or after the test provided they do so predictably. 75
During a single fault the peeling could bridge a basic safeguard but should 76
not result in the failure of a supplementary safeguard or reinforced 77
safeguard. 78
6.4.3.2 Test method 79
Source: IEC 60065, IEC 60127 80
Rationale: The available power and the classification criteria for resistive and arcing 81
potential ignition sources should be used to determine which 82
components to fault. 83
If the applied single fault condition causes another device or subsequent 84
fault, then the consequential failure is proven reliable by repeating the 85
single fault condition two more times (total of three times). This is a 86
method used historically in IEC 60065. 87
Steady state determination for single fault conditions is related to 88
temperature rise and the requirement is the same as the steady state 89
requirements of Annex B, even though material ignition temperatures 90
( 300 °C) are much higher than required temperatures of other clauses 91
(~25 °C – 100 °C). Shorter time periods (such as 15 min) were considered 92
but dropped in favour of harmonization of other parts. The term steady 93
state should take into account temperatures experienced by a material 94
throughout the test. 95
Maximum attained temperature for surrounding material of heat source 96
should be considered if further temperature increase is observed after 97
interruption of the current. 98
Limit by fusing: The reliability of protection devices is ensured where they 99
act to limit temperatures and component failures. The criteria used by the 100
component document applying to each are considered adequate provided 101
the parts are used as intended. The requirements included assume an 102
IEC 60127 type fuse as the most common device. 103
Met opmerkingen [RJ4]: See Raleigh minutes item 7.1.2
– 90 – IEC TR 62368-2:20xx © IEC 2019
The test methodology is established to ensure that available energy 104
through the fuse link based on its current hold and interrupt conditions the 105
breaking time characteristics of specified in IEC 60127. IEC 60127 permits 106
2,1 times the breaking current rating for 1 min. 107
In order to determine the impact of a fuse on the results of a single fault 108
condition, if a fuse operates, it is replaced with a short circuit and the test 109
repeated. There are three possible conditions when comparing the actual 110
fault current through the fuse to the pre -arcing current and time data 111
sheets provided by the fuse manufacturer. 112
– Where the measured current is always below the fuse manufacturer's 113
pre-arcing characteristics (measured current is less than 2,1 times the 114
fuse rating), the fuse cannot be relied upon as a safeguard and the test 115
is continued with the fuse short circuited until steady state where the 116
maximum temperature is measured. 117
– Where the measured current quickly exceeds the fuse p re-arcing 118
characteristics (measured current is well above 2,1 times the rating 119
current of the fuse) then the test is repeated with the open circuit in 120
place of the fuse (assumes fuse will open quickly and be an open circuit ) 121
and then the maximum temperature recorded. 122
– Where the measured current does not initially exceed the fuse pre -123
arcing characteristics, but does at some time after introduction of the 124
fault. The test is repeated with the short circuit in place and the 125
temperature measured at the time where measured current exceeds the 126
fuse pre-arcing characteristics. It is assumed the measured current 127
through the short circuit can be graphed and compared with the fuse 128
manufacturer’s pre-arcing curves provided on the fuse datasheet to 129
determine the test time. 130
6.4.4 Control of fire spread in PS1 circuits 131
Rationale: Low available power reduces the likelihood for ignition – 15 W is 132
recognized as the lower limit of ignition for electronic circuits. This lower 133
power limit is considered as a circuit characteristic o f the circuit, not a 134
basic safeguard. 135
IEC TR 62368-2:20xx © IEC 2019 – 91 –
Table 12 – Method 2: Control fire spread 136
Method 2: Control fire spread
PS1
(≤ 15 W) 6.4.4
No supplementary safeguards are needed for protection against PS1.
A PS1 is not considered to contain enough energy to result in materials reaching ignition temperatures.
PS2
(≤ 100 W after 5 s) 6.4.5
The objective of this subclause is to describe the supplementary safeguards needed to reduce the likelihood of fire spread from a PIS in PS2 circuits to nearby combustible materials.
The limiting of power available to PS2 circuits is the basic safeguard used to minimize the available energy of an ignition source.
A supplementary safeguard is required to control the spread of fire from any possible PIS to other parts of the equipment
For conductors and devices with a PIS the following apply:
– Printed boards shall be at least V-1 class material
– Wire insulation shall comply with IEC 60332 series or IEC 60695-11-21
Battery cells and battery packs shall comply with Annex M.
All other components:
– Mounted on V-1 class material , or
– Materials V-2 class material , VTM-2 class material , or HF-2 class material, or
– Mass of combustible material < 4 g, provided that when the part is ignited the fire does no t spread to another part, or
– Separated from PIS according to 6.4.7,
Distances have to comply with Figures 37; 38; 39 and 40, or
In case distances do not comply with Figures 37; 38; 39 and 40
– Mass of combustible material < 4 g, or
– Shielded from the PIS by a fire barrier, or
– Flammability requirements: V-1 class material ; VTM-1 class material or HF-1 class material , or comply with the needle flame test of IEC 60695-11-5 as described in Clause S.2; or
– Comply with IEC component document flammability requirements, or comply with G.5.3 and G.5.4
– Insulation materials used in transforme rs, bobbins, V-1 class material
– In a sealed enclosure ≤ 0,06 m3 made of non-combustible material and having no ventilation openings
The following shall be separated from a PIS according to 6.4.7 or shall not ignite due to fault conditional testing
– Supplies, consumables, media and recording materials
– Parts which are required to have particular properties in order to perform intended functions, such as synthetic rubber rollers and ink tubes
137
– 92 – IEC TR 62368-2:20xx © IEC 2019
138
Method 2: Control fire spread
PS3
( PS2)
The objective of this subclause is to describe the supplementary safeguards needed to reduce the likelihood of fire spread from a PIS in PS3 circuits to nearby combustible materials.
6.4.6
Fire spread in PS3 circuit shall be controlled by;
– the use of a fire enclosure as specified in 6.4.8. and
– applying all requirements for PS2 circuits as specified in 6.4.5
Devices subject to arcing or changing contact resistance (for example, pluggable connectors) shall comply with one of the following :
– Materials V-1 class material ; or
– Comply with IEC component document flammability requirements; or
– Mounted on V-1 class material and volume ≤ 1 750 mm 3
Exemptions:
– Wire and tubing insulation complying with IEC 60332 series or IEC 60695-11-21
– Components, including connectors complying wi th 6.4.8.2.2 and that fill an opening in a fire enclosure
– Plugs and connectors forming a part of a power supply cord or complying with 6.5, G. 4.1 and G.7
– Transformers complying with G .5.3
– Motors complying with G.5.4
6.4.6
For PS2 or a PS3 circuit
within a fire en-closure
See all requirements for PS2 (6.4.5)
6.4.6
For a PS1 circuit
within a fire
enclosure
Combustible materials:
Needle flame test in Clause S.1 or V-2 class material or VTM-2 class material or HF-2 class material
Exemptions:
– Parts with a size less than 1 750 mm3
– Supplies, consumable materials , media and recording materials
– Parts that are required to have particular properties in order to perform intended functions such as synthet ic rubber rollers and ink tubes
– Gears, cams, belts, bearings and other small parts that wo uld contribute negligible fuel to a fire, including, labels, mounting fee t, key caps, knobs and the like
– Tubing for air or any fluid systems, containers for powders or liquids and foamed plastic parts, provided that they are of HB75 class material if the thinnest significant thickness of the material is < 3 mm, or HB40 class material if the thinnest significant thickness of the material is ≥ 3 mm, or HBF class foamed material
139
6.4.5 Control of fire spread in PS2 circuits 140
Source: IEC 60950-1 141
Rationale: In principle, limiting the available power to the circuit (100 W) in PS2 142
circuits and control of adjacent fuel materials will reduce the spread of fire, 143
assuming that ignition of components can occur. This power level limit 144
minimizes the size of the ignition source and its impingement on adjacent 145
fuels that are in the PS2 circuits. 146
IEC TR 62368-2:20xx © IEC 2019 – 93 –
The purpose of this clause is to establish control of fuels in or near circuits 147
that have the possibility of ignition. As no fault testing is done for PS2 148
circuits, it is assumed that a fire ignition can occur anywhere within the 149
circuits. These safeguards are to be based on component material 150
flammability characteristics that keep the initial ignition source from 151
spreading to surrounding internal materials. 152
This clause assumes only construction safeguards in a manner consistent 153
with the historically effective requirements of IEC 60950-1. 154
Only fuels that would contribute significant fuel to a fire are considered. 155
Acceptance of limited power sources in Annex Q .1 to be classified as PS2 156
has been added to allow continued use of the long existing practice in 157
IEC 60950-1. 158
6.4.5.2 Requirements 159
Source: IEC 60065, IEC 60950-1 160
Rationale: Requirements around conductors and devices subject to arcing parts and 161
resistive heating have the most onerous requirements for sustained ignition 162
and protection of wiring and wiring boards. 163
– Mounting on a flame-retardant material to limit fire growth. V-1 164
mounting materials are considered important as they limit fuel to reduce 165
sustained flaming and also would not contribute to large fires or pool 166
fire. The spread of fire from ignited small parts can be managed by the 167
larger printed wiring board. This provision is made to allow the use of a 168
longstanding IEC 60950-1 provision for small devices mounted directly 169
on boards. The value 1 750 mm3 has been used in practice in 170
IEC 60065. 171
– Use of flame retardant wiring is identical to the internal and external 172
wiring requirements of Clause 6. 173
– Accepting existing component requirements for devices that have their 174
own requirements (IEC or annexes of this document) are considered 175
adequate. 176
– Sufficient distance or solid flame-resistant barrier between any 177
combustible material and potential ignition sources. (KEEP OUT 178
ZONES or RESTRICTED AREA). 179
All other components (those that are not directly associated with arcing or 180
resistive heating components) have a reduced set of safeguards when 181
compared to those parts more likely to ignite. Those safeguards include 182
any of the following: 183
– For parts not directly subject to arcing or resistive heating, V-2 ratings 184
are considered adequate. This is also a historical requirement of 185
IEC 60950-1 for parts used in limited power circuits. Sustained ignition 186
of V-2 class materials is similar to that of V-1 class materials in the 187
small-scale testing. The use of VTM-2 or HF-2 class materials were 188
also considered adequate. 189
– Limiting the combustible fuel mass within the area around PS2 circuit 190
devices. The limit of 4 g is brought from the small parts definition used 191
with PIS requirements of this clause and which were originally used in 192
IEC 60065. 193
– As an alternative, components and circuits can be separated from fuels 194
per the requirements of the fire cone described for isolation of fuels 195
from potential ignition sources. 196
– Enclosing parts in small oxygen limiting, flame proof, housing. The 197
0,06 m2 value has been in practice in IEC 60950-1 and small enough to 198
mitigate fire growth from a low power source. 199
– 94 – IEC TR 62368-2:20xx © IEC 2019
The exceptions included are based on common constructions of material 200
that do not routinely have flame retardants or that cannot contain flame 201
retardants due to functional reasons. They are either isolated from any PIS 202
or through single fault condition testing demonstrate that they will simply 203
not ignite in their application. 204
Supplies are quantities of materials such as paper, ink, toner, staples etc ., 205
and that are consumed by the equipment and replaced by the user when 206
necessary. 207
6.4.5.3 Compliance criteria 208
Rationale: Material flammability requirements are checked by the testing of Annex S, 209
by compliance with the component document or through review of material 210
data sheets. 211
6.4.6 Control of fire spread in a PS3 circuit 212
Source: IEC 60950-1 213
Rationale: There are two basic requirements to control the spread of fire from PS3 214
circuits: 215
a) use of materials within the fire enclosure that limit fire spread. This 216
includes the same requirements as for components in PS2 circuits and 217
includes a requirement from IEC 60950-1 to address all combustible 218
materials that are found within the fire enclosure; 219
b) use fire-containing enclosures – Product enclosures will have a 220
design capable of preventing the spread of fire from PS 3 circuits. The 221
criteria for fire enclosures is based on the available power. 222
Rationale: PS3 sourced circuits may contain a significant amount of energy. During 223
single fault conditions, the available power may overwhelm the 224
safeguard of material control of fuels adjacent to the fault or any 225
consequential ignition source making a fire enclosure necessary as part of 226
the supplementary safeguard. A fire enclosure and the material controls 227
constitute the necessary supplementary safeguard required for a PS3 228
circuit. 229
Use adequate materials, typically permitting material pre -selection of non-230
combustible or flame-resistant materials for printed wiring and 231
components in or near PS3. Only fuels that would contribute significant fuel 232
to a fire are considered. This implies compliance with all the requirements 233
for PS2 circuits and in addition, application of a fire containing enclosure. 234
Material flammability requirements for all materials inside a fire enclosure 235
are included in this clause. This model has been used historically in 236
IEC 60950-1 to control the amount and type of fuel that may become 237
engaged in a significant fire. Because there is no single fault tes ting when 238
applying this method, a significant ignition source may engage other fuels 239
located inside the fire enclosure. PS3 circuits, particularly higher power 240
PS3 circuits can create significant internal fires if adjacent combustible 241
materials, not directly associated with a circuit, become involved in an 242
internal fire. These fires, if unmitigated , can overwhelm the fire 243
enclosures permitted in this document. Control of material flammability of 244
fuels located within the enclosure should be sufficient based on historical 245
experience with IEC 60950-1. 246
The exceptions provided in this clause for small parts, consumable 247
material, etc. that are inside of a fire enclosure, mechanical components 248
that cannot have flame retardant properties are exempt from the materia l 249
flammability requirements. This is the current practice in IEC 60950-1. 250
Components filling openings in a fire enclosure that are also V-1 are 251
considered adequate, as it is impractical to further enclose these devices. 252
These constructions are commonly used today in IT and CE products. 253
IEC TR 62368-2:20xx © IEC 2019 – 95 –
Wiring already has requirements in a separate part of this clause. 254
Motors and transformers have their own flammability spread requirements 255
and as such do not need a separate enclosure (see G.5.3 and G.5.4). 256
6.4.7 Separation of combustible materials from a PIS 257
Rationale: Where potential ignition sources are identified through classification and 258
single fault conditions , separation from the ignition source by distance 259
(material controls) or separation by barriers are used to li mit the spread of 260
fire from the ignition source and are necessary to ensure the ignition is not 261
sustained. 262
6.4.7.2 Separation by distance 263
Source: IEC 60065 264
Rationale: The safeguard for materials within the fire cone includes material size 265
control (and including prohibition on co-location of flammable parts). 266
Otherwise the parts close to the PIS shall be material flammability class 267
V-1, which limits sustained ignition and spread. 268
Small parts (less than 4 g) are considered too small to significantly 269
propagate a fire. This value is also used for components used in PS2 and 270
PS3 circuits. It has been used in IEC 60065 with good experience. 271
Where these distances are not maintained, a needle flame test option is 272
included with 60 s needle flame application based on previous 273
requirements in IEC 60065. This alternative to these distance requirements 274
(the needle flame test) can be performed on the barrier to ensure that any 275
additional holes resulting from the test flame are still compliant (openings 276
that will limit the spread of fire through the barrier). 277
Redundant connections: An arcing PIS cannot exist where there are 278
redundant or reliable connections as these connections are considered not 279
to break or separate (thereby resulting in an arc). 280
Redundant connections are any kind of two or more connections in parallel, 281
where in the event of the failure of one connection, the remaining 282
connections are still capable of handling the full power. Arcing is not 283
considered to exist where the connections are redundant or otherwise 284
deemed not likely to change contact resistance over time or through use. 285
Some examples are given, but proof of reliable connections is left to the 286
manufacturer and there is no specific criteria that can be given: 287
– Tubular rivets or eyelets that are addit ionally soldered – this assumes 288
that the riveting maintains adequate contact resistance and the 289
soldering is done to create a separate conductive path. 290
– Flexible terminals, such as flexible wiring or crimped device leads that 291
remove mechanical stress (due to heating or use) from the solder joint 292
between the lead and the printed wiring trace. 293
– Machine or tool made crimp or wire wrap connections – well-formed 294
mechanical crimps or wraps are not considered to loosen. 295
– Printed boards soldered by auto-soldering machines and the auto-296
soldering machines have two solder baths , but they are not considered 297
reliable without further evaluation. This means most printed boards 298
have been subjected to a resoldering process. But there was no good 299
connection of the lead of the component(s) and the trace of the printed 300
board in some cases. In such cases, resoldering done by a worker by 301
hand may be accepted. 302
– 96 – IEC TR 62368-2:20xx © IEC 2019
Combustible materials, other than V-1 printed wiring boards are to be 303
separated from each PIS by a distance based on the size of resulting 304
ignition of the PIS. The flame cone dimensions 50 mm and 13 mm 305
dimensions were derived from IEC 60065, where they have been used for 306
several years with good experience. The area inside the cone is 307
considered the area in which an open flame can exist and where material 308
controls should be applied. 309
Resistive potential ignition sources are never a point object as presented 310
in Figure 37 of IEC 62368-1. They are more generally three-dimensional 311
components, however only one dimension and two-dimension drawings are 312
provided. The three-dimensional drawing is difficult to understand and 313
difficult to make accurate. 314
Figure 34 in this document shows how to cope with potential ignition 315
sources that are 3D volumes. This drawing does not include the bottom 316
part of the fire cone. The same approach should be used for the bottom 317
side of the part. 318
Figure 34 – Fire cone application to a large component
The fire cone is placed at each corner. The locus of the outside lines 319
connecting each fire cone at both the top and the base defines the 320
restricted volume. 321
Figure 37 Minimum separation requirements from a PIS 322
This drawing of a flame cone and its dimensions represents the one-323
dimension point ignition source drawn in two dimensions. The three-324
dimension envelope (inverted ice cream cone) of a flame from a potential 325
ignition source. This PIS is represented as a point source in the drawing 326
for clarity, however these PISs are more often three-dimensional 327
components that include conductors and the device packaging. 328
Figure 38 Extended separation requirements from a PIS 329
A two-dimensional representation of an ignition source intended to provide 330
more clarity. 331
6.4.7.3 Separation by a fire barrier 332
Source: IEC 60065 333
IEC TR 62368-2:20xx © IEC 2019 – 97 –
Rationale: The use of flame retardant printed wiring is considered necessary as the 334
fuel and the electrical energy source are always in direct contact. V -1 has 335
historically been adequate for this purpose. 336
Printed wiring boards generally di rectly support arcing PIS and as such, 337
cannot be used as a barrier. There is a potential that small openings or 338
holes may develop, thus permitting the arc to cross through the board. 339
A printed board can act as a barrier for an arcing PIS, provided the PIS is 340
not directly mounted on the board acting as a barrier. 341
For resistive PIS, printed wiring boards can be used provided they are of 342
V-1 or meet the test of Clause S.1. Any V-1 and less-flammable fuels are 343
required to minimize the possibility flammable mate rial falling onto the 344
supporting surface or contact with combustible fuels (resulting in pool 345
fires). If a PIS is located on a board and supplied by a PS2 or PS3 source, 346
there should be no other PS2 or PS3 circuits near the PIS, as this could 347
create faults due to PIS heating that was not otherwise considered. 348
Figure 39 Deflected separation requirements from a PIS when a fire barrier is used 349
This figure demonstrates the change on the fire cone when there is a fire 350
barrier used to separate combustible material from a potential ignition 351
source. This drawing was retained as an example application for only two 352
angles. Recognizing that many examples are possible, only two are kept 353
for practical reasons. History with multiple drawings of barriers in varying 354
angles could be difficult to resolve. The fire team decided to keep only two 355
drawings with an angle barrier as representative. 356
6.4.8 Fire enclosures and fire barriers 357
Rationale: The safeguard function of the fire enclosure and the fire barrier is to 358
impede the spread of fire through the enclosure or barrier (see Table 13 359
in this document). 360
– 98 – IEC TR 62368-2:20xx © IEC 2019
Table 13 – Fire barrier and fire enclosure flammability requirements 361
Flammability requirements
Fire barrier
6.4.8.2.1
Fire barrier requirements
Non-combustible material or
Needle flame test Clause S.1 or V-1 class material or VTM-1 class material
6.4.8.4
Separation of a PIS to a fire barrier
– Distance 13 mm to an arcing PIS and
– Distance 5 mm to a resistive PIS
Smaller distances are allowed provided that the part of the fire barrier complies with one of the following :
– Needle flame Clause S.2; After the test no holes bigger than in 6.4.8. 3.3 and 6.4.8.3.4 allowed or
– V-0 class material
Fire enclosure
6.4.8.2.2
Fire enclosure materials:
– Non-combustible, or
– For PS3 ≤ 4 000 W, needle flame test Clause S.1 or V-1 class material
– For PS3 > 4 000 W, needle flame test Clause S.5 or 5VB class material
Component materials which fill an opening in a fire enclosure or intended to be mounted in such opening
– Comply with flammability requirements of relevant IEC component document; or
– V-1 class material ; or
– needle flame test Clause S.1
6.4.8.4
Separation of a PIS to a fire enclosure
– Distance 13 mm to an arcing PIS and
– Distance 5 mm to a resistive PIS
Smaller distances are allowed , provided that the part of the fire enclosure complies with one of the following :
– Needle flame Clause S.2; After the test no holes bigger than in 6.4.8. 3.3 and 6.4.8.3.4 allowed; or
– V-0 class material
362
6.4.8.2.1 Requirements for a fire barrier 363
Source: IEC 60065, IEC 60950-1 364
Rationale: Barriers used to separate PIS from flammable fuels reduce the abilit y of a 365
resulting PIS flame from impinging on flammable materials. This can be 366
achieved by using flame retardant materials that pass the performance test 367
in Clause S.1 or the pre-selection criteria of a minimum V-1 flame class. 368
The test in Clause S.1 is based on the needle flame test which is currently 369
an option for enclosure testing in both IEC 60950-1 and IEC 60065. 370
6.4.8.2.2 Requirements for a fire enclosure 371
Source: IEC 60065, IEC 60950-1 372
Rationale: The material flammability class V-1 was chosen as the minimum value 373
based on its historical adequacy, and recent testing done during the 374
development of the requirements for externally caused fire. 375
IEC 60950-1 – Prior requirements for 5 V class materials based on 376
product weight lacked sufficient rationale . This has been improved and 377
related to power available to a fault in this document. 378
IEC TR 62368-2:20xx © IEC 2019 – 99 –
IEC 60065 – V-2 class material performance during large scale test 379
reviewed by the fire team indicated inconsistencies in performance over a 380
range of different V-2 materials. The propensity for V-2 class materials to 381
create ‘pool’ fires is also detrimental to fire enclosure performance and 382
therefore not accepted unless it passes the end-product testing. 383
In addition to pre-selection requirements, an end-product test (material 384
test) is also included by reference to Clauses S.1 (for < 4 000 W) and S.5 385
(for 4 000 W). This test is based on the needle flame test which is 386
currently an option for enclosure testing in both IEC 60950-1 and 387
IEC 60065. 388
This power (4 000 W) separation is also used in the control of fire spread 389
method to delineate safeguard criteria for fire enclosure materials (V-1 390
versus 5 V). IEC 60950-1 has historically used weight to define fire 391
enclosure criteria and it was felt the use of available power was more 392
appropriate and generally reflective of current practice. 393
Both 5 VA and 5 VB class materials are considered acceptable for 394
equipment with power above 4 000 W. This is consistent with current 395
practice in IEC 60950-1. 396
6.4.8.2.3 Compliance criteria 397
Rationale: In each case there is a performance test, and construction (pre -selection) 398
criteria given. For material flammability, compliance of the material is 399
checked at the minimum thickness used as a fire enclosure or fire barrier. 400
6.4.8.3 Constructional requirements for a fire enclosure and a fire barrier 401
Rationale: Opening requirements for barriers and fire enclosure should limit the 402
spread of flame through any existing opening. A fire enclosure limits the 403
spread of fire beyond the equipment and is permitted to have holes (within 404
established limits). 405
6.4.8.3.1 Fire enclosure and fire barrier openings 406
Rationale: These requirements are intended to reduce the spread of an internal fuel 407
ignition through a fire enclosure or barrier. 408
Openings are restricted based on the location of each potential ignition 409
source using the flame cones or in the case of control fire spread, above 410
all PS3 circuits. 411
Figure 40 Determination of top, bottom and side openings 412
In the left figure, when the vertical surface has an inclination (angle) of less 413
than 5° from vertical, then only the side opening requirements of 6.4.8.3.5 414
apply. 415
In the right figure, when the vertical surface has an inclination (angle) of 416
more than 5° from the vertical, then the openings are subject to the 417
requirements for top openings of 6.4.8.3.3 or bottom openings of 6.4.8.3.4. 418
6.4.8.3.2 Fire barrier dimensions 419
Rationale: Edges can be more easily ignited than a solid surface. Barrier dimensions 420
shall also be sufficient to prevent ignition of the barrier edges. 421
Barriers made of non-combustible materials shall have edges that extend 422
beyond the limits of the fire cone associated with each potential ignition 423
source. If the barrier edge does not extend beyond the cone, then it is 424
assumed the edges may ignite. 425
Met opmerkingen [JR5]: See Raleigh minutes item 9.5.8
– 100 – IEC TR 62368-2:20xx © IEC 2019
6.4.8.3.3 Top openings and top opening properties 426
Source: IEC 60065 427
Rationale: Top opening drawings are restricted in the areas of likely flame 428
propagation to the side and above an ignition source. 429
Top openings are also considered to cover what has historically been 430
called side opening where the opening is above the horizontal plane 431
containing the ignition source. 432
The top/side openings that are subject to controls are only those within the 433
fire cone drawing (Figure 37) plus a tolerance of 2 mm, as shown in Figure 434
41. The application of the fire cone dimensions has been used in 435
IEC 60065 and proven historically adequate. 436
Control of openings above the flame cone is also not necessary given that 437
the heat transfer (convection) will follow the gases moving through those 438
openings and is not sufficient to ignite adjacent materials. If the openings 439
are directly blocked, the convection path will be blocked which would 440
restrict any heat transfer to an object blocking the opening. 441
Openings to the side of the fire cone dimensions were reviewed and 442
ultimately not considered necessary as the radiant heat pr opagation 443
through openings to the side of the ignition is very small. This radiant heat 444
is not considered sufficient to ignite adjacent materials given the 445
anticipated flame size and duration in AV and ICT products. 446
In this aspect, the virtual flame cone deflection as per Figure 39 need not 447
be considered since the actual needle flame application will cover that. 448
The test method option proposed provides a test option for direct 449
application of a needle flame. The test (S. 2) referred to in this clause is 450
intended to provide a test option where holes do not comply with the 451
prescriptive measures. S.2 is originally intended to test the material 452
flammability, but in this subclause the purpose of the test is to see the 453
potential ignition of outer material covering the openings, so application of 454
the needle flame is considered for that aspect rather than the burning 455
property of the enclosure itself. 456
Cheesecloth is used as a target material for the evaluation of flame spread 457
due to its flexible nature (ease of use) and its quick propensity to ignite. 458
The flame cone envelope is provided as a single point source. The 459
applicable shape and any affecting airflow are taken into account for 460
determining the whole shape of the PIS, not just a single point. The point is 461
applied from the top edge of the component being considered and , in 462
practice, it is rarely a single point. 463
The opening dimensions for the 5 mm and 1 mm dimensions have been 464
determined through test as being restrictive enough to cool combustible 465
gases as they pass through the openings and those mitigate any flame 466
from passing through the opening. Top openings properties are based on 467
tests conducted by the fire team with open flames (alcohol in a Petri dish) 468
that demonstrated these opening dimensions are adequate . 469
6.4.8.3.4 Bottom openings and bottom opening properties 470
Source: IEC 60065, IEC 60950-1 471
Rationale: The location of openings is restricted for barriers inside the flame cone of 472
Figure 37 and for enclosures, inside the cone and directly below to protect 473
against flammable drips from burning thermoplastic as shown in Figure 42. 474
The application of the fire cone dimensions has been used in IEC 60065 475
and proven historically adequate. 476
IEC TR 62368-2:20xx © IEC 2019 – 101 –
There are several options for opening compliance (see Table 14 in this 477
document). Flaming oils and varnishes are not common in ICT equipment 478
today. The performance test based on the hot flaming oil test, in use for 479
IEC 60950-1, have other opening options and are developed based on 480
lower viscosity materials (when burning). They are more commonly found 481
in ICT (that provide additional options ). 482
Clause S.3 (hot flaming oil test) is the base performance option and 483
provides a test option (hot flaming oil test) that historically has been 484
adequate for tests of bottom openings. 485
The values in items band c) come directly from IEC 60950-1 where they 486
have been historically adequate and have demonstrated compliance with 487
the S.3 performance testing. These requirements, previously from 488
IEC 60950-1, 4.6.2 Bottoms of fire enclosures, have been updated in the 489
third edition of IEC 62368-1. The IEC 60950-1 requirements are more 490
stringent than the new IEC 62368-1 requirements and may still be used as 491
an option without additional tests, which is likely since designs based on 492
the IEC 60950-1 requirements have been in use for some time. 493
The work done to validate top openings was also considered adequate for 494
bottom openings under materials of any properties (3 mm and 1 mm slots). 495
This requirement is less onerous than those found in IEC 60950-1 which 496
permitted NO openings unless they complied with the other options. 497
Openings under V-1 class materials (or those that comply with Clause 498
S.1) are controlled in the same manner as done in IEC 60950-1 which was 499
considered adequate however an additional option to use 2 mm slots of 500
unlimited length is also considered adequate. 501
The 6 mm maximum dimension relates to a maximum square opening 502
dimension of 36 mm2 and a round opening of 29 mm2. In IEC 60950-1 the 503
requirement was 40 mm2, which relates to a maximum 7 mm diameter if 504
round or 6,3 mm maximum if not round. 505
The only option where flammable liquids are used is to meet the 506
requirements of the hot flaming oil test ( Clause S.3). 507
An option for equipment that is installed in spe cial environments where a 508
non-combustible flooring is used (environmental safeguard) may obviate 509
the need for an equipment bottom safeguard. This is current practice in 510
IEC 60950-1 where equipment is used in “restricted access locations”. 511
Baffle plate constructions were added, as they have been used in 512
IEC 60950-1 and have proven to be an acceptable solution. 513
– 102 – IEC TR 62368-2:20xx © IEC 2019
Table 14 – Summary – Fire enclosure and fire barrier material requirements 514
Parameters Fire barrier Fire enclosure
Input < 4 000 W Input 4 000 W
Co
mb
us
tib
le m
ate
ria
l:
Separation from PIS
13 mm or more from arcing PIS
5 mm or more from resistive PIS
Note: exceptions may apply
Dimensions Sufficient to prevent ignition of the edges
Not applicable
Flammability
a) Test S.1; or
b) V-1; or
c) VTM-1
a) Test S.1; or
b) V-1
a) Test S.5; or
b) 5 VA; or
c) 5 VB
No
n-
Co
mb
us
tib
le
ma
teri
al:
Acceptable
Top openings See 6.4.8.3.3
Bottom openings See 6.4.8.3.4
515
6.4.8.3.5 Side opening and side opening properties 516
Source: IEC 60950-1 517
Rationale: For Edition 3, IEC TC 108/WG HBSDT agreed to adopt from 518
IEC 60950-1:2005 (4.6.1, 4.6.2 and Figure 4E) the principles and criteria 519
for determination of suitable side openings using a five (5) degree 520
projection. The primary rationale for a dopting these principles was the 521
demonstration of many years of a solid safety record of use for ITE with 522
IEC 60950-1. However, one issue that had to be resolved was that in 523
IEC 60950-1 the 5-degree projection of Figure 4E was always made from 524
the outer surface of a combustible internal component or assembly rather 525
than a defined potential ignition source (PIS), typically a metallic circuit 526
inside the component. The PIS principle was not inherent to IEC 60950-1. 527
For example, in a component or assembly, el ectrical or not, made of 528
combustible material that might ignite within a f ire enclosure, the 5-degree 529
projection was made from the surface of the component or assembly 530
closest to the side enclosure and not from a metallic circuit inside the 531
component or subassembly that could be a potential source of ignition. 532
Therefore, for example, if a printed board was considered the 533
component/subassembly likely to ignite, the 5-degree projection was made 534
from the edge of the printed board and not the current carrying t race, which 535
in IEC 62368-1 is the PIS. In some cases throughout the history of 536
IEC 60950-1, this distance from the metallic trace to component edge could 537
have been up to several centimetres. 538
IEC TR 62368-2:20xx © IEC 2019 – 103 –
However, when IEC TC 108/WG HBSDT considered the common 539
construction of internal components and subassemblies likely to be 540
associated with a PIS, including printed boards, it was determined that it 541
was reasonable to assume that in modern AV/ICT equipment the distance 542
between the PIS and the outer edge of a component or sub-assembly was 543
likely to have negligible impact on the overall fire safety of the product, in 544
particular in the application of the 5 degree principle. Due to general 545
miniaturization of products, material cost optimization, and modern design 546
techniques (including CAD/CAM), printed boards and other electronic 547
components and assemblies associated with a PIS typically do not use 548
unnecessary amounts of combustible materials – modern printed boards 549
more typically now have metallic traces very close to the board edge rather 550
than many millimetres away. 551
As a result IEC TC 108/WG HBSDT considered that the IEC 60950-1 five 552
(5) degree projection principle for side openings remained sound even if 553
projected from the actual PIS rather than the edge of combustible mater ial 554
associated with the PIS. This view also is consistent with the Note to 555
Figure 38, Extended separation requirements from a PIS, which states, for 556
a resistive PIS “…measurements are made from the nearest power 557
dissipating element of the component involved. If in practice it is not readily 558
possible to define the power dissipating part, then the outer surface of the 559
component is used.” 560
6.4.8.3.6 Integrity of a fire enclosure 561
Source: IEC 60950-1 562
Rationale: The clause ensures that a fire enclosure where required, is assured to 563
remain in place and with the product through either an equipment or 564
behavioural safeguard. This requirement is a service condition safeguard 565
for ordinary persons to ensure that a fire enclosure (if required) is 566
replaced prior to placing the equipment back into use. This safeguard is 567
also required in IEC 60950-1. 568
6.4.8.3.7 Compliance criteria 569
Rationale: In each case, there is a performance test, and construction (pre -selection) 570
criteria given. 571
6.4.8.4 Separation of a PIS from a fire enclosure and a fire barrier 572
Source: IEC 60065, IEC 60950-1 573
Rationale: Non-metallic fire enclosures and fire barriers may not be sufficient to limit 574
the spread of fire where an enclosure is close or in direct contact with a 575
potential ignition source. 576
The 13 mm and 5 mm distances were used in IEC 60065 to prevent an 577
ignition source from transferring sufficient energy to adjacent flame-578
retardant V-1 barriers. These distances are intended to reduce the 579
likelihood of melting or burn-through of the barrier of fire enclosure. 580
Where these distances are not maintained, a needle flame test option is 581
included with 60 s needle flame application based on work in IEC 60065. 582
Openings following the needle flame test were discussed with criteria 583
being: 584
a) no additional opening, 585
b) no enlargement of existing holes, 586
c) compliance with the fire enclosure opening requirements. 587
Due to test repeatability, the criteria of a) are considered most readily 588
reproduced. 589
– 104 – IEC TR 62368-2:20xx © IEC 2019
The option to use V-0 or 5 V class materials without distance or thickness 590
requirements is based on historical practices in IEC 60065 and 591
IEC 60950-1 where no distance requirements were applied. 592
The material thickness requirements where ignition sources are in close 593
proximity to a barrier were not included based on dis cussions in 594
IEC TC 108 and current practice for IEC 60950-1 enclosures. There is fire 595
test data (barrier testing from IEC 60065) indicating that 2 mm thick (or 596
greater) V-0 barriers and 5 VA barriers have sufficient flame resistance to 597
minimize a risk of creating openings when used in direct contact with PIS’s. 598
Good HWI or HAI tests are not available internationally to address the 599
distance from ignition sources to fire enclosure and barriers. The fire team 600
has chosen to use the needle flame test as a surrog ate test (similar to that 601
done for barriers). 602
6.5.1 General requirements 603
Source: IEC 60332-1-2, IEC 60332-2-2 604
Rationale: Wiring flammability proposals have now been included for all wiring 605
(external and internal). 606
Compliance with IEC 60332-1-2 for large wires and IEC 60332-2-2 for 607
small wires has historically proven adequate for mains wiring. These 608
documents include their own material flammability requirements. 609
The requirements of IEC TS 60695-11-21 are also considered adequate 610
given that the flame spread requirements for vertical testing are more 611
onerous than the IEC 60332 series of documents. 612
The compliance criteria are based on application of the above test 613
methods. These are consistent with international wiring standards. National 614
standards may have more onerous requirements. 615
6.5.2 Requirements for interconnection to building wiring 616
Source: IEC 60950-1:2005 617
Rationale: Externally interconnected circuits that are intended for connection to 618
unprotected building wiring equipment can receive sufficient pow er from 619
the product to cause ignition and spread of fire with the building wall, 620
ceiling, or remotely interconnected equipment. These requirements limit the 621
power available to connectors/circuits intended for interconnection to 622
specific types of wiring where the product is responsible for protection of 623
that wiring. 624
Where a circuit is intended for connection to equipment that is directl y 625
adjacent to the equipment, 6.6 prescribes the appropriate safeguards and 626
limits associated for PS2 and PS3 sources. 627
Telecommunication wiring is designed based on the expected power from 628
the network. The requirements of IEC 60950-1 were considered adequate 629
and were included. Wiring in this application should be equivalent to 0,4 630
mm diameter wiring (26 AWG) and have a default 1,3 A current limit 631
established. This value has been used in IEC 60950-1 for the smaller 632
telecommunication wiring. 633
For some building wiring, the PS2 and PS3 safeguards are not considered 634
adequate in some countries for connection to building wiring where tha t 635
wiring is run outside of the conduit or other fire protective enclosures. The 636
requirements for this clause come directly from requirements in IEC 60950-637
1, 2.5 for circuits identified as limited power circuits. These requirements 638
have proven to be historically adequate for connection of IT equipment to 639
building wiring in these jurisdictions. 640
The values used and protection requirements included in IEC 60950-1 and 641
included in Annex Q.1 came from the building and fire codes requiring this 642
protection. 643
IEC TR 62368-2:20xx © IEC 2019 – 105 –
These requirements do not apply to connectors/circuits intended for 644
interconnection of peripheral equipment used adjacent to the equipment. 645
This requirement is also important for the use of ICT equipment in 646
environments subject to electrical codes such as Natio nal Fire Protection 647
Association NFPA 70, which permit the routing of low power wiring outside 648
of a fire containment device. 649
Annex Q.1 was based on requirements from IEC 60950-1 that are designed 650
to comply with the external circuit power source requirements necessary 651
for compliance with the electrical codes noted above. 652
6.6 Safeguards against fire due to the connection of additional equipment 653
Source: IEC 60950-1 654
Rationale: This subclause addresses potential fire hazards due to the connection of 655
accessories or other additional equipment to unknown power source 656
classifications. Most common low-voltage peripherals are not evaluated for 657
connection to PS3 and therefore power sources should be identified. This 658
is a current requirement of IEC 60950-1. 659
Where the interconnected devices are known (device requirements are 660
matched to the appropriate power source), this requirement for safeguard 661
is not necessary. 662
___________ 663
7 Injury caused by hazardous substances 664
Rationale: The majority of chemical injuries arise from inhalation or ingestion of 665
chemical agents in the form of vapours, gases, dusts, fumes and mists, or 666
by skin contact with these agents (see Table 15 in this document). The 667
degree of risk of handling a given substance depends on the magnitude 668
and duration of exposure. These injuries may be either acute or chronic. 669
Many resins and polymers are relatively inert and non -toxic under normal 670
conditions of use, but when heated or machined, they may decompose to 671
produce toxic by-products. 672
Toxicity is the capacity of a material to produce injury or harm when the 673
chemical has reached a sufficient concentration at a certain site in the 674
body. 675
Potentially hazardous chemicals in the equipment are either: 676
– as received in consumable material or items, such as printer 677
cartridges, toners, paper, cleaning fluids, batteries; 678
– produced under normal operating conditions as a by-product of the 679
normal function of the device (for example, dust from paper handling 680
systems, ozone from printing and photocopying operations, and 681
condensate from air conditioning/de-humidifier systems); or 682
– produced under abnormal operating conditions or as a result of a 683
fault. 684
It is essential to: 685
– determine what substances are present in relative amounts in t he 686
equipment or could be generated under normal operating conditions ; 687
and 688
– minimize the likelihood of injury to a person due to interaction with 689
these substances. 690
NOTE In addition to their potential toxicity, loss of containment of chemical materials may 691 cause or contribute to failure of safeguards against fire, electric shock, or personal injury 692 due to spillages. 693
– 106 – IEC TR 62368-2:20xx © IEC 2019
The number of different chemical materials that may be used in the wide 694
variety of equipment covered by this document makes it impossible to 695
identify specific hazards within the body of this document. Information 696
needs to be sought by equipment manufacturers from the material 697
suppliers on the hazards associated with their products and their 698
compliance with any national and/or governmental regulati ons on the use 699
and disposal of such materials. 700
Energy source: 701
The energy source for most chemically -caused injuries is ultimately the 702
ability of a material to chemically react with human tissue, either directly or 703
indirectly. The exception would be inert m aterials that can damage tissues 704
by preventing them from functioning by limiting certain chemical reactions 705
necessary for life. An example of this would be types of dust, which do not 706
react with lung tissue, but prevent air from reaching the bloodstream. T he 707
reactions may be very energetic and damaging, such as acids on the skin, 708
or can be very slow, such as the gradual build -up of substances in human 709
tissues. 710
Transfer mechanism: 711
Transfer can only occur when chemical energy makes contact with human 712
tissue. The routes for contact with human tissue are through the skin [or 713
any outer membrane such as the eyes or nasal lining] (absorption), through 714
the digestive tract (digestion), or through the lungs (inhalation). The route 715
taken will depend largely on the phys ical form of the chemical: solid, liquid, 716
or gas. 717
Injury: 718
An injury can be either acute or chronic. Acute injuries are injuries with 719
immediate and serious consequences (for example, a strong acid in the 720
lungs) or the injury can be mild and result in irrita tion or headache. Chronic 721
injuries are injuries with long term consequences and can be as serious as 722
acute injuries (for example, consequences of long-term exposure to 723
cleaning solvents). 724
In most cases, the difference is the quantity and lethality of the t oxic 725
substance. A large amount of acetone can lead to death; a small amount 726
may simply result in a headache. Many chemical compounds essential to 727
life in small quantities (for example, zinc, potassium and nickel) can be 728
lethal in larger amounts. The human body has different degrees of 729
tolerance for different hazardous chemical substances. Exposure limits 730
may be controlled by government bodies for many chemical substances. 731
Where the use of hazardous chemical substances in equipment cannot be 732
avoided, safeguards shall be provided to reduce the likelihood of 733
exceeding the exposure limits. 734
The different types of chemical hazards are identified in Table 15 and 735
Figure 35 in this document demonstrating the hierarchy of hazard 736
management. 737
IEC TR 62368-2:20xx © IEC 2019 – 107 –
Table 15 – Control of chemical hazards 738
Transfer mechanism Prevention / safeguards
Ingestion, inhalation, skin contact, or other exposure to potentially hazardous chemicals
Hierarchy of hazard management:
1. Eliminate the chemical hazard by avoiding the use of the chemical.
2. Reduce the chemical hazard by substitution of a less hazardous chemical.
3. Minimize the exposure potential of the chemical by containment, ventilation and/or reduced quantities of the chemicals.
4. Use of personal protective equipment (PPE).
5. Provide use information and instructional safeguards.
Exposure to excessive concentrations of ozone during equipment operation
Hierarchy of hazard management:
1. Where possible, minimize the use of functions that produce ozone.
2. Provide adequate room ventilation.
3. Provide filtration to remove ozone.
Explosion caused by chemical reaction during use
Hierarchy of hazard management:
1. Eliminate the explosive charge.
2. Reduce the amount of explosive charge to the least amount possible.
3. Minimize hazard by the means of vents.
4. Provide use information and instructional safeguards.
739
740
– 108 – IEC TR 62368-2:20xx © IEC 2019
741
Figure 35 – Flowchart demonstrating the hierarchy of hazard management 742
743
IEC TR 62368-2:20xx © IEC 2019 – 109 –
Chemical hazards may also degrade or destroy the safeguards provided 744
for other hazards such as fire and electric shock (for example, ozone attack 745
on electrical insulation or corrosion of metallic parts). Chemical spillages or 746
loss of containment can also lead to other hazards such as electric shock 747
or fire depending on the location of any spillage and proximity to electric 748
circuits. The same methods used for chemical health exposure control 749
should also protect against such liquid spillages. 750
Using a hazard-based engineering approach, Figure 36 in this document 751
shows the main types of chemical health hazards and their transfer 752
mechanisms. 753
754
Figure 36 – Model for chemical injury 755
_____________ 756
8 Mechanically-caused injury 757
8.1 General 758
Rationale: Mechanically caused injury such as cuts, bruises, broken bones, etc., may 759
be due to relative motion between the body and accessible parts of the 760
equipment, or due to parts ejected from the equipment colliding with a 761
body part. 762
8.2 Mechanical energy source classifications 763
Purpose: To differentiate between mechanical energy source levels for normal 764
operating conditions, abnormal operating conditions and single fault 765
conditions applicable to each type of person. 766
8.2.1 General classification 767
Table 35 Classification for various categories of mechanical energy sources 768
Line 3 – Moving fan blades 769
Rationale: The acceptance criteria is based upon any number of factors such as 770
location, but the key factor for judging acceptance is based upon the K 771
factor, the relationship between mass (m) in kg, radius ( r) in mm and speed 772
(N) in rpm. This relationship can be used to find the K factor for the fan. 773
Fans with a low K factor and low speeds are considered safer. See 774
Figure 45 and Figure 46 for MS1 values. An MS2 fan requires an 775
instructional safeguard in addition to the limitation on the K factor value 776
and the speed of the fan. The need for the relevant safeguard is based on 777
the classification of fans. The K factor formula is taken from the UL 778
standard for fans, UL 507 (which is based on a University of Waterloo 779
study of fan motors). 780
Single fault condition on a fan includes, but is not limited to, 781
inappropriate input voltage due to the fault of a voltage regulator located 782
upstream. 783
– 110 – IEC TR 62368-2:20xx © IEC 2019
As plastic fan blades are regarded less hazardous than metal fan blades, 784
different values are used to determine separation between energy class 2 785
and class 3. 786
Typical parameters for fans used in products covered by this document are 787
as follows: 788
fan mass (m) = about 25 g or 0,025 kg; 789
fan diameter (r) = 33 mm; 790
fan speed (N) = 6 000 rpm (maximum speed when the system is hottest, 791
slower if the system is cool) . 792
Line 4 – Loosening, exploding or imploding parts 793
Rationale: IEC TC 108 has tried to come up with specific requirements for solid 794
rotating media. However, the result became too com plex to be useful at 795
this time. 796
Line 5 – Equipment mass 797
Rationale: The values chosen align with some commonly used values today. However, 798
it is noticed that these are not completely r eflecting reality and not a very 799
good hazard-based approach. IEC TC 108 plans to work on these values in 800
the future. 801
Line 6 – Wall/ceiling or other structure mount 802
Rationale: The values chosen align with some commonly used values today. However, 803
it is noticed that these are not completely reflecting reality and not a very 804
good hazard-based approach. IEC TC 108 plans to work on these values in 805
the future. 806
Notes b and c 807
Rationale: The current values are based on experience and basic safety publications. 808
8.2.2 MS1 809
Rationale: Safe to touch. No safeguard necessary. 810
8.2.3 MS2 811
Rationale: Contact with this energy source may be painful, but no injury necessitating 812
professional medical assistance occurs, for example, a small cut, abrasion 813
or bruise that does not normally require professional medical attention. A 814
safeguard is required to protect an ordinary person. 815
8.2.4 MS3 816
Rationale: An injury may occur that is harmful, requiring professional medical 817
assistance. For example, a cut requiring stitches, a broken bone or 818
permanent eye damage. A double or reinforced safeguard is required to 819
protect an ordinary person and an instructed person. 820
8.3 Safeguards against mechanical energy sources 821
Purpose: To determine the number of safeguards needed between the type of 822
person and the relevant energy source classification. 823
Rationale: An instructional safeguard describing hazard avoidance may be 824
employed to circumvent the equipment safeguard permitting access to 825
MS2 part locations to perform an ordinary person service function. The 826
instructional safeguard indicates that the equipment safeguard be 827
restored after the service activity and before power is reconnected. When 828
an instructional safeguard is allowed, a warning is also required to 829
identify insidious hazards. 830
IEC TR 62368-2:20xx © IEC 2019 – 111 –
For an instructed person and a skilled person, an instructional 831
safeguard, in the form of a warning marking, is necessary to supplement 832
the instruction they have received to remind them of the location o f hazards 833
that are not obvious. 834
However, for a skilled person, an equipment safeguard is required in the 835
service area of large equipment with more than one level 3 energy sources, 836
where the skilled person can insert their entire head, arm, leg or complete 837
body. This safeguard is intended to protect the skilled person against 838
unintentional contact with any other level 3 energy source due to an 839
involuntary startle reaction to an event in the equipment while servicing 840
intended parts. 841
The involuntary reaction may occur for a number of reasons, such as an 842
unexpected loud noise, an arc flash or receipt of a shock, causing the 843
person to recoil away from the energy source or part being serviced. 844
Where more than one of the level 3 energy sources may require servicing 845
at some time, removable equipment safeguards shall be designed such 846
that any level 3 sources not being serviced can remain guarded. The 847
equipment safeguards for this purpose only need to protect against larger 848
body contact, since the potential involuntary recoil reaction will likely be full 849
limb or body and not small body parts. 850
8.4 Safeguards against parts with sharp edges and corners 851
Rationale: Engineering judgment shall be used to class a mechanical energy source 852
as MS1, MS2 or MS3 and an appropriate safeguard shall be provided. 853
Where a MS2 or MS3 cannot be fully guarded without interfering with the 854
intended function of the equipment, it shall be guarded as much as 855
practical. Such an energy source shall not be accessible to children and 856
be obvious to an adult. Instructional safeguards shall be provided to warn 857
the person about potential contact with the energy source and what steps 858
to take to avoid unintentional contact. 859
We rely on engineering judgment as there are too many variables involved 860
to define the type of edge or corner combined with the applied force and 861
direction of contact or to provide specific values. 862
8.5 Safeguards against moving parts 863
Rationale: Enclosures and barriers protect against access to hazardous moving 864
parts. See 8.5.1 for the exception of requirements related to parts not fully 865
guarded because of their function in the equipment. 866
8.5.1 Requirements 867
Rationale: The MS2 or MS3 energy sources need to be guarded against accidental 868
access by a person's extremities, jewellery that may be worn, hair and 869
clothing, etc. Access is determined by applying the appropriate tool from 870
Annex V, and no further testing is necessary. We note that while it may be 871
technically possible for some jewellery and hair to enter an opening smaller 872
than the test finger, in such cases, the jewellery strands would have to be 873
very thin and flexible enough to enter (as would a few strands of hair). As 874
such while some pain may result if they hap pen to be caught in the 875
mechanical device, it is deemed unlikely an injury would occur as 876
described by this document. The residual risk can be considered a MS2 877
energy source at most. 878
– 112 – IEC TR 62368-2:20xx © IEC 2019
8.5.4.3 Equipment having an electromechanical device for destruction of media 879
Source: UL/CSA 60950-1 second edition [national difference] 880
Rationale: Recent large scale introduction of media shredders into the home 881
environment resulted in an increase of children being injured when 882
inserting their fingers through the shredder openings. These incidents were 883
studied and a new probe was developed to assess potential access by 884
children. The new probe/wedge has been desig ned for both application 885
with force when inserted into the shredder openings and assessment of 886
access to MS3 moving parts by a population consisting of both adults and 887
children. This design differs from the existing UL and IEC accessibility 888
probes since the UL Articulated Accessibility Probe is not intended to be 889
used with a force applied to it, and the current IEC probes, while having an 890
unjointed version for application under force, do not adequately represent 891
the population for both adults and children. 892
Because cross-cut shredders typically apply more force to the media than 893
straight-cut shredders, the requirements include differentiated application 894
forces for the two designs. The force values consider typical forces 895
associated with straight-cut and cross-cut designs, taking into account data 896
generated by the USA Consumer Product Safety Commission on typical 897
pull forces associated with both strip type and crosscut type shredders. 898
The dimensions of the new probe/wedge are based on the data generated 899
during the development of the UL Articulated Accessibility Probe. However, 900
the dimensions of the UL Articulated Accessibility Probe were defined in 901
consideration of causal handling of products. Because of this, the 95th 902
percentile points from the data were used to define the UL Articulated 903
Accessibility Probe. The thickness and length dimensions of the new 904
proposed probe/wedge have been developed in consideration of all data 905
points. Articulation points are identical to those for the UL Articulated 906
Accessibility Probe. 907
8.6 Stability of equipment 908
Source: IEC 60950-1 and IEC 60065 909
Purpose: To align existing practice with the MS1, MS2 and MS3 energy. 910
Rationale: Equipment weighing more than 25 kg is considered MS3. Regardless of 911
weight, equipment mounted to the wall o r ceiling is considered MS3 when it 912
is to be mounted above 2 m height. 913
Equipment weighing between 7 kg and not exceeding 25 kg is considered 914
MS2. Equipment with a weight of 1 kg or more and that is mounted to the 915
wall or ceiling to a maximum height of 2 m is also considered MS2. 916
Equipment with weight not exceeding 7 kg is considered MS1 if floor 917
standing, but can be either MS2 or MS3 if mounted to the wall or ceiling . 918
Also see carts and stands, and wall or ceiling mounted equipment . 919
Children are naturally attracted to moving images and may attempt to touch 920
or hold the image by pulling or climbing up on to the equipment. The tests 921
assess both the static stability and mounting grip when placed on a 922
slippery surface such as glass. Children might also misuse c ontrols that 923
are readily available to them. 924
8.6.2.2 Static stability test 925
Rationale: Equipment is assessed for stability during expected use by applying force 926
horizontally and downward on surfaces that could be used as a step or 927
have other objects placed upon it. 928
The value of 1,5 m was chosen as the maximum height where an average 929
person could lean on or against the product. 930
IEC TR 62368-2:20xx © IEC 2019 – 113 –
The 1,5 m is also used for table top equipment, since we do not know 931
whether the product is going to be placed on a table or, if so, what the 932
height of the table will be. 933
8.6.2.3 Downwards force test 934
Rationale: The height of 1 m represents the maximum height one could expect that 935
people could try to use as a step to reach something. 936
8.6.3 Relocation stability 937
Source: IEC 60950-1 and IEC 60065 938
Rationale: The 10° tilt test simulates potential horizontal forces applied to the 939
equipment either accidentally or when attempting to move the equipment. 940
In addition it simulates moving the equipment up a ramp during transport. 941
The test on the horizontal support may be necessary (for example, for 942
equipment provided with small feet, casters or the like). 943
8.6.4 Glass slide test 944
Source: IEC 60065:2011 945
Purpose: To address the hazard of equipment with moving images sliding off a 946
smooth surface when a child attempts to climb onto the equipment. 947
Rationale: To ensure the display does not slide too easily along a smooth surface that 948
could result in the display falling from an elevated height on to a child. 949
8.6.5 Horizontal force test and compliance criteria 950
Purpose: To simulate the force of a child climbing up on t o equipment with front 951
mounted user controls or with moving images. 952
Rationale: Field data and studies in the US have shown that children 2 -5 years of age 953
were attracted to the images on the display that may result in the child 954
climbing onto the display to touch/get close to the image. The equipment 955
could then tip over and crush the child. Also, products with accessible 956
controls or that are shorter than 1 m in height are considered likely to be 957
handled by children. 958
– Data was gathered in the 1986 to 1998 for CRT TV sets ranging from 959
48,26 cm to 68,58 cm (19 to 27 inches). The average horizontal force 960
was 13 % of the equipment weight. 961
– The 15° tilt test (an additional 5° over static stability test) provides an 962
additional safety factor. 963
8.7 Equipment mounted to a wall, ceiling or other structure 964
Source: IEC 60065 and 60950 series 965
Purpose: The objective of this subclause is to minimize the likelihood of injury 966
caused by equipment falling due to failure of the mounting means. 967
Rationale: Equipment intended to be mounted to a wall or ceiling should be tested to 968
ensure adequacy for all possible mounting options and all possible failure 969
modes. For typical equipment, such as flat panel televisions, mounting 970
bosses are usually integrated into the equipment and used with an 971
appropriate wall or ceiling mounting bracket to attach to a wall or ceiling. 972
Typical mounting bosses are comprised of threaded inserts into the rear 973
panel of the equipment. 974
The appropriate load is divided by the number of mounting means ( for 975
example, mounting bosses) to determine the force applied to each 976
individual mounting means. 977
The horizontal force values of 50 N and 60 s have been successfully used 978
for products in the scope of these documents for many years. 979
– 114 – IEC TR 62368-2:20xx © IEC 2019
8.7.2 Test methods 980
Figure 37 in this document gives a graphical view of the different tests 981
required by Test 2 and show the directions that the forces are applied . 982
983
Figure 37 – Direction of forces to be applied 984
Table 37 Torque to be applied to screws 985
Source: IEC 60065 986
Rationale: These torque values have been successfully used for products in the scope 987
of this document for many years. 988
8.8 Handle strength 989
Source: IEC 60065 and IEC 60950-1 990
Rationale: A handle is a part of the equipment that is specifically designed to carry the 991
equipment or subassembly around. A grip which is made for easy removal 992
or placement of a subassembly in an equipment is not considered to be a 993
handle. 994
The 75 mm width simulates the hand width. The safety factors take into 995
account the acceleration forces and additional stresses that could be 996
applied due to extra weight on top of the equipment when being lifted. The 997
safety factor is less at the higher weight ( MS3) because the equipment 998
would be lifted more slowly, reducing the acceleration force, and there is 999
less probability that extra weight would be added before lifting , as this 1000
would exceed the normal weight to be lifted by one person without 1001
assistance of a tool. Equipment classed as MS1 with more than one 1002
handle could be used to support additional objects when being carried and 1003
should be tested. 1004
8.8.2 Test method 1005
Rationale: There is no test for MS1 with only one handle. Having 2 handles facilitates 1006
transporting the equipment while carrying additional objects adding stress 1007
to the handles. 1008
8.9 Wheels or casters attachment requirements 1009
Purpose: To verify that wheels or casters are securely fixed to the equipment . 1010
Source: UL 1667 1011
IEC TR 62368-2:20xx © IEC 2019 – 115 –
Purpose: For wheel size, reduce the likelihood of the equipment on the cart or stand 1012
tipping while being moved from room to room where the wheels may 1013
encounter a variety of obstacles, such as: friction of different surfaces ( for 1014
example, transition from a hard surface over carpet edgi ng), cables, and 1015
doorway sills. 1016
Rationale: The 100 mm min wheel size was found to be adequate to enable rolling 1017
over these obstacles without abruptly stopping that could cause the cart or 1018
stand to tip, or the equipment located on the cart or stand to slide off. 1019
8.10 Carts, stands, and similar carriers 1020
Source: UL 60065 1021
Rationale: To avoid tipping, the 20 N test simulates cart wheels being unintentionally 1022
blocked during movement. 1023
8.10.1 General 1024
Source: IEC 60065 1025
Rationale: A wheel of at least 100 mm diameter can be expected to climb over usual 1026
obstacles such as electrical cords, door jambs , etc., and not be halted 1027
suddenly. 1028
8.10.2 Marking and instructions 1029
Rationale: Various means of marking may apply depending on the method of 1030
associating the equipment with a particular cart, stand of similar carrier. 1031
8.10.3 Cart, stand or carrier loading test and compliance criteria 1032
Source: IEC 60065 1033
Purpose: To verify that a cart or stand can withstand foreseeable overloading without 1034
creating a hazardous situation. 1035
Rationale: The 220 N force simulates the weight of a small child approximately 5 1036
years of age, who may attempt to climb onto the cart or stand. The 30 mm 1037
circular cylinder simulates a child’s foot. The 750 mm height is the 1038
approximate access height of the 5-year-old child. The additional 440 N 1039
force test simulates potential additional materials or equipment being 1040
placed on the cart or stand. The additional 100 N simulates overloading by 1041
the user. Testing has been limited to 1 min as experience has shown that 1042
the likelihood of a test failure will occur within that time. 1043
8.10.4 Cart, stand or carrier impact test 1044
Purpose: To verify that a cart or stand can withstand a foreseeable impact without 1045
creating a hazardous situation. 1046
Source: IEC 60065 and IEC 60950 series 1047
Rationale: The 7 joules simulate intentional and accidental contact with the equipment 1048
and come from the T.6 enclosure test. 1049
8.10.5 Mechanical stability 1050
Purpose: To verify that a cart or stand remains stable under specified loading. The 1051
equipment installed on the cart may come loose, but not fall off the cart. 1052
Rationale: The weight of the force test is reduced to 13 % should the equipment on 1053
the cart or stand move, as the equipment would then be considered 1054
separately from the cart or stand. When the equipment does not move 1055
during the force test, together they are considered a single u nit. 1056
8.10.6 Thermoplastic temperature stability 1057
Source: IEC 60065 and IEC 60950-1 1058
– 116 – IEC TR 62368-2:20xx © IEC 2019
Rationale: Intended to prevent shrinkage, relaxation or warping of materials that could 1059
expose a hazard. 1060
8.11 Mounting means for slide-rail mounted equipment (SRME) 1061
8.11.1 General 1062
Source: UL/CSA 60950-1 second edition 1063
Rationale: The potential hazardous energy source is a product that contains 1064
significant mass, and which is mounted on slide-rails in a rack. A joint 1065
US/Canadian Adhoc researched and developed these requirements based 1066
on hazard-based assessment and tests. 1067
The center of gravity was chosen to apply the downward force because in 1068
general, when installing equipment in a rack, it is foreseeable that 1069
previously installed equipment of similar size/mass may be pulled out into 1070
the service position (fully extended) and used to set the new equipment on 1071
while positioning and installing the new slide/rails. In this scenario, it is not 1072
likely that the new equipment would be significantly off -centre from the 1073
installed equipment that it is being set on. 1074
Vertically mounted SRMEs are not addressed in this document. 1075
8.11.3 Mechanical strength test 1076
Purpose: To simulate temporary placement of another server on to p of an existing 1077
one during installation of the new one. So the test is the downward force. 1078
Rationale: 50 % of the equipment mass is derived from the mass of the equipment, 1079
and a 50 % tolerance allowed for manufacturing differences in the rails 1080
which effectively adds a safety buffer. 1081
The 330 N to 530 N additional force accounts for equipment that is about to 1082
be installed in a rack being placed or set on a previously installed piece of 1083
equipment where the previously installed equipment is being used as a 1084
temporary shelf or work space. It is estimated that 530 N is the maximum 1085
mass of equipment allowed to be safely lifted by two persons without the 1086
use of mechanical lifting devices. Equipment having a mass greater than 1087
530 N will have mechanical lifting devices and it is therefore unlikely that 1088
the equipment being installed will be set on any equipment previously 1089
installed in the rack. 1090
Taking the actual installation environment into consideration, an additional 1091
force is limited to maximum 800 N (average weight of an adult man) that is 1092
same value as the downward test force in 8.6.2.3. The 800 N value comes 1093
from IEC 60950-1:2005, 4.1 Stability. 1094
8.11.3.2 Lateral push foce test 1095
8.11.3.3 Integrity of slide rail end stops 1096
Source: UL/CSA 60950-1 second edition 1097
Purpose: To simulate maintenance on the server itself, by smaller applying forces 1098
equivalent to what is expected during subassembly and card replacement, 1099
etc. So this also tests the laterally stability of the slide rails. It is not 1100
necessary to retest the downward vertical force if it is already tested for 1101
8.11.3, but that should be common sense when preparing a test plan. 1102
The cycling of the slide rail after the tests ensures they have not been bent 1103
in a way that could easily fly apart after the service operatio n. 1104
IEC TR 62368-2:20xx © IEC 2019 – 117 –
Rationale: The 250 N force is considered a force likely to be encountered during 1105
servicing of the equipment, and normal operations around equipment. The 1106
force is partially derived from the existing IEC 60950-1:2005, 4.1, and 1107
partially from research into normally encountered module plug forces seen 1108
on various manufacturers’ equipment. The application of force at the most 1109
unfavourable position takes into account the servicing of a fully extended 1110
piece of equipment, leaning on or bumping into an extended pi ece of 1111
equipment and other reasonably foreseen circumstances which may be 1112
encountered. 1113
___________ 1114
9 Thermal burn injury 1115
9.1 General 1116
Source: ISO 13732-1:2006 and IEC Guide 117 1117
Rationale: A General 1118
A burn injury can occur when thermal energy is conducted to a body part to 1119
cause damage to the epidermis. Depending on the thermal mass of the 1120
object, duration of contact and exposure temperature, the body response 1121
can range from perception of warmth to a burn. 1122
The energy transfer mechanism for equipment typically covered by the 1123
document is via conduction of thermal energy through physical contact with 1124
a body part. 1125
The likelihood of thermal injury is a function of several thermal energy 1126
parameters including: 1127
– temperature difference between the part and the body; 1128
– the thermal conductivity (or thermal resistance) between the hot part 1129
and the body; 1130
– the mass of the hot part; 1131
– the specific heat of the part material; 1132
– the area of contact; 1133
– the duration of contact. 1134
B Model for a burn injury 1135
A skin burn injury occurs when thermal energy impinges on the skin and 1136
raises its temperature to a level that causes cell damage. The occurrence 1137
of a burn will depend on several parameters. The hazard based three block 1138
model applied to the occurrence of a burn (see Figure 38 in this document) 1139
takes account of not just the temperature of the source, but its total thermal 1140
energy, which will depend on its temperature (relative to the skin), as well 1141
as its overall heat capacity. The model also takes account of the energy 1142
transfer mechanism, which will depend on the thermal conductivity between 1143
the body and the thermal source as well as the area and duration of 1144
contact. The occurrence and severity of a burn will depend on the amount 1145
of thermal energy transferred. 1146
1147
Figure 38 – Model for a burn injury 1148
– 118 – IEC TR 62368-2:20xx © IEC 2019
Normally, the energy transfer mechanism from the energy source to a body 1149
part is through direct contact with the body part and sufficient contact 1150
duration to allow transfer of thermal energy causing a burn. The higher the 1151
temperature of the thermal source and the more efficient the transfer 1152
mechanism, the shorter the contact time becomes before the occurrence of 1153
a burn. This is not a linear function and it is depend ent on the material, the 1154
temperature and the efficiency of the thermal transfer. The following 1155
examples demonstrate the impact of this non-linear relationship to short -1156
term/high temperature and longer term/lower temperature contact burns. 1157
Example 1: An accessible metal heat sink at a temperature of 60 °C may 1158
have sufficient energy to cause a burn after contact duration of about 5 s. 1159
At a temperature of 65 °C, a burn may occur after contact duration of just 1160
1,5 s (see IEC Guide 117:2017, Figure A.1). As the temperature of the 1161
metal surface increases, the contact time necessary to cause a burn 1162
decreases rapidly. 1163
Example 2: Consider a thermal source with low to moderate conductivity 1164
such as a plastic enclosure. At a temperature of 48 °C, it may take up to 1165
10 min for the transfer of sufficient thermal energy to cause a burn. At 1166
60 °C, a burn may occur after contact duration of just 1 min (see 1167
IEC Guide 117:2010, Table A.1). Although the temperature of the source 1168
has increased by just 25 %, the contact time necessary to cause a burn 1169
threshold has decreased by 90 %. 1170
In practice, the actual thermal energy and duration of exposure required to 1171
cause a burn will also depend on the area of contact and condition of the 1172
skin. For simplification of the model and based up on practice in the past, it 1173
is assumed that the contact area will be 10 % of the body and applied to 1174
healthy, adult skin. 1175
As a general rule, low temperature devices are likely to cause a heating or 1176
pain sensation before causing a significant burn to whi ch ordinary 1177
persons will normally respond (see ISO 13732-1:2009, Note of 5.7.3). 1178
Requirements for persons with impaired neurological systems are not 1179
considered in this document but may be considered in the future. 1180
NOTE 1 The impact of surface area contact is not being addressed in this paper at this 1181 time and is an opportunity for future work. Use and coverage of large contact areas as might 1182 occur in medical applications of heating pads covering more than 10 % of the body surface 1183 are outside the scope of thi s document, as this type of application is more appropriate to 1184 medical device publications. 1185
NOTE 2 The pressure of the contact between the thermal source and the body part can 1186 have an impact on the transfer of thermal energy. Studies have shown this effect to have 1187 appreciable impact at higher pressures. For typical pressures associated with casual 1188 contact up to a pressure of 20 N the effect has been shown to be negligible , and thus 1189 contact pressure is not considered in this document (Ref: ATSM C 1055, X1.2.3.4, ASTM C 1190 1057,7, Note 10). 1191
NOTE 3 Considerations for burns generated by infrared (IR), visible, ultra violet light 1192 radiation and RF radiation sources are outside the scope of Clause 9 dealing with thermal 1193 burn injury. 1194
C Types of burn injuries 1195
Burn injuries are commonly classed as first degree, second degree or third 1196
degree in order of increasing severity: 1197
First degree burn : the reaction to an exposure where the intensity or 1198
duration is insufficient to cause complete necrosis of the epidermis. The 1199
normal response to this level of exposure is dilation of the superficial blood 1200
vessels (reddening of the skin). No blistering occurs. (Reference: ASTM 1201
C1057) 1202
IEC TR 62368-2:20xx © IEC 2019 – 119 –
Second degree burn : the reaction to an exposure where the intensity and 1203
duration is sufficient to cause complete necrosis of the epidermis but no 1204
significant damage to the dermis. The normal response to this exposure is 1205
blistering of the epidermis. (Reference: ASTM C1057) 1206
Third degree burn : the reaction to an exposure where significant dermal 1207
necrosis occurs. Significant dermal necrosis with 75 % destruction of the 1208
dermis is a result of the burn. The normal response to this exposure is 1209
open sores that leave permanent scar tissue upon healing. 1210
(Reference: ASTM C1057) 1211
ISO 13732-1, 3.5 classifies burns as follows: 1212
Superficial partial thickness burn – In all but the most superficial burns, 1213
the epidermis is completely destroyed but the hair follicles and sebaceous 1214
glands as well as the sweat glands are spared. 1215
Deep partial thickness burn : a substantial part of the dermis and all 1216
sebaceous glands are destroyed and only the deeper parts of the hair 1217
follicles or the sweat glands survive. 1218
Whole thickness burn : when the full thickness of the skin has been 1219
destroyed and there are no surviving epithelial elements. 1220
Although there is some overlap between the classifications in ASTM C1057 1221
and those in IEC Guide 117, the individual classifications do not 1222
correspond exactly with each other. Further, it should be noted that the 1223
classifications of burns described here is not intended to correspond with 1224
the individual thermal source classifications (TS1, TS2, and TS3) describe d 1225
later in this document. 1226
D Model for safeguards against thermal burn injury 1227
To prevent thermally-caused injury, a safeguard is interposed between the 1228
body part and the energy source. More than one safeguard may be used 1229
to meet the requirements for thermal burn hazard protection. 1230
Figure 39 – Model for safeguards against thermal burn injury
To prevent thermally-caused injury, a safeguard is interposed between the 1231
body part and the energy source (see Figure 39 in this document). More 1232
than one safeguard may be used to meet the requirements for thermal 1233
burn hazard protection. 1234
Safeguards overview 1235
This section shows examples of the different types of safeguards that may 1236
be applied: 1237
a) Thermal hazard not present 1238
The first model, in Figure 40 in this document, presumes contact to a 1239
surface by an ordinary person where a thermal hazard is not present. In 1240
this case, no safeguard is required. 1241
– 120 – IEC TR 62368-2:20xx © IEC 2019
1242
Figure 40 – Model for absence of a thermal hazard 1243
b) Thermal hazard is present with a physical safeguard in place 1244
The second model, see Figure 41 in this document, presumes some 1245
contact with a surface by an ordinary person. The thermal energy source 1246
is above the threshold limit value for burns (Table 38 of 1247
IEC 62368-1:2018), but there are safeguards interposed to reduce the rate 1248
of thermal energy transferred such that the surface temperature will not 1249
exceed the threshold limit values for the expected contact durations. 1250
Thermal insulation is an example of a physical safeguard. 1251
1252
Figure 41 – Model for presence of a thermal hazard 1253
with a physical safeguard in place 1254
c) Thermal hazard is present with a behavioural safeguard in place 1255
The third model, see Figure 42 in this document, presumes the possibility 1256
of some contact to the thermal source or part by an ordinary person. The 1257
temperature is above the threshold limit value but the exposure time is 1258
limited by the expected usage conditions or through instructions to the user 1259
to avoid or limit contact to a safe exposure time. The contact time and 1260
exposure will not exceed the threshold limit value. An additional safeguard 1261
may not be required. 1262
1263
Figure 42 – Model for presence of a thermal hazard 1264
with behavioural safeguard in place 1265
9.2 Thermal energy source classifications 1266
Rationale: Surfaces that may be touched are classified as thermal ene rgy sources 1267
TS1, TS2 or TS3 with TS1 representing the lowest energy level and TS3 1268
the highest. The classification of each surface will determine the type of 1269
safeguards required. 1270
IEC TR 62368-2:20xx © IEC 2019 – 121 –
The assessment of thermal burn hazards is complex and, as discussed in 1271
the model for a burn injury above, involves several factors. Important 1272
aspects include the overall heat capacity of the source, its temperature 1273
relative to the body, thermal conductivity of the contact and others. To 1274
present a simple model for assessment of a given surface, it is assumed 1275
that the overall heat capacity and the thermal conductivity will remain 1276
constant. 1277
Thus, thermal energy sources are classified in terms of the material of the 1278
surface, its relative temperature and duration of contact only. Usuall y, for a 1279
given material the temperature and duration of contact are likely to be the 1280
only significant variables when assessing the risk of a burn injury. 1281
9.2.1 TS1 1282
Rationale: The lowest thermal energy source is TS1. TS1 represents a level of 1283
thermal energy that generally will not cause a burn injury. 1284
9.2.2 TS2 1285
Rationale: A TS2 thermal energy source has sufficient energy to cause a burn injury in 1286
some circumstances. The occurrence of a burn from a TS2 source will 1287
largely depend on the duration of contact. Depending on the contact time, 1288
and contact area, contact material, and other factors, a TS2 source is not 1289
likely to cause an injury requiring professional medical attention. Table 38 1290
defines the upper limits for TS2 surfaces. 1291
A TS2 circuit is an example of a class 2 energy source where the basic 1292
safeguard may, in some cases, be replaced by an instructional 1293
safeguard. Details are given in Table 38, footnote e. 1294
9.2.3 TS3 1295
Rationale: A TS3 thermal energy source has sufficient energy to cause a burn injury 1296
immediately on contact with the surface. There is no table defining the 1297
limits for a TS3 surface because any surface that is in excess of TS2 limits 1298
is considered to be TS3. Within the specified contact time, as well as 1299
contact area, contact material and other factors, a TS3 source may cause 1300
an injury requiring professional medical attention. As TS3 surfaces require 1301
that maximum level of safeguard defined in the document. All surfaces 1302
may be treated as TS3 if not otherwise classified. 1303
Source: IEC Guide 117. 1304
Rationale: When doing the temperature measurements, an ambient temperature is 1305
used as described in 9.2.5 to measure the temperatures without taking into 1306
account the maximum ambient specified by the manufacturer. 1307
9.3 Touch temperature limits 1308
Table 38 Touch temperature limits for accessible parts 1309
Source: The limits in Table 38 are primarily derived from data in IEC Guide 117. 1310
Rationale: The temperature of the skin and the duration of raised temperature are the 1311
primary parameters in the occurrence of a skin bur n injury. In practice, it is 1312
difficult to measure the temperature of the skin accurately while it is in 1313
contact with a hot surface. Thus the limits in Table 38 do not represent skin 1314
temperatures. These limits do represent the surface temperatures that are 1315
known to cause a skin burn injury when contacted for greater than the 1316
specified time limit. 1317
The thermal energy source criterion takes account of the temperature of 1318
the source, its thermal capacity and conductivity as well as the likely 1319
duration and area of contact. As the thermal capacity and conductivity will 1320
normally remain constant for a given surface, the limits here are expressed 1321
in degrees C for typical material types and contact durations. 1322
– 122 – IEC TR 62368-2:20xx © IEC 2019
Contact time duration > 8 h 1323
For devices worn on the body (in direct contact with the skin) in normal use 1324
(> 8 h), examples include portable, lightweight devices such watches, 1325
headsets, music players and sports monitoring equipment. Since the 1326
values in the table do not represent skin temperature as indicated above, 1327
measurements should not be done while wearing the devices . 1328
The value of 43 °C for all materials for a contact period of 8 h and longer 1329
assumes that only a minor part of the body (less than 10 % of the entire 1330
skin surface of the body) or a minor part of the head (less than 10 % of the 1331
skin surface of the head) touches the hot surface. If the touching area is 1332
not local or if the hot surface is touched by vital areas of the face ( for 1333
example, the airways), severe injuries may occur even if the surface 1334
temperature does not exceed 43 °C (see IEC Guide 117). 1335
NOTE Prolonged exposure to 43 °C may result in erythema (temporary redness of the skin 1336 causing dilation of the blood capillaries) which will typically go away within a few hours after 1337 removal of the heat source. For some users, this may be mis perceived as a burn. 1338
Contact time durations > 1 min 1339
For very long-term contact ( 10 min), the temperature below which a burn 1340
will not occur converges towards 43 °C for most materials (see 1341
IEC Guide 117:2010, Figure A.1). Studies carried out on portable IT 1342
Equipment have shown that for long term contact, a surface temperature 1343
will drop by between 5 °C and 12 °C when in contact with the body due to 1344
the cooling effect of the blood circulation. On this basis, and taking ac count 1345
of the probability that long-term contact will normally be insulated by 1346
clothing or some other form of insulation, the TS1 temperature limit for 1347
contact periods greater than 1 min in Table 39 are conservatively chosen 1348
as 48 °C for all materials. 1349
Examples of products with surfaces where expected continuous contact 1350
durations greater than 1 min include joysticks, mice, mobile telephones, 1351
and PDAs. Any handles, knobs or grips on the equipment that are likely, 1352
under normal usage, to be touched or held for greater than 1 min are also 1353
included. 1354
Contact time durations between 10 s and 1 min 1355
For surfaces that are touched for shorter contact durations (up to 1 min), 1356
the temperature below which a burn will not occur is influenced by the 1357
material type as well as other factors. Because the contact time is shorter, 1358
there is insufficient time for heat transfer to cause the cooling effect 1359
described above, so it is not considered in the limits. The TS1 temperature 1360
limits in Table 38 for contact durations up to 1 min are taken directly from 1361
IEC Guide 117:2010, Table A.1. 1362
Examples of surfaces with contact durations up to 1 min include handles or 1363
grips used primarily for moving or adjusting the equipment. Also tuning 1364
dials or other controls where contact for up to 1 min may be expected. 1365
Contact time durations up to 10 s 1366
Even shorter-term contact may occur for surfaces such as push 1367
button/switch, volume control; computer or telephone keys. In this case, 1368
the surfaces will not normally be touched for a duration greater than 10 s. 1369
The TS1 temperature limits in Table 38 for these surfaces are based on the 1370
burn threshold limits in IEC Guide 117 for contact durations of up to 10 s. 1371
IEC TR 62368-2:20xx © IEC 2019 – 123 –
For surfaces that are accessible but need not be touched to operate the 1372
equipment, contact duration of up to 1 s is assumed. For healthy adults, a 1373
minimum reaction time of 0,5 s can be assumed. For more general 1374
applications, the reaction time increases to 1 s IEC Guide 117, Table 2. 1375
The TS1 temperature limits in Table 38 for these surfaces are based on the 1376
burn threshold limits in Guide 117 for contact durations of 1 s 1377
(see IEC Guide 117:2010, Figures A.1 – A.6). More conservative values 1378
than those in IEC Guide 117 are chosen for metal and glass to provide 1379
some margin against a reduced reaction time while in contact with a high 1380
thermal energy surface of high thermal conductivity. 1381
Examples of such parts include general enclosure surfaces, accessible 1382
print heads of dot matrix printers or any internal surfaces that may be 1383
accessible during routine maintenance. Accidental contact, with no 1384
intention to hold or contact the surface is also included. 1385
For contact durations between 1 s and 10 s, IEC Guide 117 provides 1386
temperature ranges over which a burn may occur rather than precise limits. 1387
This takes account of the uncertainty that applies to the occurrence of b urn 1388
injury over shorter periods. The texture of the surface can also be a factor 1389
in the occurrence of a burn and this is not taken into account in the limits in 1390
IEC Guide 117. As most surfaces in IT equipment will have some texturing, 1391
values at the higher end of the spreads have been chosen. 1392
Contact time durations up to 1 s 1393
For accessible surfaces that are not normally intended or expected to be 1394
touched while operating or disconnecting the equipment, a contact time 1395
duration of up to 1 second is appropriate. This would apply to any surface 1396
of the equipment that does not have functionality when touched or is 1397
unlikely to be inadvertently contacted when accessing functional surfaces 1398
such as keyboards or handles. Typical and readily expected usage should 1399
be considered when assessing likely contact duration with such a surface. 1400
For example, it is not necessary to touch a direct plug -in external power 1401
supply adapter (Figure x) during normal use of the equipment , but it will 1402
likely be touched or briefly held for disconnection from the mains. Thus, 1403
this type of equipment is expected to be contacted for more than one 1404
second. 1405
1406
1407
1408
1409
1410
1411
Figure x Figure y 1412
Other external power supplies, such as those often supplied with notebook 1413
computers and other equipment (Figure y) , with a connected power cord 1414
will not normally be touched either during usage or for disconnection. For 1415
external power supplies with power cord, to disconnect from mains, the 1416
user will grip the power cord plug. The contact time with the plug would be 1417
more than 1 second and the contact time of the po wer supply would be less 1418
than 1 second. 1419
Met opmerkingen [RJ6]: See Raleigh minutes item 7.1.3
– 124 – IEC TR 62368-2:20xx © IEC 2019
Other considerations 1420
In the event of a fault condition arising, the user is less likely to touch the 1421
equipment and any contact with accessible surfaces is likely to be very 1422
brief. Thus higher limits than those allow ed under IEC Guide 117 are 1423
permitted. For metal, glass and plastic surfaces, the limit is 100 °C 1424
(IEC 60065:2010, Table 3). For wood, a temperature of 150 °C was chosen 1425
because 100 °C would be lower than the normal temperature of 140 °C. 1426
When contact with a TS1 surface is unlikely due to its limited size or 1427
accessibility, a temperature up to 100 °C is acceptable if an instructional 1428
safeguard is provided on the equipment (see IEC 60950-1:2005, Table 4C, 1429
IEC 60065:2001, Table 3). 1430
In the case where a surface is hot in order to carry out its function, the 1431
occurrence of contact with the surface or a subsequent burn injury is 1432
unlikely if the user is made aware that the surface is hot. Thus, a 1433
temperature up to 100 °C or higher is acceptable if there is an effec tive 1434
instructional safeguard on the body of the equipment indicating that the 1435
surface is hot (see IEC 60950-1:2005, Table 4C and IEC 60065:2001, 1436
Table 3). 1437
Factors for consideration in determining test conditions 1438
For consistency with other parts of the document and to reflect typical user 1439
conditions, the ambient conditions described in B.1. 6 apply. 1440
Assessment of safeguards should be carried out under normal operating 1441
conditions of the product that will result in elevated surface temperatures. 1442
The chosen normal operating conditions should be typical of the 1443
manufacturer’s intended use of the product while precluding deliberate 1444
misuse or unauthorized modifications to the product or its operating 1445
parameters by the user. For some simple equipment, this will be 1446
straightforward. For more complex equipment, there may be several 1447
variables to be considered including the typical usage model. The 1448
manufacturer of the equipment should perform an assessment to determine 1449
the appropriate configuration. 1450
Example: Factors that may be considered in determining the test conditions 1451
for a notebook computer: 1452
– Mode of operation 1453
• Variable CPU speed 1454
• LCD brightness 1455
– Accessories installed: 1456
• Number of disk drives 1457
• USB devices 1458
• External HDD 1459
– Software installed: 1460
• Gaming applications 1461
• Duration of continuous use 1462
• Long term contact likely? 1463
• Other specialist applications 1464
– Battery status: 1465
• Fully charged/ Discharged 1466
• AC connected 1467
IEC TR 62368-2:20xx © IEC 2019 – 125 –
9.3.1 Touch temperature limit requirements 1468
Rationale: Table 38 provides touch temperature limits for accessible parts, assuming 1469
steady state. IEC Guide 117 provides the methodology to assess products 1470
with changing temperatures or small parts which are likely to drop in 1471
temperature upon touch. Using a thermesthesiometer for a specified time 1472
interval, the thermesthesiometer simulates the skin temperature of human 1473
finger and heating effects caused by contact with the product surface under 1474
test. Once contact is made, the thermesthesiometer and product under test 1475
will eventually reach thermal equilibrium at which point finger skin 1476
temperature can be determined. 1477
Background: The touch limits from Table 38 for > 1 s and < 10 s may be used for small 1478
hand-held devices with localized hotspots, given a small thermal energy 1479
source and touching can be easily avoided by changing holding posit ion of 1480
the device. 1481
This same rationale would also apply to small multi -media peripherals 1482
which are removed from a host device ( for example, USB memory stick, 1483
PCMCIA cards, SD card, Compact Flash card, ejectable media, etc.). In 1484
many cases, these peripherals may be removed from their host ( for 1485
example, power source) exposing higher thermally conductive materials 1486
(for example, metals), but are in thermal decay (i.e. no longer powered). 1487
In cases of doubt, the method in IEC Guide 117 may be used for steady-1488
state conditions. An example of a simplified method for thermally decaying 1489
parts is provided as a reference: 1490
Touch temperature limits in IEC Guide 117 are based on time-weighted 1491
exposure for burn (for example, thermal energy). As long as integrated 1492
thermal energy calculations (for example, area of temp vs. time) of the part 1493
at specified time intervals is less than the associated integrated thermal 1494
energy calculated limits over that duration, the measured temperatures 1495
should be acceptable. 1496
The most significant time internals to consider for decaying thermal energy 1497
is between 1 s to 10 min (using 10 s, 1 min, 10 min intervals). 1498
– For exposure times < 1 s, the 1 s temperature limits of the 1499
IEC Guide 117 should be used for 2 reasons: 1) Reaction times – 1500
under general applications reaction times of < 1 s are not probable and 1501
greatest risk of burn. 2) Repeatability – temperature measurement 1502
capability < 1 s intervals is less common and more difficult to accurately 1503
calculate the part energy. 1504
– For exposure times > 10 min, the temperature limits of IEC Guide 117 1505
should be used: after 10 min parts should either have cooled or reach 1506
sufficient equilibrium to utilize the temperature limits without the need 1507
for assessing thermal energy. 1508
This simplified method requires the part under test to be mounted using 1509
thermally insulating clamp. Clamp to the part’s least thermally conductive 1510
material and smallest contact needed to hold the part. Measured in still -air 1511
room ambient. 1512
NOTE Parts that are hand-held will decay faster than open-air measurements (for example, 1513 radiation and convection) owing to direct conduction of heat to skin. 1514
9.3.2 Test method and compliance criteria 1515
Rationale: The general intent of the requirements are to use an ambient temperature 1516
as follows without taking into account the maximum ambient specified by 1517
the manufacturer: 1518
– The test may be performed between 20 °C and 30 °C. 1519
– If the test is performed below 25 °C, the results are normalized to 1520
25 °C. 1521
– 126 – IEC TR 62368-2:20xx © IEC 2019
– If the test is performed above 25 °C, the results are not normalized to 1522
25 °C and the limits (Table 38) are not adjusted. In case the product 1523
fails the requirements, the test may be repeated at 25 °C. 1524
9.4 Safeguards against thermal energy sources 1525
Rationale: TS1 represents non-hazardous energy and thus, no safeguard is required. 1526
Because the energy is non-hazardous, and there is no possibility of an 1527
injury, it may be accessible by ordinary persons and there is no 1528
restriction on duration of contact under normal operating conditions. 1529
TS2 represents hazardous energy that could cause a burn injury if the 1530
contact duration is sufficient. Therefore, a safeguard is required to protect 1531
an ordinary person. A TS2 surface will not cause a burn immediately on 1532
contact. Because the burn injury from a TS2 surface is likely to be minor 1533
and pain or discomfort is likely to precede the occurrence of a burn injury, 1534
a physical safeguard may not be required if there is an effective means to 1535
inform the ordinary person about the risks of touching the hot surface. 1536
Thus, a TS2 safeguard may be one of the following: 1537
– a physical barrier to prevent access; or 1538
– an instructional safeguard to limit contact time below the threshold 1539
limit value versus time. 1540
TS3 represents hazardous energy that is li kely to cause a burn injury 1541
immediately on contact. Because a TS3 surface is always likely to cause a 1542
burn immediately or before the expected reaction time due to pain or 1543
discomfort, an equipment safeguard is required. 1544
Unless otherwise specified in the document, ordinary persons need to be 1545
protected against all TS2 and TS3 energy sources. 1546
Instructed persons are protected by the supervision of a skilled person 1547
and can effectively employ instructional safeguards. Thus, equipment 1548
safeguards are not required for TS2 energy sources. An instructional 1549
safeguard may be required. 1550
TS3 energy sources can cause severe burns after very short contact 1551
duration. Thus, an instructional safeguard alone is not sufficient to 1552
protect an instructed person and an equipment safeguard is required. 1553
Skilled persons are protected by their education and experience and are 1554
capable of avoiding injury from TS3 sources. Thus, an equipment 1555
safeguard is not required to protect against TS3 energy sources. As a pain 1556
response may cause an unintentional reflex action even in skilled 1557
persons, an equipment or instructional safeguard may be required to 1558
protect against other class 3 energy sources adjacent to the TS3 energy 1559
source. 1560
9.5.1 Equipment safeguard 1561
Rationale: The function of the equipment safeguard is to limit the transfer of 1562
hazardous thermal energy. An equipment safeguard may be thermal 1563
insulation or other physical barrier. 1564
9.5.2 Instructional safeguard 1565
Rationale: An instructional safeguard will inform any person of the presence of 1566
hazardous thermal energy. Instructional safeguards may be in a text or 1567
graphical format and may be placed on the product or in the user 1568
documentation. In determining the format and location of the safeguard, 1569
consideration will be given to the expected user group, the likelihood of 1570
contact and the likely nature of the injury arising. 1571
IEC TR 62368-2:20xx © IEC 2019 – 127 –
9.6 Requirements for wireless power transmitters 1572
Rationale: Transmitters for near-field wireless power transfer can warm up foreign 1573
metallic objects that may be placed close to or on s uch a transmitter. To 1574
avoid burn due to high temperatures of the foreign metallic objects, the 1575
transmitter is tested as specified in 9.6.3. 1576
Far-field transmitters are generally called "power-beaming" and are not 1577
covered by these requirements. 1578
9.6.3 Test method and compliance criteria 1579
Rationale: While 9.6.3 specifies a maximum temperature of 70 °C, aluminum foil that 1580
reaches 80 °C is considered to comply with the requirement. The foil 1581
described in figure 49 complies with the method allowed in in 9.3.1 based 1582
on the foil dimensions and low mass. 1583
This requirement is expected to align with the current Qi standard. 1584
Rationale: While many devices (servers, laptops, etc.) may be evaluated accurately 1585
for thermal burn injury using Table 38, foreign objects (FO’s) and other 1586
similar devices with low thermal mass and finite heat flux cannot be 1587
evaluated for thermal burn injury accurately. 1588
Both the experimental (thermesthesiometer method) and the computational 1589
(bio-heat equation model) in conjunction with the thermal burn thresholds 1590
from ASTM C 1055 provide for a greater level of accuracy than IEC Guide 1591
117 in assessing the potential risk for thermal burn injury from foreign 1592
objects by, 1593
- representing temperatures of the skin; 1594
- being material and geometry agnostic and; 1595
- considering quality of contact. 1596
Both methods take into account conservative assumptions th at build in a 1597
margin of safety: 1598
- single finger (typically, finger and thumb would be used to pick up 1599
object); 1600
- no perfusion; 1601
- children/elderly reaction times; and 1602
- full thickness burn thresholds (vs +10˚C to obtain TS2). 1603
However, the findings from the experimental thermesthesiometer testing 1604
are being recommended due to the simplicity of the test method and to 1605
further promote future hazard-based testing using the thermesthesiometer. 1606
____________ 1607
10 Radiation 1608
10.2 Radiation energy source classifications 1609
Rationale: The first step in application is determining which energy sources repre sent 1610
potential radiation energy sources. Each energy source within the product 1611
can be classified as a radiation source based on the available energy 1612
within a circuit that can be used to determine the type of and number of 1613
safeguards required. The radiation energy source classifications include 1614
electromagnetic radiation energy sources. 1615
Met opmerkingen [JR7]: See Shanghai minutes item 6.1.10
– 128 – IEC TR 62368-2:20xx © IEC 2019
10.2.1 General classification 1616
Rationale: Radiation energy source classifications for X -rays and acoustics are given in 1617
Table 39. For optical radiation (“Lasers” and “Lamps and lamp systems”), the 1618
classification is defined by the IEC 60825 series or the IEC 62471 series as 1619
applicable. 1620
The general classification scheme specified in IEC 60825-1 is for laser 1621
products and is not a classification scheme for energy sources. It is no t 1622
practical to classify laser radiation as RS. The classification according to 1623
IEC 60825-1 is used without modification. 1624
The classification schemes given in IEC 62471 and IEC 62471-5 specify a 1625
measurement distance (200 mm other than lamps intended for gen eral lighting 1626
service and 1m for Image projectors) for the determination of the Risk Group. 1627
The Risk Group classification is not the actual source of the light. It is not 1628
practical to classify the radiation from lamps and lamp systems as RS. The 1629
classification according to IEC 62471 is used without modification. 1630
Abnormal operating conditions (see Clause B.3) and single fault 1631
conditions (see Clause B.4) need to be taken into account. If it becomes 1632
higher risk group when abnormal operating condition or single fault 1633
condition is applied, the higher risk group is applied for classification. 1634
Laser equipment classified as Class 1C is generally not within the scope of this 1635
document as it mainly applies to medical related applications. 1636
1637
IEC TR 62368-2:20xx © IEC 2019 – 129 –
Source: IEC 60825-1:2014 and IEC 62471-5 1638
Rationale: Image Projectors are evaluated using the process in Figure 43 in this 1639
document (see IEC 60825-1:2014 and IEC 62471-5). 1640
1641
Figure 43 – Flowchart for evaluation of Image pro jectors (beamers) 1642
10.2.2 & 10.2.3 RS1 and RS2 1643
Rationale: The output circuits of personal music players are not subject to single 1644
fault conditions, since the outputs will not increase to a level exceeding 1645
RS2 by nature of their highly integrated hardware de signs. Typically, when 1646
component faults are introduced during testing (by bypassing or shorting of 1647
the audio related ICs), the outputs are either shut down, reduced in level or 1648
muted. 1649
– 130 – IEC TR 62368-2:20xx © IEC 2019
10.2.4 RS3 1650
Rationale: RS3 energy sources are those that are not otherwis e classified as RS1 or 1651
RS2. No classification testing is required as these energy sources can 1652
have unlimited levels. If an energy source is not measured, it assumed to 1653
be RS3 for application of the document. A skilled person uses personal 1654
protective equipment or measures to reduce the exposure to safe limits 1655
when working where RS3 may be present. 1656
10.3 Safeguards against laser radiation 1657
Source: IEC 60825-1:2014, Annex A 1658
Rationale: IEC 60825-1:2014, Annex A provides an explanation of the different 1659
classes of products. Accessible emission limits (AELs) are generally 1660
derived from the maximum permissible exposures (MPEs). MPEs have 1661
been included in this informative annex to provide manufacturers with 1662
additional information that can assist in evaluating the safet y aspects 1663
related to the intended use of their product , such as the determination of 1664
the nominal ocular hazard distance (NOHD). 1665
10.4 Safeguards against optical radiation from lamps and lamp systems (including 1666
LED types) 1667
Source: IEC 62471 and IEC TR 62471-2 1668
Rationale: Excessive optical radiation may damage the retina and cause vision 1669
impairment or blindness. The limits in the referenced documents are 1670
designed to reduce the likelihood of vision impairment due to optical 1671
radiation sources. 1672
For the Instructional safeguard for lamps and lamp systems, see IEC 1673
TR 62471-2. 1674
10.4.1 General Requirements 1675
Source: IEC 60065 1676
Rationale: The term ‘Electronic light effect equipment ’ has been used in IEC 60065 1677
(see 1.1) and is a commonly understood term for entertainment/sta ge 1678
effect lighting. 1679
10.5 Safeguards against X-radiation 1680
Source: IEC 60950-1; IEC 60065 1681
Rationale: Exposure to X-radiation will cause injury with excessive exposure over 1682
time. The limits in this document have been selected from IEC 60950-1 and 1683
IEC 60065 in order to limit exposure to that which is below harmful levels. 1684
10.6 Safeguards against acoustic energy sources 1685
Source: EN 60065:2002/A11:2008 1686
Rationale: The requirements of this subclause are made to protect against hearing 1687
loss due to long term exposure to high sound pressure levels. Therefore, 1688
the requirements are currently restricted to those kind s of products that are 1689
designed to be body-worn (of a size suitable to be carried in a clothing 1690
pocket) such that a user can take it with them all day long to l isten to music 1691
(for example, on a street, in a subway, at an airport, etc.) . 1692
At this moment, the clause does not contain requirements against the 1693
hazard of short term exposure to very high sound pressure levels. 1694
Rationale: Significance of LAeq,T in EN 50332-1 and additional information 1695
LAeq,T is derived from the general formula for equivalent sound pressure: 1696
IEC TR 62368-2:20xx © IEC 2019 – 131 –
1697
This can be represented graphically as given in Figure 44 in this document. 1698
1699
Figure 44 – Graphical representation of LAeq,T 1700
In EN 50332-1 the measurement time interval (t2 – t1) is 30 s. 1701
In practice, and for the purposes of listening to personal music player 1702
content, LAeq,T has a time interval T (t2 – t1) in the order of minutes / hours 1703
and not seconds. 1704
Subclause 6.5 (Limitation value) of EN 50332-1:2000 acknowledges this 1705
fact and states that the 100-dB limit equates to a long time average of 90 1706
dB LAeq,T. By using the IEC 60268-1 “programme simulation noise” test 1707
signal, this also takes the spectral content into account. 1708
The SCENHIR report states that 80 dB(A) is considered safe for an 1709
exposure time of 40 h/week. Most persons do not listen to 40 h/week to 1710
their personal music player. In addition, not all music tracks are at the 1711
same level of the simulated noise signal. Whilst modern music tends to be 1712
at around the same level, most of the available music is at a lower average 1713
level. Therefore, CLC TC 108/WG03 considered a value of 85 dB(A) to be 1714
safe for an overwhelming majority of the users o f personal music players. 1715
10.6.3 Requirements for dose-based systems 1716
Rationale: The requirements on dose measurement have been developed to replace 1717
the requirements on maximum exposure as this better protects against 1718
hearing damage, which results from the combination of exposure and time 1719
(dose). For now, both systems can be used. See Table 16 in this document 1720
for a comparison. 1721
– 132 – IEC TR 62368-2:20xx © IEC 2019
The dose-based system mainly uses the expression CSD, meaning 1722
"calculated sound dose". The value is based on the values mentioned in 1723
the EU Commission Decision 2009/490/EC, which stipulated that sound is 1724
safe when below 80 dB(A) for a maximum of 40 h per week. Therefore, the 1725
value of 100 % CSD corresponds to 80 dB(A) for 40 h. This also means 1726
that the safe limit in the dose measurement system is chosen to be lower 1727
than the safe limit in the maximum exposure system, as this specifies the 1728
safe limit at 85 dB(A). Consequently, a user will normally receive warnings 1729
earlier with the dose measurement system compared to the maximum 1730
exposure limit. In the maximum exposure system, the warning only had to 1731
be given once every 20 h of listening when exceeding 85 dB(A). In the 1732
dose measurement system, the warning and acknowledgement has to be 1733
repeated at least at every 100 % increase of the dose. In practice, this 1734
means that the warning is repeated at a comparable level of 83 dB(A), 1735
meaning a dose that corresponds to listening to 83 dB(A) for 40 h. At each 1736
next 100 % increase of dose level, the increase in correspon ding dB’s is 1737
halved. Manufacturers have the freedom to give warnings earlier or ask for 1738
acknowledgement more frequently, but it has to be no later than at the next 1739
100 % CSD increase since the last acknowledgement. For example, a 1740
device has provided the warning and acknowledgement at 100 % CSD. The 1741
manufacturer may choose to provide the next warning before 200 % CSD, 1742
for example, at 175 % CSD. If that is done, the next warning and 1743
acknowledgement may not be later than at 1744
275 % CSD. While there are no requi rements for manufacturers to warn 1745
users before the 100 % CSD is reached, it is allowed to do so. Even more, 1746
it was felt by the document writers that it would be responsible behaviour if 1747
manufacturers warn consumers about the risks before the 100 % CSD leve l 1748
is reached. With the maximum exposure measurement, the maximum 1749
allowable sound output is 100 dB(A). With the dosage system, only a 1750
momentary exposure limit (MEL) is required when exceeding 100 dB(A) if a 1751
visual or audible warning is provided. Where a vis ual or audible MEL is not 1752
provided the maximum exposure measurement of 100 dB(A) is required. 1753
An essential element to educating the user and promoting safe listening 1754
habits is appropriate and useful guidance. This can be accomplished with 1755
informative CSD and MEL warnings that allow the user to understand the 1756
hazard, risks, and recommended action. Appropriate warnings about using 1757
the device and user instructions shall be provided. It should be noted that 1758
the CSD warning can be provided in various forms not limited to visual or 1759
audio. However, the MEL can only be provided visually or audibly. 1760
Consideration should be given to not over-message and annoy the user to 1761
the point where the message is neglected or evasive attempts (software 1762
hacks) to defeat the safe guards are taken. Extreme care should be given 1763
when implementing the MEL warning and shall be at the discretion of the 1764
manufacturer. 1765
Manufacturers should be aware that digital sensitivity between PMP and 1766
unknown listening devices may result in excessive f alse positives. It is 1767
recommended industry to promote sharing of sensitivity data through a 1768
standardized means. 1769
IEC TR 62368-2:20xx © IEC 2019 – 133 –
Table 16 – Overview of requirements for dose-based systems 1770
Devices with Visual or Audible MEL EN 50332-3
SPL
before transition3
SPL
after transition3
Dose
requirements
Dose
test method
Analog known 1
> 85 dB(A) if ack,
< 100 dB(A) max
<80 dB(A) max
CSD warn at every 100 %
MEL warn at >100 dB(A)
cl 5.2
Analog unknown 2
> 27 mV r.m.s. if ack,
< 150 mV r.m.s. max
< 15 mV rms max
CSD warn at every 100 % (= integrate. rms level 15 mV)
MEL warn at > 150 mV r .m.s.
cl 5.3
Digital known 1
> 85 dB(A) if ack,
< 100 dB(A) max
< 80 dB(A) max
CSD warn at every 100 %
MEL warn at > 100 dB(A)
cl 5.2
Digital unknown 2
> -25 dBFS if ack,
< 100 dB(A)4 max
< -30 dBFS max
CSD warn at every 100 % (= integrate level -30 dBFS)
< 100 dB(A) max or MEL warn at > 100 dB(A)4
TBD 5
Devices without MEL EN 50332-3
SPL
before transition3
SPL
after transition3
Dose
requirements
Dose
test method
Analog known 1
> 85 dB(A) if ack,
< 100 dB(A) max
< 80 dB(A) max
CSD warn at every 100 %
< 100 dB(A) max
cl 5.2
Analog unknown 2
> 27 mV r.m.s. if ack,
< 150 mV r.m.s. max
< 15 mV r.m.s. max
CSD warn at every 100 % (= integrate rms level 15 mV)
< 150 mV r.m.s. max
cl 5.3
Digital known 1
> 85 dB(A) if ack,
< 100 dB(A) max
< 80 dB(A) max
CSD warn at every 100 %
< 100 dB(A) max
cl. 5.2
Digital unknown 2
> -25 dBFS if ack,
< 100 dB(A)4 max
< -30 dBFS max
CSD warn at every 100 % (= integrate level -30 dBFS)
< 100 dB(A)4 max
TBD 5
1 PMP includes or can detect listening device
2 PMP cannot detect listening device
3 Transition period allows migration to CSD before becoming mandatory
4 Defaults to 100 dB(A) gain cap from digital listening device. Need to develo p industry wide protocol for digital (wired/wireless) listening device for PMPs to learn sensitivity lookup table.
5 Need to create test requirements with EN 50332-3. Otherwise, SPL requirements (30 dBFS gain cap) will be only feasible option.
1771
– 134 – IEC TR 62368-2:20xx © IEC 2019
10.6.6.1 Corded listening devices with analogue input 1772
Rationale: The value of 94 dB(A) was chosen to align with current practice in EN 1773
50332. In addition, some equipment may already start clipping at 100 1774
dB(A). The value used does not influence the result of the me asurement. 1775
_____________ 1776
Annex A Examples of equipment within the scope of this standard 1777
Rationale: A variety of personal electronic entertainment products/systems can be 1778
covered by this document, including self-propelling types sometimes known 1779
as entertainment robots, which typically contain electronic components and 1780
circuits that power the device's motion, a battery system and charger, the 1781
electric motor(s) and control systems, together with wireless 1782
communications and audio. When no other IEC or ISO document explicitly 1783
covers these products, they can be accommodated by IEC 62368-1. 1784
Examples of Entertainment-type Robots: 1785
1786
____________ 1787
Annex B Normal operating condition tests, abnormal operating condition 1788
tests and single fault condition tests 1789
General Equipment safeguards during various operating conditions 1790
Purpose: To identify the various operating and use conditions of equipment that are 1791
taken into account in the document. This clause was proposed to be added to 1792
the document as a Clause 0.12, but was agreed to be added to the Rationale 1793
instead. 1794
Rationale: Operating conditions 1795
Normal operating condition – A normal operating condition is a state with 1796
intended functionality of the equipment. All equipment basic safeguards, 1797
supplementary safeguards, and reinforced safeguards remain effective and 1798
comply with all required safeguard parameters. 1799
IEC TR 62368-2:20xx © IEC 2019 – 135 –
Abnormal operating condition – An abnormal operating condition is a 1800
temporary state. The equipment may have full, limited, or no functionality. The 1801
equipment generally requires operator intervention for restoration to normal 1802
operating condition. All equipment basic safeguards remain effective but 1803
may not need to comply with the required safeguard parameters. All 1804
equipment supplementary safeguards and reinforced safeguards remain 1805
effective and comply with the required safeguard parameters. 1806
Upon restoration of normal operating conditions, all basic safeguards 1807
comply with the required parameters unless the abnormal operating 1808
condition leads to a single fault condition, in which case the requirements 1809
for single fault condition apply. 1810
Reasonably foreseeable misuse condition – Reasonably foreseeable 1811
misuse is a form of an abnormal operating condition but may be either a 1812
temporary or a permanent state. The equipment may have full, l imited, or no 1813
functionality. The equipment may not be capable of restoration to a normal 1814
operating condition . Reasonably foreseeable misuse may lead to a single 1815
fault condition, in which case equipment basic safeguards are not required 1816
to remain effective. All equipment supplementary safeguards and reinforced 1817
safeguards remain effective and comply with the required safeguard 1818
parameters. 1819
Other misuse condition – Other misuse (unreasonable or unforeseeable) may 1820
lead to a single or multiple fault condition, in which basic safeguards, 1821
supplementary safeguards and reinforced safeguards may not remain 1822
effective. The equipment may not be repairable to a normal operating 1823
condition. Safeguards against unreasonable or unforeseeable misuse are not 1824
covered by this document. 1825
Single fault condition – A single fault condition is a component or 1826
safeguard fault. The equipment may have full, limited or no functionality. The 1827
equipment requires repair to return to a normal operating condition . 1828
Equipment basic safeguards are not required to be functional, in this case the 1829
supplementary safeguards are functional and comply with the required 1830
safeguard parameters; or equipment supplementary safeguards are not 1831
required to be functional, in this case the basic safeguards are functional and 1832
comply with the required safeguard parameters. 1833
NOTE As a basic safeguard and a supplementary safeguard may be interchangeable, the 1834 concept of which safeguard is not required to remain effective can be reversed. 1835
B.1.5 Temperature measurement conditions 1836
Source: IEC 60950-1 1837
Purpose: To determine whether the steady state temperature of a part or material does 1838
or does not exceed the temperature limit for that part or material. 1839
Rationale: Steady state is considered to exist if the temperature rise does not exceed 1840
3 K in 30 min. If the measured temperature is less than the required 1841
temperature limit minus 10 %, steady state is considered to exist if the 1842
temperature rise does not exceed 1 K in 5 min. 1843
Temperature rise follows an exponential curve and asymptotically approaches 1844
thermal equilibrium. The rate of temperature rise can be plotted as a function of 1845
time and used to guess the value at steady state. The actual steady state value 1846
needs to be accurate only to the extent to prove whether the value will exceed 1847
the limit or not. 1848
Steady-state conditions of typical electronic devices have many different 1849
temperatures, so thermal equilibrium does not exist. 1850
– 136 – IEC TR 62368-2:20xx © IEC 2019
The resistance method may be used to measure temperature rises of windings 1851
unless the windings are non-uniform or if it is difficult to make the necessary 1852
connections, in which case the temperature rise is determined by other means. 1853
When the resistance method is used, t he temperature rise of a winding is 1854
calculated from the formula: 1855
Δt = 1
12
R
RR − (k + t1) – (t2 – t1) 1856
where: 1857
Δt is the temperature rise of the winding; 1858
R1 is the resistance at the beginning of the test; 1859
R2 is the resistance at the end of the test; 1860
k is equal to: 1861
• 225 for aluminium windings and copper/aluminium windings with an 1862
aluminium content ≥ 85 %, 1863
• 229,75 for copper/aluminium windings wi th a copper content 15 % 1864
to 85 %, 1865
• 234,5 for copper windings and copper/aluminium windings with an 1866
copper content ≥ 85 %; 1867
t1 is the room temperature at the beginning of the test; 1868
t2 is the room temperature at the end of the test. 1869
NOTE It is recommended that the resistance of windings at the end of the test be determined by 1870 taking resistance measurements as soon as possible after switching off and then at short 1871 intervals so that a curve of resistance against time can be plotted for ascertaining the resist ance 1872 at the instant of switching off. 1873
B.2.3 Supply Voltage 1874
Rationale: Where a test subclause does not require the most unfavourable supply voltage, 1875
the supply voltage is the value of the rated voltage or any value in the rated 1876
voltage range. This is applicable to the tests in abnormal operation 1877
condition and single fault condition as well. 1878
B.2 – B.3 – B.4 Operating modes 1879
See Figure 45 in this document for an overview of operating modes. 1880
1881
Figure 45 – Overview of operating modes 1882
IEC TR 62368-2:20xx © IEC 2019 – 137 –
B.4.4 Functional insulation 1883
Rationale: The use of a functional insulation is only acceptable when the circuit does 1884
not exceed its limits of its class under normal operating conditions and 1885
abnormal operation conditions and single fault conditions of a component 1886
not serving as a safeguard (see 5.2.1.1 and 5.2.1.2). Otherwise a basic 1887
insulation/safeguard would be required. 1888
If the functional insulation possesses a certain quality (clearance, creepage 1889
distances, electric strength) comparable to a basic safeguard, it is acceptable 1890
to omit short-circuit. 1891
This cannot be compared to the short -circuiting of a basic safeguard as 1892
required in B.4.1, because this basic safeguard is a required one, while the 1893
added quality of the functional insulation is not required. 1894
If the short-circuiting of this functional insulation with added quality would 1895
lead to a changing of the class, the functional insulation was wrongly chosen, 1896
and a basic safeguard would have been required. 1897
B.4.8 Compliance criteria during and after single fault conditions 1898
Source: IEC 60065 1899
Rationale: During single fault conditions , short term power is delivered in components 1900
which might be outside the specifications for that component. As a result, the 1901
component might interrupt. During the interruption, sometimes a small flame 1902
escapes for a short period of time. The current practice in IEC 60065 allows 1903
these short term flames for a maximum period of 10 s. This method has been 1904
successfully used for products in the scope of this document for many years. 1905
____________ 1906
Annex C UV Radiation 1907
C.1.1 General 1908
Rationale: UV radiation can affect the physical properties of thermoplastic materials and 1909
so it can have a consequential effect on components protecting body parts 1910
from a range of injurious energy sources. 1911
____________ 1912
Annex D Test generators 1913
Source: ITU-T Recommendation K.44 1914
Rationale: The circuit 1 surge in Table D.1 is typical of voltages induced into telephone 1915
wires and coaxial cables in long outdoor cable runs due to lightning strik es to 1916
their earthing shield. 1917
The circuit 2 surge is typical of earth potential rises due to either lightning 1918
strikes to power lines or power line faults . 1919
The circuit 3 surge is typical of voltages induced into antenna system wiring 1920
due to nearby lightning strikes to earth. 1921
Figure D.3 provides a circuit diagram for high energy impulse to test the high-1922
pressure lamps. 1923
____________ 1924
– 138 – IEC TR 62368-2:20xx © IEC 2019
Annex E Test conditions for equipment containing audio amplifiers 1925
Source: IEC 60065:2011 1926
Rationale The proposed limits for touch voltages at terminals involving audio signals that 1927
may be contacted by persons have been extracted without deviation from 1928
IEC 60065:2011, 9.1.1.2 a). Under single fault conditions, 11.1 of 1929
IEC 60065:2011 does not permit an increase in acceptable touch volt age limits. 1930
The proposed limits are quantitatively larger than the accepted limits of 1931
Table 4, but are not considered dangerous for the following reasons: 1932
– the output is measured with the load disconnected ( worst-case load); 1933
– defining the contact area of connectors and wiring is very difficult due to 1934
complex shapes. The area of contact is considered small due to the 1935
construction of the connectors ; 1936
– normally, it is recommended to the user, in the instruction manual provided 1937
with the equipment, that all connections be made with the equipment in the 1938
“off” condition. 1939
– in addition to being on, the equipment would have to be playing some 1940
program at a high output with the load disconnected to achieve the 1941
proposed limits. Although possible, it is highly unlikely. Historically, no 1942
known cases of injury have been recorded for amplifiers with a non-clipped 1943
output less than 71 V RMS. 1944
– the National Electrical Code (USA) permits accessible terminals with a 1945
maximum output voltage of 120 V RMS. 1946
It seems that the current normal condition specified in IEC 60065 is appropriate 1947
and a load of 1/8 of the non-clipped output power should be applied to the 1948
multichannel by adjusting the individual channels. 1949
___________ 1950
Annex F Equipment markings, instructions, and instructional safeguards 1951
F.3 Equipment markings 1952
Source: EC Directives such as 98/37/EC Machinery Directive, Annex I clause 1.7.3 1953
marking; NFPA 79:2002, clause 17.4 nameplate data; CSA C22.1 Canadian 1954
Electric Code, clause 2-100 marking of equipment give organized 1955
requirements. The requirements here are principally taken from IEC 60065 and 1956
IEC 60950 series. 1957
F.3.3.2 Equipment without direct connection to mains 1958
Source: IEC 60950-1 1959
Purpose: To clarify that equipment powered by mains circuits, but not directly connected 1960
to the mains using standard plugs and connectors, need not have an electrical 1961
rating. 1962
Rationale: Only equipment that is directly connected to the mains supplied from the 1963
building installation needs to have an electrical rating that takes into account 1964
the full load that may be connected to the building supply outlet. For equipment 1965
that is daisy-chained or involves a master-slave configuration, only the master 1966
unit or the first unit in the daisy chain needs to be marked. 1967
IEC TR 62368-2:20xx © IEC 2019 – 139 –
F.3.6.2 Equipment class marking 1968
Rationale: For compliance with EMC standards and regulations, more and more class II 1969
products are equipped with a functional earth connection. The latest version of 1970
the basic safety publication IEC 61140 allows this construction. On request of 1971
IEC TC 108, IEC SC3C has developed a new symbol, which is now used in 1972
IEC 62368-1. 1973
Rationale: Equipment having a class II construction, but that is provided with a class I 1974
input connector with the internal earthing pin not connected is also considered 1975
to be a class II equipment with functional earth. The class I connector is used 1976
to provide a more robust connection means, which is considered to be a 1977
functional reason for the earth connection. 1978
F.4 Instructions 1979
Rationale: The dash requiring graphical symbols placed on the equipment and used as an 1980
instructional safeguard to be explained does not apply to symbols used for 1981
equipment classification (see F.3.6). 1982
F.5 Instructional safeguards 1983
Rationale: When a symbol is used, the triangle represents the words “Warning” or 1984
“Caution”. Therefore, when the symbol is used, there is no need to also use the 1985
words “Warning” or “Caution”. However, when only element 2 is used, the text 1986
needs to be preceded with the words. 1987
___________ 1988
Annex G Components 1989
G.1 Switches 1990
Source: IEC 61058-1 1991
Rationale: A contact should not draw an arc that will cause pitting and damage to the 1992
contacts when switching off and should not weld when switching on if located 1993
in PS2 or PS3 energy sources. A PS1 energy source is not considered to have 1994
enough energy to cause pitting and damage to the contacts. Both these actions 1995
(pitting and damage) may result in a lot of heating that may result in fire. There 1996
should be sufficient gap between the two contact points in the off position 1997
which should be equal to the reinforced clearance if the circuit is ES3 and 1998
basic clearance if the circuit is ES2 or ES1 (we may have an arcing PIS or 1999
resistive PIS in an ES1 circuit) in order to avoid shock and fire hazards. The 2000
contacts should not show wear and tear and pitting after tests simulating 2001
lifetime endurance; and overload tests and operate normally after such tests. 2002
G.2.1 Requirements 2003
Source: IEC 61810-1, for electromechanical relays controlling currents exceeding 0,2 A 2004
AC or DC, if the voltage across the open relay contacts exceeds 35 V peak AC 2005
or 24 V DC 2006
Rationale: A contact should not draw an arc that will cause pitting and damage to the 2007
contacts when switching off and should not weld when switching on if located 2008
in PS2 or PS3 energy sources. A PS1 energy source is not considered to have 2009
enough energy to cause pitting and damage to the contacts. Both these actions 2010
(pitting and damage) may result in lot of heating that may result in fire. There 2011
should be sufficient gap between the two contact points in the off position 2012
which should be equal to the reinforced clearance if the circuit is ES3 and 2013
basic clearance if the circuit is ES2 or ES1 (we may have an arcing PIS or 2014
resistive PIS in an ES1 circuit) in order to avoid shock and fire hazards. The 2015
contacts should not show wear and tear and pit ting after tests simulating 2016
lifetime endurance, and overload tests and operate normally after such tests. 2017
– 140 – IEC TR 62368-2:20xx © IEC 2019
G.3.3 PTC thermistors 2018
Source: IEC 60730-1:2006 2019
Rationale: PTC thermistor for current limitation is always connected in series with the load 2020
to be protected. 2021
In a non-tripping stage, the source voltage is shared by the load impedance 2022
and the resistance of PTC thermistor (which is close to the zero-power 2023
resistance at 25 °C). In order to define the power dissipation of the PTC 2024
thermistor in this stage, the source voltage and the load impedance are also 2025
important parameters. 2026
In a tripping stage, the PTC thermistor heats up by itself and increases the 2027
resistance value to protect the circuit. The zero-power resistance at 25 °C is no 2028
longer related to the power dissipation of PTC thermistors in this stage. The 2029
power dissipation of PTC thermistor in this stage depends on factors such as 2030
mounting condition and ambient temperature. 2031
In either stage, some parameters other than the rated zero-power resistance at 2032
an ambient temperature of 25 C are required to calculate the power 2033
dissipation of PTC thermistor . 2034
The tripping stage is more hazardous than the non-tripping stage because the 2035
temperature of the PTC thermistor in the tripping stage becomes much higher 2036
than in the non-tripping stage. 2037
Figure 46 in this document shows “Voltage-Current Characteristics”. The blue 2038
dotted lines show the constant power dissipation line. It shows that the power 2039
at the operation point, during the tripping stage, is the highest power 2040
dissipation. This point is calculable with “Ires x Umax” of IEC 60738-1:2006, 2041
3.38. 2042
(Umax = maximum voltage, Ires = residual current, measured by the PTC 2043
manufacturers.) 2044
2045
IEC TR 62368-2:20xx © IEC 2019 – 141 –
2046
Figure 46 – Voltage-current characteristics (Typical data) 2047
If the PTC is installed in a PS1 circuit, the power dissipation of the PTC will be 2048
15W or less. In this state, the PTC is not considered to be a resistive PIS, 2049
regardless of its Ires x Umax. 2050
A PTC with a size of less than 1 750 mm3 is not considered to be a resistive 2051
PIS, described in 6.3.1, 6.4.5.2 and 6.4.6. 2052
G.3.4 Overcurrent protective devices 2053
Rationale: Just like any other safety critical component, p rotective devices are not allowed 2054
to be used outside their specif ications, to guarantee safe and controlled 2055
interruption (no fire and explosion phenomena’s) during single fault 2056
conditions (short circuits and overload conditions) in the end products. This 2057
should include having a breaking capacity capable of interrupting the maximum 2058
fault current (including short -circuit current and earth fault current) that can 2059
occur. 2060
G.3.5 Safeguard components not mentioned in G.3.1 to G.3.4 2061
Rationale: Protective devices shall have adequate ratings, including breaking capacity. 2062
G.5.1 Wire insulation in wound components 2063
Source: IEC 60317 series, IEC 60950-1 2064
Purpose: Enamel winding wire is acceptable as basic insulation between external 2065
circuit at ES2 voltage level and an ES1. 2066
Rationale: ES1 becomes ES2 under single fault conditions. The enamel winding wires 2067
have been used in telecom transformers for the past 25 years to provide basic 2068
insulation between TNV and SELV. The winding wire is type tested for 2069
electric strength for basic insulation in addition to compliance with IEC 60317 2070
series of standards. Enamel is present on both input and output winding wires 2071
and therefore, the possibility of having pinholes aligned is minimized. The 2072
finished component is tested for routine test for the applicable electric 2073
strength test voltage. 2074
– 142 – IEC TR 62368-2:20xx © IEC 2019
G.5.2 Endurance test 2075
Source: IEC 60065:2011, 8.18 2076
Rationale: This test is meant to determine if insulated winding wires without additional 2077
interleaved insulation will isolate for their expected lifetime. The endurance test 2078
comprises a heat run test, a vibration tes t and a humidity test. After those 2079
tests, the component still has to be able to pass the electric strength test. 2080
G.5.2.2 Heat run test 2081
Rationale: In Table G.2, the tolerance is ± 5 °C. It is proposed that the above tolerance be 2082
the same. 2083
G.5.3 Transformers 2084
Source: IEC 61558-1, IEC 60950-1 2085
Rationale: Alternative requirements have been successfully used with products in the 2086
scope of this document for many years. 2087
G.5.3.3 Transformer overload tests 2088
G.5.3.3.2 Compliance criteria 2089
Source: IEC 61558-1, IEC 60950-1 2090
Rationale: The transformer overload test is conducted mainly to check the deterioration by 2091
thermal stress due to overload conditions, and the compliance criteria is to 2092
check whether the temperature of the windings are within the allowable limits 2093
specified in Table G.3. For that purpose, the maximum temperature of winding s 2094
is measured. 2095
However, in the actual testing condition, the winding s or other current carrying 2096
parts of the transformer under testing may pose temperature higher than the 2097
measured value due to uneven temperature, such as a w indings isolated from 2098
the mains (see third paragraph of G.5.3.3.2) , so that such spot exposed to 2099
higher temperature may have thermal damage. 2100
In order to evaluate such potential damage, electric strength test after the 2101
overload condition is considered necessary. 2102
Both of the source documents require the electric strength test after the 2103
overload test. 2104
Table G.3 Temperature limits for transformer windings and for motor windings 2105
(except for the motor running overload test) 2106
Although the document does not clearly state it, the first row should also be 2107
used in cases where no protective device is used or the component is 2108
inherently protected by impedance. 2109
For example, in the test practice of a switch mode power supply, a transformer 2110
is to be intentionally loaded to the maximum current without a protection 2111
operating. In this case, the method of protection is NOT ‘inherently ’ or 2112
‘impedance’, but other sets of limits are specified with the time of protection to 2113
operate. In reality, a switch mode transformer tested with a maximum load 2114
attempting the protection not to operate, but the limits in first row have been 2115
considered appropriate, because the thermal stress in that loading condition 2116
continues for a long time (no ending). Thus, the lowest limit should be applied. 2117
In this context, the application of the first row limit shall be chosen according to 2118
the situation of long lasting overloading rather than the type o f protection. 2119
G.5.3.4 Transformers using fully insulated winding wir e (FIW) 2120
Source: IEC 60317-56, IEC 60317-0-7 2121
IEC TR 62368-2:20xx © IEC 2019 – 143 –
Rationale: In 2012, IEC TC 55 published IEC 60317-56 and IEC 60317-0-7, Specification 2122
for Particular Types of Winding Wires – Part 0-7: General requirements – Fully 2123
insulated (FIW) zero-defect enamelled round copper wire with nominal 2124
conductor diameter of 0,040 mm to 1,600 mm. 2125
This wire is more robust enameled-coated wire used with minimal amounts of 2126
interleaved insulation. It is another step in the advancement of technology to 2127
allow manufacturers to design smaller products safely. 2128
IEC TC 96 was the first TC to incorporate the use of FIW in their safety 2129
documents for switch mode power supply units, IEC 61558-2-16. Since 2130
IEC 62368-1:2018 references in G.5.3.1 IEC 61558-1-16 as one of the 2131
acceptable documents for transformers used in switch mode power supplies, 2132
FIW already is acceptable in equipment investigated to IEC 62368-1 that use 2133
an IEC 61558-1-16 compliant transformer. 2134
FIW may not be accessible, whether it has basic insulation, double 2135
insulation or reinforced insulation. Note that this differs from other parts of 2136
the document that permit supplementary insulation and reinforced 2137
insulation to be accessible to an ordinary person. The reason is that this 2138
kind of wire is fragile and the insulation could easily b e damaged when it is 2139
accessible to an ordinary person. 2140
G.5.4 Motors 2141
Source: IEC 60950-1 2142
Rationale: Requirements have been successfully used with products in the scope of this 2143
document for many years. 2144
G.7 Mains supply cords 2145
Source: IEC 60245 (rubber insulation), IEC 60227 (PVC insulation), IEC 60364-5-54 2146
Rationale: Mains connections generally have large normal and fault energy available from 2147
the mains circuits. It is also necessary to ensure compatibility with installation 2148
requirements. 2149
Stress on mains terminal that can result in an ignition source owing to loose or 2150
broken connections shall be minimized. 2151
Terminal size and construction requirements are necessary to ensure adequate 2152
current-carrying capacity and reliable connection such that the possibilit y of 2153
ignition is reduced. 2154
Wiring flammability is necessary to reduce flame propagation potential should 2155
ignition take place. 2156
Conductor size requirements are necessary to ensure adequate current -2157
carrying capacity and reliable connection such that the poss ibility of ignition is 2158
reduced. 2159
Alternative cords to rubber and PVC are accepted to allow for PVC free 2160
alternatives to be used. At the time of development of the document, IEC TC20 2161
had no published documents available for these alternatives. However, several 2162
countries do have established requirements. Therefore, it was felt that these 2163
alternatives should be allowed. 2164
G.7.3 – G.7.5 Mains supply cord anchorage, cord entry, bend protection 2165
Source: IEC 60065:2011 and IEC 60950-1:2013 2166
Purpose: Robustness requirements for cord anchorages 2167
Rationale: The requirements for cord anchorages, cord entry, bend protection and cord 2168
replacement are primarily based on 16.5 and 16.6 of IEC 60065:2011 and 3.2.6 2169
and 3.2.7 of IEC 60950-1:2013. 2170
– 144 – IEC TR 62368-2:20xx © IEC 2019
Experience shows that 2 mm displacement is the requirement and if an 2171
appropriate strain relief is used there is no damage to the cord and therefore, 2172
no need to conduct an electric strength test in most cases. This method has 2173
been successfully used for products in the scope of these documents for many 2174
years. 2175
G.8 Varistors 2176
Source: IEC 61051-1 and IEC 61051-2 2177
Rationale: The magnitude of external transient overvoltage (mainly attributed to lightning), 2178
to which the equipment is exposed, depends on the location of the equipment. 2179
This idea is described in Table 14 of IEC 62368-1:2018 and also specified in 2180
IEC 60664-1. 2181
In response to this idea, IEC 61051-2 has been revised taking into account the 2182
location of the equipment, which also influences the requirement for the 2183
varistors used in the equipment. 2184
The combination pulse test performed according to G.8.2 of IEC 62368-1:2018 2185
can now refer to the new IEC 61051-2 with Amendment 1. 2186
G.9 Integrated circuit (IC) current limiters 2187
Source: IEC 60730-1, IEC 60950-1 2188
Rationale: Integrated circuits (containing numerous integral components) are frequently 2189
used for class 1 and class 2 energy source isolation and, more frequently ( for 2190
example, USB or PoE), for functions such as current limiting. 2191
IEC 60335 series already has requirements for “electronic protect ion devices,” 2192
where conditioning tests such as EMF impulses are applied to such ICs, and 2193
the energy source isolation or current limiting function is evaluated after 2194
conditioning tests. When such energy isolation or current limitation has been 2195
proven reliable via performance, pins on the IC associated with this energy 2196
isolation or limitation are not shorted. 2197
For ICs used for current limitation, t wo test programs were used in 2198
IEC 60950-1:2009. An additional program was developed in IEC 62368-1:2010. 2199
It was felt that all three programs were considered adequate. Therefore , the 2200
three methods were kept. 2201
An Ad Hoc formed at the March 2015, Northbrook HBSDT meeting revised this 2202
test program with the following guiding principles: 2203
a) Streamline the number of tests in overall test program to concentrate on 2204
those tests and conditions that most likely will identify deficiencies in IC 2205
Current Limiter design from a safety perspective, such as allowing more 2206
current to flow than designed for. Some of the existing conditions are 2207
redundant or have questionable value identifying such deficiencies. 2208
b) Focus on test conditions that are applicable for semiconductor devices 2209
rather than test conditions more suited for traditional electro -mechanical 2210
devices. For example, 10 000-cycle testing has more applicability to 2211
electro-mechanical devices (in relation to parts wearing out) versus 2212
semiconductor devices (such as IC current limiters). 2213
c) Combine test conditions when justified to increase efficiency when 2214
conducting individual tests, also trying to make the testing more 2215
compatible with automated testing processes (e.g. combine individual 2216
temperature tests as individual sub-conditions of other required tests). 2217
Table G.10 provides the specific performance test program for IC current 2218
limiters. 2219
IEC TR 62368-2:20xx © IEC 2019 – 145 –
– Input loading to the device should be representative of the manufacturer’s 2220
IC specification (as typically communicated in the IC application notes for 2221
the particular device). 2222
– Output loading is intended to represent a short circuit condition (0 Ω 2223
shunt), with parallel capacitive loading (470 µF +/- 20 %) to better 2224
accommodate on/off cycling. 2225
See Figure 47 in this document for additional detail. 2226
2227
Figure 47 – Example of IC current limiter circuit 2228
Regarding the 250 VA provision, this provision is intended to mean that the 2229
usual test power source has 250 VA capability as long as the IC is designed for 2230
installation in a system with a source of 250 VA or larger. If the power source 2231
capability is intended to be less than 250 VA, then the manufacturer must 2232
specify so, or test in the end product. Testing at 250 VA is intended to include 2233
250 VA or larger sources because the test program is covering relatively small 2234
and low-voltage silicon devices – if these devices pass at 250 VA they likely 2235
would pass at higher VA too since they are not electro -mechanical. Also, this 2236
allows for more practical associated certification test programs. 2237
Also, to avoid recertification of existing components , IC current limiters that 2238
met a previous legacy test program (G.9.2, G.9.3 or G.9.4) are an equivalent 2239
level of safety as the proposed rewritten Clause G.9, primarily because Clause 2240
G.9 is derivation of the legacy requirements. Therefore, IC current limiters that 2241
comply with the legacy test program should not need to be reinvestigated to 2242
the latest document that includes this revised Clause G.9. However, this is a 2243
certification consideration outside the scope of this technical committee. 2244
G.11 Capacitors and RC units 2245
Source: IEC 60384-14:2005 2246
Rationale: Table G.11: Test voltage values aligned with those used in IEC 60384-14 2247
(Tables 1, 2 and 10 of IEC 60384-14:2005). 2248
Table G.12: Minimum number of Y capacitors based on required withstand 2249
voltage of Table 25 of IEC 62368-1:2018. 2250
Table G.13: Maximum voltage that can appear across a Y capacitor based on 2251
the peak value of the working voltage of Table 26 of IEC 62368-1:2018. 2252
Table G.14: Minimum number of Y capacitors based on the test voltages (due 2253
to temporary overvoltages) of Table 27 of IEC 62368-1:2018. 2254
– 146 – IEC TR 62368-2:20xx © IEC 2019
Table G.15: Minimum number of X capacitors (line to line or line to neutral) 2255
based on the mains transient withstand voltage of Table 13 of 2256
IEC 62368-1:2018. 2257
All of the above are aligned with the requirements of IEC 60384-14. 2258
G.13 Printed boards 2259
Source: IEC 60950-1 or IEC 60664-3:2003. 2260
Purpose: To provide details for reliable construction of PCBs. 2261
Rationale: This proposal is based on IEC 60664-3 and the work of IBM and UL in testing 2262
coatings on printed boards when using coatings to achieve insulation 2263
coordination of printed board assemblies. Breakdown voltages of more than 2264
8 000 V for 0,025 mm were routinely achieved in this program. 2265
These parts have multiple stresses on the materials with limited separation 2266
between conductors. This section is taken from IEC 60950-1, where these 2267
requirements have been used for many years. 2268
G.13.6 Tests on coated printed boards 2269
Purpose: Prevent breakdown of the insulation safeguard. 2270
Rationale: Avoid pinholes or bubbles in the coating or breakthrough of conductive tracks 2271
at corners. 2272
G.14 Coatings on component terminals 2273
Source: IEC 60950-1 and IEC 60664-3 2274
Purpose: The mechanical arrangement and rigidity of the terminations are adequate to 2275
ensure that, during normal handling, assembly into e quipment and subsequent 2276
use, the terminations will not be subject to deformation which would crack the 2277
coating or reduce the separation distances between conductive parts. 2278
Rationale: The terminations are treated like coated printed boards (see G.13.3) and the 2279
same separation distances apply. 2280
This section is taken from IEC 60950-1 where these requirements have been 2281
used for many years. 2282
G.15 Pressurized liquid filled components 2283
Source: IEC 60950-1, IEC 61010-1, UL 2178, UL 1995 2284
Purpose: Avoid spillage of liquids resulting in electric shock hazard 2285
Rationale: The requirements apply to devices that contain less than 1 l of liquid. A leak in 2286
the system may result in a shock hazard and therefore, needs to be properly 2287
addressed. A leak is not desirable and ther efore, a strict performance criterion 2288
is proposed. Requirements were developed based on the following description 2289
of a typical system using liquid filled heat sinks. If a different type of system is 2290
used, then the requirements need to be re-evaluated. 2291
Liquid filled heat-sink system (LFHS): a typical system consists of a heat 2292
exchanger, fan, pump, tubing, fittings and cold plate or radiator type heat 2293
exchanger. The liquid filled heat sink comes from the vendor already charged, 2294
sealed; and is installed and used inside the equipment (small type, typically 2295
found in cell stations and computing devices or other types of systems). The 2296
proposed requirements are based on a LFHS being internal to a unit, 2297
used/installed adjacent/over ES1 circuits, in proximity to an enclosed power 2298
supply (not open frame). 2299
IEC TR 62368-2:20xx © IEC 2019 – 147 –
The liquid-filled heat components are used in desktop units or stationary 2300
equipment and in printers. These are not used in any portable equipment 2301
where orientation may change (unless the product is tested in all such 2302
orientations. If the liquid heat sink system is of a sealed type construction, then 2303
the system is orientation proof (this should not be a concern but a good 2304
engineering practice is that the pump does not become the high point in the 2305
system). 2306
Following assumptions are used: 2307
– The tubing is a single-layered metal (copper or aluminium) or non -metallic 2308
construction. If it is non-metallic, flammability requirements will apply. 2309
– The fittings are metal. If it is non-metallic, flammability requirements will 2310
apply. 2311
– Working pressure is determined under normal operating conditions and 2312
abnormal operating conditions and construction (tubing, fitting, heat 2313
exchanger, any joints, etc.) is suitable for this working pressure; 2314
– The volume of the liquid is reasonable (less than 1 000 ml). 2315
– The fluid does not cause corrosion and is not flammable (for example, 2316
corrosion resistant and non-flammable liquid). 2317
– The liquid is non-toxic as specified for the fluid material. 2318
___________ 2319
Annex H Criteria for telephone ringing signals 2320
H.2 Method A 2321
Source: IEC 62949:2016. 2322
Rationale: Certain voltages within telecommunication networks often exceed the steady 2323
state, safe-to-touch limits set within general safety documents. Years of 2324
practical experience by world-wide network operators have found ringing and 2325
other operating voltages to be electrically safe. Records of accident statistics 2326
indicate that electrical injuries are not caused by operating voltages. 2327
Access to connectors carrying such signals with the standard test finger is 2328
permitted, provided that inadvertent access is unlikely. The likelihood of 2329
inadvertent access is limited by forbidding access with the test probe Figure 2C 2330
of IEC 60950-1:2013 that has a 6 mm radius tip. 2331
This requirement ensures that: 2332
– contact by a large part of the human body, such as the back of the hand, is 2333
impossible; 2334
– contact is possible only by deliberately inserting a small part of the body, 2335
less than 12 mm across, such as a fingertip, which presents a high 2336
impedance; 2337
– the possibility of being unable to let -go the part in contact does not arise. 2338
This applies both to contact with signals arriving from the network and to 2339
signals generated internally in the equipment, for example, ringing signals for 2340
extension telephones. By normal standards, these internally generated sign als 2341
would exceed the voltage limits for accessible parts, but the first exemption in 2342
IEC 60950-1 states that limited access should be permitted under the above 2343
conditions. 2344
Ventricular fibrillation of the heart is considered to be the main cause of death 2345
by electric shock. The threshold of ventricular fibrillation (Curve A) is shown in 2346
Figure 48 in this document and is equivalent to curve c1 of IEC 2347
TS 60479-1:2005, Figure 14. The point 500 mA/100 ms has been found to 2348
correspond to a fibrillation probability of the order of 0,14 %. The let go limit 2349
– 148 – IEC TR 62368-2:20xx © IEC 2019
(Curve B) is equivalent to curve 2 of IEC TS 60479-1:2005, Figure 14. Some 2350
experts consider curve A to be the appropriate limit for safe design, but use of 2351
this curve is considered as an absolute limit. 2352
2353
Figure 48 – Current limit curves 2354
Contact with telecommunication operating voltages (EN 41003) 2355
Total body impedance consists of two parts, the internal body resistance of 2356
blood and tissue and the skin impedance. Telecommunication voltages hardly 2357
reach the level where skin impedance begins to rapidly decrease due to 2358
breakdown. The skin impedance is high at low voltages, its value varying 2359
widely. The effects of skin capacitance are negligible at ringing freque ncies. 2360
IEC TS 60479-1 body impedance figures are based upon a relatively large 2361
contact area of 50 cm2 to 100 cm2, which is a realistic value for mains 2362
operated domestic appliances. Practical telecommunication contact is likely to 2363
be much less than this, typically 10 cm2 to 15 cm2 for uninsulated wiring pliers 2364
or similar tools and less than 1 cm2 for finger contact with pins of a telephone 2365
wall socket. For contact with thin wires, wiring tags or contact with tools where 2366
fingers move beyond insulated handles, the area of contact will again be of the 2367
order of 1 cm2 or less. These much smaller areas of contact with the body 2368
produce significantly higher values of body impedance than the IEC TS 60479 2369
figures. 2370
In IEC 60950-1, a body model value of 5 k is used to provide a margin of 2371
safety compared with the higher practical values of body impedance for typical 2372
telecommunication contact areas. 2373
The curve B' [curve C1 of IEC TS 60479-1:2005, Figure 22 (curve A in this 2374
document)] used within the hazardous voltage defini tion is a version of curve B 2375
modified to cover practical situations, where the current limit is maintained 2376
constant at 16 mA above 1 667 ms. This 16 mA limit is still well within the 2377
minimum current value of curve A. 2378
The difficulties of defining conditions that will avoid circumstances that prevent 2379
let-go have led to a very restricted contact area being allowed. 2380
Contact with areas up to 10 cm2 can be justified and means of specifying this 2381
and still ensuring let-go are for further study. 2382
IEC TR 62368-2:20xx © IEC 2019 – 149 –
H.3 Method B 2383
Source: This method is based on USA CFR 47 ("FCC Rules") Part 68, Sub part D, with 2384
additional requirements that apply under fault conditions. 2385
___________ 2386
Annex J Insulated winding wires for use without interleaved insulation 2387
Source: IEC 60851-3:2009, IEC 60851-5:2008, IEC 60851-6:1996 2388
Purpose: Winding wires shall withstand mechanical, thermal and electrical stress during 2389
use and manufacturing. 2390
Rationale: Test data indicates that there is not a major difference between rectangular 2391
wires and round wires for electr ic strength after the bend tests. Therefore, 2392
there is no reason to not include them. 2393
Subclause 4.4.1 of IEC 60851-5:2008 covers only solid circular or stranded 2394
winding wires as a twisted pair can easily be formed from round wires. It is 2395
difficult to form a twisted pair from square or rectangular winding wires. 2396
IEC 60851-5:2008, 4.7 addresses a test method that can be used for square 2397
and rectangular wires. A separate test method for square and rectangular wires 2398
has been added. The test voltage is chosen to be half of the twisted pair as a 2399
single conductor is used for the testing. 2400
In addition, the edgewise bend test is not required by IEC 60851-5 and 2401
IEC 60851-6 for the rectangular and square winding wires. 2402
The reference to trichloroethane is being deleted a s trichloroethane is an 2403
environmentally hazardous substance. 2404
For J.2.3 (Flexibility and adherence) and J.2.4 (Heat shock), 5.1.2 in Test 8 of 2405
IEC 60851-3:2009 and 3.2.1 of IEC 60851-6:1996 are not used for solid square 2406
and solid rectangular winding wires. 2407
___________ 2408
Annex K Safety interlocks 2409
Source: IEC 60950-1 2410
Purpose: To provide reliable means of safety interlock devices. 2411
Rationale: Safety interlock constructions have been used for many years in products 2412
within the scope of this document. Safety interlocks should not be associated 2413
with electro-mechanical components only. 2414
K.7.1 Safety interlocks 2415
Source: IEC 60950-1 2416
Purpose: To provide reliable means of safety interlock devices. 2417
Rationale: Clearance values specified in 5.4.2 are based on IEC 60664 -1 and are 2418
specified for protection against electric shock. The values are the shortest 2419
distance through air between two different conduct ive parts. In that context, 2420
one conductor is at hazardous voltage (energy source) and another conductor 2421
is accessible to a person (body part). The required clearance is the minimum 2422
distance required to protect the person from being exposed to current causing 2423
electric shock. The distance acts as a safeguard against the hazardous energy 2424
source (ES2/ES3). 2425
– 150 – IEC TR 62368-2:20xx © IEC 2019
Contact gaps of interlock relays or switches are most likely not directly serving 2426
as the safeguard as explained above. Instead, the gap is meant to interrupt 2427
the electrical power to the energy sources, for example, motors generating 2428
MS2/3 energy or laser units generating Class IIIb or larger energy. In this 2429
situation, the distance of the gap is required to interrupt the power supply to 2430
the device so that the device is shut down. Again, it is not for the purpose of 2431
blocking current to a body part. 2432
Although the purpose of the clearance is different, the required values based 2433
on IEC 60664-1 are used because there is no other data available addressing 2434
the minimum values required to establish circuit interruption to shut off the 2435
power to a load device. It is believed that the distance req uired to protect a 2436
person from shock hazard is sufficient to have a circuit interruption as part of 2437
proper circuit operation. The specified voltage in clause 5.4 is from 330 Vpeak 2438
or Vdc, and the contacts for interlock relays/switches most likely operate in DC 2439
low voltage such as 5 or 24 V, so much lower than 330 V. Mains operated 2440
contacts are required to have a gap for disconnect device that is much larger 2441
than the distance for insulation. 2442
Due to the above considerations, slight adjustment by altitude mult iplication 2443
factor is not considered necessary for contact gaps of interlock relays/switches. 2444
___________ 2445
Annex L Disconnect devices 2446
Source: IEC 60950-1 2447
Purpose: To provide adequate protective earth connection. 2448
Rationale: 3 mm separation distances of contac ts. Can be part of building installation. 2449
For class I equipment, the supply plug or appliance coupler, if used as the 2450
disconnect device, shall make the protective earthing connection earlier 2451
than the supply connections and shall break it later than the su pply 2452
connections. 2453
Clearance of 3 mm can withstand peak impulse voltages of 4 000 V, which 2454
corresponds to a transient overvoltage present in overvoltage category III 2455
environment (equipment as part of the building installation). 2456
One instructional safeguard could be used for more than one disconnect 2457
device, as long as it can be visible from each disconnect point. 2458
___________ 2459
Annex M Equipment containing batteries and their protection circuits 2460
M.1 General requirements 2461
Rationale: Stand-alone battery chargers for general purpose batteries shall be evaluated 2462
using their relevant safety document, and not IEC 62368-1. If the battery and 2463
the charger are designed specifically for AV or ICT equipment and not to be 2464
used for other purposes, the provisions of IEC 62368-1:2018 including 2465
Annex M may be applied. 2466
IEC TR 62368-2:20xx © IEC 2019 – 151 –
M.2 Safety of batteries and their cells 2467
Rationale: Equipment containing batteries shall be designed to reduce the risk of fire, 2468
explosion and chemical leaks under normal operating conditions and after a 2469
single fault condition in the equipment, including a fault in circuitry within the 2470
equipment battery pack. For batteries replaceable by an ordinary person or 2471
an instructed person, the design shall provide safeguards against reverse 2472
polarity installation or replacement of a battery pack from different component 2473
manufacturers if this would otherwise defeat a safeguard. 2474
Other clauses in this document address in generic terms safeguards 2475
associated with the use of batteries. This annex does not specifically address 2476
those safeguards, but it is expected that batteries and associated circuits 2477
conform to the relevant requirements in this document. 2478
This annex addresses safeguards that are unique to batteries and that are not 2479
addressed in other parts of the document. Energy sources that arise from the 2480
use of batteries are addressed in this annex and include the following: 2481
– situations where the battery is in a state that exceeds its specifications or 2482
ratings (for example, by overcharging, rapid-charge, rapid-discharge, 2483
overcurrent or overvoltage conditions); 2484
– thermal runaway due to overcharge or short circuits within battery cells; 2485
– reverse-charging of the battery; 2486
– leakage or spillage of electrolyte; 2487
– emission of explosive gases; and 2488
– location of safeguards where battery packs may be replaceable by an 2489
ordinary person or an instructed person. 2490
Thermal runaway in the cell can result in explosion or fire, when the 2491
temperature rise in the cell caused by the heat emission raises the internal cell 2492
pressure faster than can be released by the cell pressure release device. 2493
Thermal runaway can be initiated by several causes: 2494
– defects introduced into the cell during cell construction. These defects are 2495
often not detected during the manufacturing process and may bridge an 2496
internal insulation layer or block a vent; 2497
– over-charge and rapid-charge or rapid-discharge; 2498
– high operational temperature or high battery environment temperature; 2499
– other cells in a pack feeding energy to a fault in a single cell; and 2500
– crushing of the enclosure. 2501
NOTE Batteries may contain multiple cells. 2502
During charging operation, gases are emitted from secondary cells and 2503
batteries excluding gastight sealed (secondary) cells, as the result of the 2504
electrolysis of water by electric current. Gases produced are hydrogen and 2505
oxygen. 2506
Table 17 in this document gives an overview of the referenced battery 2507
documents. 2508
2509
–
15
2 –
IE
C T
R 6
23
68
-2:2
01
9 ©
IEC
20
19
Table 17 – Safety of batteries and their cells – requirements (expanded information on documents and scope) 2510
Document
Chemistry Category Movability
Scope (details)
Alk
ali
ne
; n
on
-ac
id
Le
ad
Ac
id
NiC
d/N
iMH
Lit
hiu
m
Nic
ke
l; a
lka
lin
e
ele
ctr
oly
te
Va
rio
us
Va
rio
us
, w
ith
aq
ue
ou
s e
lec
tro
lyte
Pri
ma
ry
Se
co
nd
ary
Po
rta
ble
Sta
tio
na
ry
All
IEC 60086-4 (2014); Primary Batteries – Part 4 – Safety of Lithium Batteries
X X X Specifies tests and requirements for primary lithium batteries to ensure their safe operation under intended use and reasonably foreseeable misuse (includes coin / button cell batteries).
IEC 60086-5 (2016): Primary Batteries – Part 5 – Safety of batteries with aqueous electrolyte
X X X Specifies tests and requirements for primary batteries with aqueous electrolyte to ensure their safe operation under intended use and reasonably foreseeable misuse (includes coin/button cell batteries ).
IEC 60896-11 (2002): Stationary Lead Acid Batteries – Part 11 – Vented type
X X X X Applicable to lead-acid cells and batteries that are designed for service in fixed locations ( for example, not habitually to be moved from place to place) and which are permanently connected to the load and to the DC power supply. Batteries operating in such applications are called "stationary batteries". Any type or construction of lead -acid battery may be used for stationary battery applications. Part 11 is applicable to vented types only.
IEC 60896-21 (2004): Stationary Lead Acid Batteries – Part 21 – Valve regulated type – method of test
X X X X Applies to all stationary lead -acid cells and monobloc batteries of the valve regulated type for float charge applications, (for example, permanently connected to a load and to a DC power supply), in a static location (for example, not generally intended to be moved from place to place) and incorporated into stationary equipment or installed in battery rooms for use in telecom, uninterruptible power supply (UPS), utility switching, emergency power or similar applications. The objective is to specify the methods of test for all types and construction of valve regulated stationary lead acid cells and monobloc batteries used in standby power applications.
IEC
TR
62
36
8-2
:20
19
© IE
C 2
01
9
– 1
53
–
Document
Chemistry Category Movability
Scope (details) A
lka
lin
e;
no
n-a
cid
Le
ad
Ac
id
NiC
d/N
iMH
Lit
hiu
m
Nic
ke
l; a
lka
lin
e
ele
ctr
oly
te
Va
rio
us
Va
rio
us
, w
ith
aq
ue
ou
s e
lec
tro
lyte
Pri
ma
ry
Se
co
nd
ary
Po
rta
ble
Sta
tio
na
ry
All
IEC 60896-22 (2004): Stationary Lead Acid Batteries – Part 22 – Valve regulated type – requirements
X X X X Applies to all stationary lead -acid cells and monobloc batteries of the valve regulated type for float charge applications, (for example, permanently connected to a load and to a DC power supply), in a static location ( for example, not generally intended to be moved from place to place) and incorporated into stationary equipment or installed in battery rooms for use in telecom, uninterruptible power supply (UPS), utility switching, emergency power or similar applications. The objective is to assist the specifier in the understanding of the purpose of each test containe d within IEC 60896-21 and provide guidance on a suitable requirement that will result in the battery meeting the needs of a particular industry application and operational condition. This document is used in conjunction with the common test methods described in IEC 60896-21 and is associated with all types and construction of valve regulated stationary lead-acid cells and monobloc batteries used in standby power applications.
IEC 61056-1 (2012): General purpose lead-acid batteries (valve-regulated types) – Part 1: General requirements, functional characteristics – Methods of test
X X X X Specifies the general requirements, functional characteristics and methods of test for all general-purpose lead-acid cells and batteries of the valve-regulated type:
– for either cyclic or float charge application;
– in portable equipment, for instance, incorporated in tools, toys, or in static emergency, or uninterruptible power supply and general power supplies.
(For stationary applications, the battery will need to meet IEC 60896-21/-22 or subject to additional evaluation) .
–
15
4 –
IE
C T
R 6
23
68
-2:2
01
9 ©
IEC
20
19
Document
Chemistry Category Movability
Scope (details) A
lka
lin
e;
no
n-a
cid
Le
ad
Ac
id
NiC
d/N
iMH
Lit
hiu
m
Nic
ke
l; a
lka
lin
e
ele
ctr
oly
te
Va
rio
us
Va
rio
us
, w
ith
aq
ue
ou
s e
lec
tro
lyte
Pri
ma
ry
Se
co
nd
ary
Po
rta
ble
Sta
tio
na
ry
All
IEC 61056-2 (2012): General purpose lead-acid batteries (valve-regulated types) – Part 2: Dimensions, terminals and marking
X X X X Specifies the dimensions, terminals and marking for all general-purpose lead-acid cells and batteries of the valve regulated type:
– for either cyclic or float charge application;
– in portable equipment, for instance, incorporated in tools, toys, or in static emergency, or uninterruptible power supply and general power supplies.
(For stationary applications, the battery will need to meet IEC 60896-21/-22 or subject to additional evaluation) .
IEC 61427 (all parts) (2013): Secondary cells and batteries for renewable energy storage – General requirements and methods of test – Part 1: Photovoltaic off-grid application
X X X Part of a series that gives general information relating to the requirements for the secondary batteries used in photovoltaic energy systems (PVES) and to the typical methods of test used for the verification of battery performances. This part deals with cells and batteries used in photovoltaic off -grid applications. This document is applicable to all types of secondary batteries.
IEC TS 61430 (1997): Secondary Cells and Batteries – Test Methods for Checking the Performance of Devices Designed for Reducing Explosion Hazards – Lead-Acid Starter Batteries
X X X Specification gives guidance on procedures for testing the effectiveness of devices which are used to reduce the hazards of an explosion, together with the protective measures to be taken.
IEC 61434 (1996): Secondary cells and batteries containing alkaline or other non-acid electrolytes Guide to the designation of current in alkaline secondary cell and battery standards
X X X Applies to secondary cells and batteries containing alkaline or other non-acid electrolytes. It proposes a mathematically correct method of current designation which shall be used in future secondary cell and battery documents.
IEC
TR
62
36
8-2
:20
19
© IE
C 2
01
9
– 1
55
–
Document
Chemistry Category Movability
Scope (details) A
lka
lin
e;
no
n-a
cid
Le
ad
Ac
id
NiC
d/N
iMH
Lit
hiu
m
Nic
ke
l; a
lka
lin
e
ele
ctr
oly
te
Va
rio
us
Va
rio
us
, w
ith
aq
ue
ou
s e
lec
tro
lyte
Pri
ma
ry
Se
co
nd
ary
Po
rta
ble
Sta
tio
na
ry
All
IEC 61959 (2004): Secondary cells and batteries containing alkaline or other non-acid electrolytes Mechanical tests for sealed portable secondary cells and batteries
X X X Specifies tests and requirements for verifying the mechanical behavior of sealed portable secondary cells and batteries during handling and normal use.
IEC 62133 (all parts) (2012 – superseded by IEC 62133-1 and IEC 62133-2); Secondary cells and batteries containing alkaline or other non-acid electrolytes – Safety requirements for portable sealed secondary cells, and for batteries made from them, for use in portable applications
X X X Specifies requirements and tests for the safe operation of portable sealed secondary cells and batteries (other than coin / button cell batteries) containing alkaline or other non-acid electrolyte, under intended use and reasonably foreseeable misuse .
IEC 62133-1 (2017): Secondary cells and batteries containing alkaline or other non-acid electrolytes – Safety requirements for portable sealed secondary cells, and for batteries made from them, for use in portable applications – Part 1: Nickel systems
X X X Specifies requirements and tests for the safe operation of portable sealed secondary nickel cells and batteries containing alkaline electroly te, under intended use and reasonably foreseeable misuse.
IEC 62133-2 (2017): Secondary cells and batteries containing alkaline or other non-acid electrolytes – Safety requirements for portable sealed secondary lithium cells, and for batteries made from them, for use in portable applications – Part 2: Lithium systems
X X X Specifies requirements and tests for the safe operation of portable sealed secondary lithium cells and batteries containing non-acid electrolyte, under intended use and reasonably foreseeable misuse .
–
15
6 –
IE
C T
R 6
23
68
-2:2
01
9 ©
IEC
20
19
Document
Chemistry Category Movability
Scope (details) A
lka
lin
e;
no
n-a
cid
Le
ad
Ac
id
NiC
d/N
iMH
Lit
hiu
m
Nic
ke
l; a
lka
lin
e
ele
ctr
oly
te
Va
rio
us
Va
rio
us
, w
ith
aq
ue
ou
s e
lec
tro
lyte
Pri
ma
ry
Se
co
nd
ary
Po
rta
ble
Sta
tio
na
ry
All
IEC 62281 (2016): Safety of primary and secondary lithium cells and batteries during transport
X X X X Specifies test methods and requirements for primary and secondary (rechargeable) lithium cells and batteries to ensure their safety during transport other than for recycling or disposal (similar to UN 38.3 ).
IEC 62485-2
(2010): Safety requirements for secondary batteries and battery installations – Part 2: Stationary batteries
X X X X Applies to stationary secondar y batteries and battery installations with a maximum voltage of 1 500 V DC (nominal) and describes the principal measures for protections against hazards generated from:
– electricity,
– gas emission,
– electrolyte.
Provides requirements on safety aspects associated with the erection, use, inspection, maintenance and disposal. It covers lead-acid and NiCd/NiMH batteries (IEC 62485-2 requires the valve regulated batteries to meet safety requirements from IEC 60896).
IEC 62619 (2017): Secondary cells and batteries containing alkaline or other non-acid electrolytes – Safety requirements for secondary lithium cells and batteries, for use in industrial applications
X X X Specifies requirements and tests for the safe operation of secondary lithium cells and batteries used in industrial applications including stationary applications.
2511
2512
IEC TR 62368-2:2019 © IEC 2019 – 157 –
M.3 Protection circuits for batteries provided within the equipment 2513
Rationale: Equipment containing batteries is categorized into two types; 2514
1. Equipment containing batteries which are embedded in the equipment and 2515
cannot be separated from the equipment. 2516
2. Equipment containing batteries which can be separated from the 2517
equipment. 2518
The requirements in IEC 62368-1 cover only the battery circuits that are not an 2519
integral part of the battery itself, and as such form a part of the equipment. 2520
M.4 Additional safeguards for equipment containing a portable secondary 2521
lithium battery 2522
Rationale: M.4 applies to all equipment with lithium batteries. M.4.4 applies only to 2523
equipment as specified in clause M.4.4 (typically portable). 2524
Secondary lithium batteries (often called lithium-ion or li-ion batteries) are 2525
expected to have high performance, such as light-weight and high energy 2526
capability. The use of li -ion batteries has been continuously expanding in the 2527
area of high-tech electronic equipment. However, it is said that this technology 2528
involves risks because the safety margin (distance between safe -operation 2529
zone and unsafe-operation zone) is relatively small compared to other battery 2530
technologies. 2531
IEC TC 108 noted that for designing equipment containing or using li -ion 2532
battery, it is imperative to give careful consideration to selecting highly reliable 2533
battery cells, providing high performance battery management systems for 2534
operating batteries within their specified operating environment and parameter 2535
range (for example, battery surrounding temperature or battery 2536
charging/discharging voltage and current) . It is also imperative to introduce 2537
safeguards against abnormal operating conditions, such as vibration during 2538
the use of devices, mechanical shock due to equipment drop, surge signals 2539
caused internally or externally, and a mechanism to reduce the likelihood of 2540
catastrophic failure such as battery explosion or fire. 2541
It is suggested that suppl iers of equipment and batteries should take into 2542
account possible abnormal operating conditions that may occur during use, 2543
transport, stock, and disposal, so that the equi pment is well prepared for such 2544
conditions. 2545
It is important that the key parameters (highest/lowest charging temperatures, 2546
maximum charging current, and upper limit charging voltage) during charging 2547
and discharging of the battery are not exceeded. 2548
IEC TC 108 noted that, when designing battery compartments, the battery 2549
compartment dimensions should allow sufficient space for cells to expand 2550
normally under full operating temperature range or be flexible to prevent 2551
unnecessary compression of the cells. Given the wide range of battery 2552
constructions, corresponding battery compartment dimensional requirements 2553
will differ. When necessary, coordinate with the battery manufacturer to 2554
determine change in battery dimensions over full operating range during 2555
charging and discharging. 2556
M.4.2.2 Compliance criteria 2557
The highest temperature point in the battery may not always exist at the center 2558
of the battery. The battery supplier should specify the point where the highest 2559
temperature in the battery occurs. 2560
To test the charging circuit, instead of using a real battery (which is a chemical 2561
system), an electrical circuit emulating the battery behavior (dummy battery 2562
circuit) may make the test easier by eliminating a possible battery defect. 2563
An example of a dummy battery circuit is given in Figure 49 in this document. 2564
Met opmerkingen [RJ8]: See Raleigh minutes 9.4.8
– 158 – IEC TR 62368-2:2019 © IEC 2019
Figure 49 – Example of a dummy battery circuit
M.4.3 Fire enclosure 2565
Lithium-ion batteries with an energy more than PS1 (15 W) must be provided 2566
with a fire enclosure (either at the battery or at the equipment containing the 2567
battery) because even though measurements of output voltage and current 2568
may not necessarily show them to be a PIS, however they contain flammable 2569
electrolyte that can be easily ignited by the enormous amount of heat 2570
developed by internal shorts as a result of possibl e contaminants in the 2571
electrolyte. 2572
M.4.4 Drop test of equipment containing a secondary lithium battery 2573
Annex M.4.4 applies only to batteries used in portable applications. 2574
This includes batteries in the scope of IEC 62133 and IEC 62133 -2 which are 2575
typically used in hand-held equipment or transportable equipment. 2576
Batteries or sub-assemblies containing batteries used in other types of 2577
equipment, that are not routinely held or carried but may be occasionally 2578
removed for service or replacement, are not conside red to be portable batteries 2579
and are not in scope of Annex M.4.4. 2580
Monitoring of lithium-ion battery output voltage and surface temperature during 2581
or after the drop test may not help. The concern is that if a minor dent occurs, 2582
nothing may happen to the battery. Temperature may go up slightly and then 2583
drop down without any significant failure. If the battery is damaged, the 2584
damage may only show up if the battery is then subjected to few charging and 2585
discharging cycles. Therefore, the surface temperature measurement was 2586
deleted and replaced with charging and discharging cycles after the drop test. 2587
The charging and discharging of the battery shall not result in any fire or 2588
explosion. 2589
It is important that the equipment containing a secondary lithium battery 2590
needs to have a drop impact resistance. Equipment containing a secondary 2591
lithium battery should avoid further damage to the control circuit and the 2592
batteries. 2593
As M.4.4 requires the equipment to be tested, the relevant equipment heights 2594
need to be used instead of the height for testing parts that act as a fire 2595
enclosure. 2596
After the drop test: 2597
– Initially, the control functions should be checked to determine if they 2598
continue to operate and all safeguards are effective. A dummy battery or 2599
appropriate measurement tool can be used for checking the function of the 2600
equipment. 2601
Met opmerkingen [RJ9]: See Raleigh minutes 7.1.4
Met opmerkingen [JR10]: See Shanghai meeting minutes item 6.1.21
IEC TR 62368-2:2019 © IEC 2019 – 159 –
– Then, the batteries are checked whether or not a slight internal short circuit 2602
occurs. 2603
Discharge and charge cycles under normal operating conditions test hinder 2604
detection of the slight internal short circuit because the current to discharge 2605
and charge is higher than the current caused by a slight internal short circuit. 2606
Thus, it is very important to conduct a voltage observation of the battery 2607
immediately after the drop test without any discharge and charge. 2608
To detect a slight internal short circuit of the battery, IEC TC 108 adopts a no-2609
load test, which can detect a battery open voltage drop caused by an internal 2610
short circuit leak current in a 24 h period. 2611
Equipment containing an embedded type of battery has internal power 2612
dissipation (internal consumption current). Therefore, two samples of the 2613
equipment are prepared, one for the drop test and the other for reference in a 2614
standby mode. In this way, the effect of internal power dissipation can be 2615
detected by measuring a difference between voltage drops in the 24 h period. 2616
M.6.1 Requirements 2617
Examples: Examples of battery documents containing an internal short test are 2618
IEC 62133, IEC 62133-2 and IEC 62619. 2619
Another example of compliance to internal fault requirements is a battery using 2620
cells that have passed the impact test as specified in IEC 62281. 2621
M.7.1 Ventilation preventing an explosive gas concentration 2622
Rationale: During charging, float charging, and overcharging operation, gases are emitted 2623
from secondary cells and batteries excluding gastight sealed (secondary) 2624
cells, as the result of the electrolysis of water by electric current. Gases 2625
produced are hydrogen and oxygen. 2626
M.7.2 Test method and compliance criteria 2627
Source: The formula comes from IEC 62485-2:2010, 7.2. 2628
M.8.2.1 General 2629
Source: The formula comes from IEC 60079-10-1:2015, Clause B.4. 2630
___________ 2631
Annex O Measurement of creepage distances and clearances 2632
Source: IEC 60664-1, IEC 60950-1 2633
Purpose: Clearances are measured from the X-points in the figure 2634
Rationale: Figure O.4. At an IEC/TC 109 meeting in Paris, a draft CTL interpretatio n was 2635
discussed regarding example 11 of IEC 60664 -1. The question was if distances 2636
smaller than X should be counted as zero. There was a quite lengthy debate, 2637
but the conclusion was that, based on the other examples in the standard (and 2638
especially example 1), there is no reason why in this example the distance 2639
should be counted as zero. If this should be done, many other examples should 2640
be changed where it is shown that the distance is measured across X rather 2641
than to disregard X. TC 109 has decided to modi fy the example 11 to remove 2642
the X from the figure to avoid this confusion in future. As IEC 60664 -1 is the 2643
basic safety publication, we should align with this interpretation . Therefore, the 2644
statement that distances smaller than X are disregar ded is deleted from 2645
Figure O.4. 2646 Met opmerkingen [JR11]: See Shanghai meeting minutes item 6.1.22
– 160 – IEC TR 62368-2:2019 © IEC 2019
Figure O.13. The clearance determination is made from the X-points in the 2647
figure, as those are the first contact points when the tes t finger enters the 2648
enclosure opening. It is assumed that the enclosure is covered by conductive 2649
foil, which simulates conductive pollution. 2650
___________ 2651
Annex P Safeguards against conductive objects 2652
P.1 General 2653
Rationale: The basic safeguard against entry of a foreign object is that persons are not 2654
expected to insert a foreign object into the equipment. Where the equipment is 2655
used in locations where children may be present, it is expected that there will 2656
be adult supervision to address the issue of reasonable foreseeable misuse by 2657
children, such as inserting foreign objects . Therefore, the safeguards specified 2658
in this annex are supplementary safeguards. 2659
P.2 Safeguards against entry or consequences of entry of a for eign object 2660
Source: IEC 60950-1 2661
Purpose: Protect against the entry of foreign objects 2662
Rationale: There are two alternative methods that may be used. 2663
P.2.2 specifies maximum size limits and construction of openings. The 2664
relatively small foreign conductive objects or amounts of liquids that may p ass 2665
through these openings are not likely to defeat any equipment safeguards. 2666
This option prevents entry of objects that may defeat a safeguard. 2667
Alternatively, if the openings are larger than those specified in P.2.2, P.2.3 2668
assumes that a foreign conductive object or liquid passing through these 2669
openings is likely to defeat an equipment basic safeguard, and requires that 2670
the foreign conductive object or liquid shall not defeat an equipment 2671
supplementary safeguard or an equipment reinforced safeguard. 2672
P.2.3.1 Safeguard requirements 2673
Rationale: Conformal coating material is applied to electronic circuitry to act as protection 2674
against moisture, dust, chemicals, and temperature extremes that, if uncoated 2675
(non-protected), could result in damage or failure of the electronics to function. 2676
When electronics are subject to harsh environments and added protection is 2677
necessary, most circuit board assembly houses coat assemblies with a layer of 2678
transparent conformal coating rather than potting. 2679
The coating material can be applied by various methods, from brushing, 2680
spraying and dipping, or, due to the increasing complexities of the electronic 2681
boards being designed and with the 'process window' becoming smaller and 2682
smaller, by selectively coating via robot. 2683
P.3 Safeguards against spillage of internal liquids 2684
Source: IEC 60950-1 2685
Rationale:If the liquid is conductive, flammable, toxic, or corrosive, then the liquid shall 2686
not be accessible if it spills out. The container of the liquid provides a basic 2687
safeguard. After the liquid spills out, then barrier, guard or enclosure that 2688
prevents access to the liquid acts as a supplementary safeguard. Another 2689
choice is to provide a container that does not leak or permit spillage for 2690
example, provide a reinforced safeguard. 2691
P.4 Metalized coatings and adhesives securing parts 2692
Source: IEC 60950-1 2693
IEC TR 62368-2:2019 © IEC 2019 – 161 –
Rationale:Equipment having internal barriers secured by adhesive are subject to 2694
mechanical tests after an aging test. If the barrier does not dislodge as a whole 2695
or partially or fall off, securement by adhesive is considered acceptable. 2696
The temperature for conditioning should be based on the actual temperature of 2697
the adhesive secured part. 2698
The test program for metalized coatings is the same as for aging of adhesives. 2699
In addition, the abrasion resistance test is done to see if particles fall off from 2700
the metalized coating. Alternatively, clearance and creepage distances for 2701
PD3 shall be provided. 2702
___________ 2703
Annex Q Circuits intended for interconnection with building wiring 2704
Source: IEC 60950-1:2013 2705
Rationale: For the countries that have electrical and fire codes based on NFPA 70, this 2706
annex is applied to ports or circuits for external circuits that are 2707
interconnected to building wiring for limited power circuits. Annex Q was based 2708
on requirements from IEC 60950-1 that are designed to comply with the 2709
external circuit power source requirements necessary for compliance with the 2710
electrical codes noted above. 2711
Q.1.2 Test method and compliance criteria 2712
In determining if a circuit is a limited power source, all co nditions of use should 2713
be considered. For example, for circuits that may be connected to a battery 2714
source as well as a mains source, determination whether the available output 2715
from the circuit is a limited power source is made with each of the sources 2716
connected independently or simultaneously (see Figure 50 in this document). 2717
Q.2 Test for external circuits – paired conductor cable 2718
Time/current characteristics of type gD and type gN fuses specified in 2719
IEC 60269-2-1 comply with the limit. Type gD or type gN fuses rated 1 A, would 2720
meet the 1,3 A current limit. 2721
2722
Figure 50 – Example of a circuit with two power sources 2723
___________ 2724
Annex R Limited short-circuit test 2725
Source: IEC SC22E 2726
– 162 – IEC TR 62368-2:2019 © IEC 2019
Rationale: The value of 1 500 A is aligned with the normal breaking capacity of a high 2727
breaking fuse. In Japan the prospective short circuit current is considered less 2728
than 1 000 A. 2729
___________ 2730
Annex S Tests for resistance to heat and fire 2731
S.1 Flammability test for fire enclosure and fire barrier materials of equipment 2732
where the steady-state power does not exceed 4 000 W 2733
Rationale: This test is intended to test the ability of an end -product enclosure to 2734
adequately limit the spread of flame from a potential ignition source to the 2735
outside of the product. 2736
– Included the text from IEC 60065 using the needle flame as the ignition 2737
source for all material testing. The reapplication of the flame after the first 2738
flaming was added to clarify that the test flame is immediately re -applied 2739
based on current practices. 2740
– This conditioning requirement of 125 °C for printed wiring boards is derived 2741
from laminate and PCB documents. 2742
S.2 Flammability test for fire enclosure and fire barrier integrity 2743
Rationale: This test method is used to test the integrity of a fire barrier or fire enclosure 2744
where a potential ignition source is in very close proximity to an enclosure 2745
or a barrier. 2746
The criteria of “no additional holes” is considered important as flammable 2747
materials may be located immediately on the other side of the barrier or fire 2748
enclosure. 2749
Rationale: Application of needle flame 2750
The flame cone and the 50 mm distance is a new requirement that was not 2751
applied in IEC 60950 to top openings. This new requirement does impact 2752
already certified IEC 60950 ITE products, and it was found that some 2753
manufacturers’ current designs were not able to comply with the 50-mm 2754
distance prescribed ventilation opening requirements and will not be able to 2755
pass the needle flame test as per IEC 60695-11. An HBSDT’s fire enclosure 2756
adhoc team performed some experimental flame testing with the needle flame 2757
located at various distances from various size ventilation openings. This test 2758
approach was found to align more with hazard-based safety engineering 2759
principles and deemed to be a more realistic representation of when a thermal 2760
event may occur. 2761
A PIS can be in the form of any size/shape , so it was determined not 2762
reasonable to directly apply the needle flame to top surface openings when 2763
realistically a thermal event from smaller components is unlikely to touch the 2764
top surface openings. Additionally, typically it is common for such components 2765
to be mounted on V-0 rated boards that further help reduce the spread of fire. 2766
The test data from the fire experimental testing demonstrat ed clearly that, 2767
when the flame is at distances well within 50 mm, significantly larger openings 2768
can be used beyond the pre-specified sizes by 6.4.8.3.3 ( for example less than 2769
5 mm in any dimension and/or less than 1 mm regardless of length). 2770
Therefore, for the purpose of this standard and to align more with hazard-2771
based safety engineering principles , the needle flame is to be applied at a 2772
distance measured from the closest assessed point of a PIS to the closest 2773
surface point of the test specimen. The appli cation of the flame is measured 2774
from the top of the needle flame burner to the closest surface point. See Figure 2775
S.1 in Clause S.2 of IEC 62368-1:2018. 2776
IEC TR 62368-2:2019 © IEC 2019 – 163 –
S.3 Flammability tests for the bottom of a fire enclosure 2777
Source: IEC 60950-1:2013 2778
Rationale: This text was not changed from the original ECMA document which was 2779
originally in IEC 60950-1. This test is intended to determine the acceptability of 2780
holes or hole patterns in bottom enclosures to prevent flaming material from 2781
falling onto the supporting surface. It has been used principally for testing 2782
metal bottom enclosures. 2783
This test is being proposed to test all bottom enclosures. Research is ongoing 2784
to develop a similar test based on the use of flammable (molten) thermoplastic 2785
rather than oil. 2786
S.4 Flammability classification of materials 2787
Rationale: The tables were considered helpful to explain the hierarchy of material 2788
flammability class requirements used in this document. 2789
Whenever a certain flammability class is required, a better classification is 2790
allowed to be used. 2791
S.5 Flammability test for fire enclosure materials of equipment with a steady 2792
state power exceeding 4 000 W 2793
Source: IEC 60950-1:2013 2794
Rationale: The annex for flammability test for high voltage cables was withdrawn and 2795
replaced by flammability test for fire enclosure materials of equipment having 2796
greater than 4 000 W faults. 2797
___________ 2798
Annex T Mechanical strength tests 2799
T.2 Steady force test, 10 N 2800
Source: IEC 60950-1 2801
Rationale: 10 N applied to components and parts that may be touched during operation or 2802
servicing. This test simulates the accidental contact with a finger or part of a 2803
hand. 2804
T.3 Steady force test, 30 N 2805
Source: IEC 60065 and IEC 60950-1 2806
Rationale: This test simulates accidental contact with a part of the hand. 2807
T.4 Steady force test, 100 N 2808
Source: IEC 60065 and IEC 60950-1 2809
Rationale: This test simulates an expected force applied during use or movement. 2810
T.5 Steady force test, 250 N 2811
Source: IEC 60065 and IEC 60950-1 2812
Rationale: 250 N applied to external enclosures (except those covered in Clause T.4). 2813
This test simulates an expected force when leaning against the equipment 2814
surface to ensure clearances are not bridged to introduce a hazard such as 2815
shock. The 30 mm diameter surface simulates a small part of hand or foot. It is 2816
not expected that such forces will be applied to the bottom surface of heavy 2817
equipment ( 18 kg). 2818
– 164 – IEC TR 62368-2:2019 © IEC 2019
T.6 Enclosure impact test 2819
Source: IEC 60065 and IEC 60950-1 2820
Rationale: To check integrity of the enclosure, to ensure that no hazard is created by an 2821
impact. 2822
The values in T.6 are taken over from existing requirements in IEC 60065 and 2823
IEC 60950-1. 2824
The impact is applied once for each test point on the enclosure. 2825
T.7 Drop test 2826
Source: IEC 60065 and IEC 60950-1 2827
Rationale: This test addresses potential exposure to a hazard after the impact and not 2828
impact directly on a body part. The test is app lied to desk top equipment under 2829
7 kg as it is more likely these products could be accidentally knocked off the 2830
desk. The drop height was chosen based on intended use of the product. 2831
The term “table-top” has been used in IEC 60065, while the term “desk -top” 2832
has been used in IEC 60950-1. Both terms had been taken over in IEC 62368-1 2833
without the intention to make the different requirements for these types of 2834
equipment. Therefore, the requirements are applicable to both type of 2835
equipment even if only either one is referred to. From edition 3 onwards, the 2836
term “table-top” has been replaced by “desk -top”. 2837
T.8 Stress relief test 2838
Source: IEC 60065 and IEC 60950-1 2839
Rationale: To ensure that the mechanical integrity of moulded plastic parts is not affected 2840
by their relaxation or warping following thermal stress. 2841
T.9 Glass impact test 2842
Source: IEC 60065 2843
Rationale: Test applied to test the strength of the glass. 2844
The value of 7 J is a value that has been used for CRT in the past. Except for 2845
that, the value has also been used in commercial applications, but not in 2846
households, where the forces expected on the glass are much lower. CRT’s 2847
have separate requirements in Annex W. Therefore , a value of 3,5 J is 2848
considered sufficient. 2849
The centre of a piece of glass can be determined via the intersection of two 2850
diagonals for a rectangular piece or any other appropriate means for pieces of 2851
other geometries. 2852
T.10 Glass fragmentation test 2853
Source: IEC 60065 2854
Rationale: Test applied to ensure the fragments are small enough to be consid ered at 2855
MS2 level or less. 2856
___________ 2857
Annex U Mechanical strength of CRTs and protection against the effects of 2858
implosion 2859
U.2 Test method and compliance criteria for non-intrinsically protected CRTs 2860
Source: IEC 61965, IEC 60065 2861
IEC TR 62368-2:2019 © IEC 2019 – 165 –
Rationale: The 750 mm simulates the height of a typical supporting surface such as a 2862
table or counter top. Test applied to ensure any expelled fragments are small 2863
enough to be considered at MS2 level or less. The fragment size represents a 2864
grain of sand. The test distances selected ensure fragments do not travel far 2865
enough to strike a person and cause injury. 2866
___________ 2867
Annex V Determination of accessible parts 2868
Figure V.3 Blunt probe 2869
Source: This test probe is taken from Figure 2c, IEC 60950-1:2013 2870
___________ 2871
Annex X Alternative method for determing clearances for insulation in 2872
circuits connected to an AC mains not exceeding 420 V peak (300 V 2873
RMS) 2874
Rationale: IEC TC 108 made a responsible decision to harmonize the requirements for 2875
clearances and creepage distances with the horizontal IEC 60664-x series 2876
documents produced by IEC TC 109. This decision is aligned with IEC 2877
harmonization directives and allows manufacturers the design benefits afforded 2878
by the IEC 60664-x series documents when minimization of spacings is a 2879
primary consideration of the product design. 2880
However, because of the complexity of determining clearances as per 5.4.2, 2881
sometimes the more state-of-art theory is not practical to implement for designs 2882
not requiring minimized spacings. For example, there are a very large number 2883
of existing designs and constructions qualified to IEC 60950-1 that are 2884
associated with products, mainly switch mode power supplies, connected to AC 2885
mains (overvoltage category II) not exceeding 300 V RMS. These 2886
constructions have successfully used the clearance requirements in 2887
IEC 60950-1 without any evidence of field issues, and even at switching 2888
frequencies well above 30 kHz. In fact, almost every switch mode power supply 2889
(SMPS) used today with IT & ICT equipment intended to be connected to 2890
mains less than 300 V RMS, including external power supplies, direct plug -in 2891
type, and internal power supplies, have clearances based on the base 2892
requirements in Subclause 2.10.3.3 and Tables 2K and 2L of IEC 60950-1. 2893
Although the requirements do not incorporate the latest research on 2894
clearances used in circuits operating above 30 kHz, they are considered to be 2895
suitable for the application because they are a conservative implementation of 2896
IEC 60664-1 without minimization. 2897
As a result, and in particular based on their proven history of acceptability in 2898
the broad variety of power supplies used today, IEC TC 108 should support 2899
continued limited application of a prescribed set of clearances as an 2900
alternative to the more state-of-art IEC 60664-based requirements in 2901
IEC 62368-1 today. However, because of the valid concern with circuits 2902
operating above 30 kHz as clearances are further minimized, the IEC 60950-1 2903
option in Tables 2K and 2L for reduced clearances in products with 2904
manufacturing subjected to a quality contro l programme (values in parenthesis 2905
in Tables 2K/2L) are not included in this proposal since the reduced 2906
clearances associated with the quality control option has not been used 2907
frequently under IEC 60950-1, and therefore there is not the same proven track 2908
record of successful implementation in a very large number of products. 2909
Similarly, there is not the same large quantity of qualified designs/construction 2910
associated with equipment connected to mains voltages exceeding 300 V 2911
– 166 – IEC TR 62368-2:2019 © IEC 2019
RMS, or for equipment connected to DC mains, so these constructions should 2912
comply with the existing IEC 60664-based requirements in IEC 62368-1. 2913
___________ 2914
Annex Y Construction requirements for outdoor enclosures 2915
Rationale: General 2916
In preparing the requirements for outdoor enclosures, it has been assumed 2917
that: 2918
– exterior to the outdoor equipment there should be no hazards, just as is 2919
the case with other information technology equipment; 2920
– protection against vandalism and other purposeful acts will be treated as a 2921
product quality issue (for example, IEC 62368-1 does not contain 2922
requirements for the security of locks, types of acceptable screw head, 2923
forced entry tests, etc.). 2924
Electric shock 2925
It is believed that most aspects relating to protection against the risk of electric 2926
shock are adequately covered by IEC 62368-1 including current proposals, and 2927
in some cases, quoted safety documents (in particular, the IEC 60364 series), 2928
and with the exception of the following, do not require modification. Specific 2929
requirements not already suitably addressed in IEC 60950-1 were considered 2930
as follows: 2931
– clearing of earth faults for remotely located (exposed) information 2932
technology equipment; 2933
– the degree of protection provided by the enclosure to rain, dust, etc.; 2934
– the effect of moisture and pollution degree on the insulation of the 2935
enclosed parts; 2936
– the possible consequences of ingress by plants and animals (since these 2937
could bridge or damage insulation); 2938
– the maximum permissible touch voltage and body contact impedance for wet 2939
conditions. 2940
It is noted that the voltage limits of user -accessible circuits and parts in 2941
outdoor locations only are applicable to circuits and parts that are actually 2942
“user-accessible”. If the circuits and parts are not user accessible 2943
(determined via application of accessibility probes) and are enclosed in 2944
electrical enclosures, connectors and cable suitable for the outdoor 2945
application, including being subject to all relevant outdoor enclosure testing, 2946
voltage limits for indoor locations may be acceptable bas ed on the application. 2947
For example, a power-over-ethernet (PoE) surveillance camera mounted 2948
outdoors supplied by 48 V DC from PoE would be in compliance with Clause 5 2949
if the electrical enclosure met the applicable requirements for outdoor 2950
enclosures. 2951
Fire 2952
It is believed that most aspects relating to protection against fire emanating 2953
from within the equipment are adequately covered by IEC 62368-1. However, 2954
certain measures that may be acceptable for equipment located inside a 2955
building would not be acceptab le outdoors because they would permit the entry 2956
of rain, etc. 2957
For certain types of outdoor equipment, it could be appropriate to allow the 2958
‘no bottom fire enclosure required if mounted on a concrete base’ exemption 2959
that presently can be used for equipment for use within a restricted access 2960
location. 2961
IEC TR 62368-2:2019 © IEC 2019 – 167 –
Mechanical hazards 2962
It is believed that all aspects relating to protection against mechanical hazards 2963
emanating from the equipment are adequately covered by IEC 62368-1. 2964
Heat-related hazards 2965
It is believed that most aspects relating to protection against direct heat 2966
hazards are adequately covered by IEC 62368-1. However, it may be 2967
appropriate to permit higher limits for equipment that is unlikely to be touched 2968
by passersby (for example, equipment that is only intended to be pole mounted 2969
out of reach). A default nominal ambient temperature range for outdoor 2970
equipment has been proposed. The effects of solar heating have not been 2971
addressed. 2972
In addition to direct thermal hazards, there is a need to consider con sequential 2973
hazards. For instance, some plastics become brittle as they become cold. An 2974
enclosure made from such brittle plastic could expose users to other hazards 2975
(for example, electrical or mechanical) if it were to break. 2976
Radiation 2977
It is believed that most aspects relating to direct protection against radiation 2978
hazards are adequately covered by IEC 62368-1. However, there may be 2979
consequential hazards to consider. Just as polymeric materials can be affected 2980
by low temperatures, they can also become embrittled owing to the effect of UV 2981
radiation. An enclosure made from such brittle plastic could expose users to 2982
other hazards (for example, electrical or mechanical) if it were to break. 2983
Chemical hazards 2984
It is believed that certain types of outdoor equipment need to have measures 2985
relating to chemical hazards originating within, or external to, the equipment. 2986
Exposure to chemicals in the environment (for example, salt used to clear 2987
roads in the winter) can also cause problems. 2988
Biological hazards 2989
These are not presently addressed in IEC 62368-1. As with radiation hazards 2990
and chemical hazards, it is thought that there is not likely to be any direct 2991
biological hazard. However, plastics and some metals can be attacked by fungi 2992
or bacteria and this could result in weakening of protective enclosures. As 2993
stated under 'electric shock', the ingress of plants and animals could result in 2994
damage to insulation. 2995
Explosion hazards 2996
Outdoor equipment may need to be weather-tight, in such cases there is an 2997
increased probability that an explosive atmosphere can build up as a result of: 2998
– hydrogen being produced as a result of charging lead -acid batteries within 2999
the equipment and; 3000
– methane and other ‘duct gasses’ entering the equipment from the outdoors. 3001
Y.3 Resistance to corrosion 3002
Rationale: Enclosures made of the following materials are considered to comply with 3003
XX.1 without test: 3004
(a) Copper, aluminum, or stainless steel; and 3005
(b) Bronze or brass containing at least 80 % copper. 3006
Y.4.6 Securing means 3007
Rationale: Gaskets associated with doors, panels or similar parts subject to periodic 3008
opening is an example of a gasket needing either mechanical securement or 3009
adhesive testing. 3010
3011
– 168 – IEC TR 62368-2:2019 © IEC 2019
___________ 3012
3013
IEC TR 62368-2:2019 © IEC 2019 – 169 –
Annex A 3014
(informative) 3015
3016
Background information related to the use of SPDs 3017
NOTE Since there is ongoing discussion in the committee on the use of SPDs in certain situations, the content of 3018 this Annex is provided for information only. This Annex does not in any way override t he requirements in the 3019 document, nor does it provide examples of universally accepted constructions. 3020
A.1 Industry demand for incorporating SPDs in the equipment 3021
The industry has the demand of providing protection of communication equipment from 3022
overvoltage that may be caused by lightning strike surge effect. There are r eports in Japan 3023
that hundreds of products are damaged by lightening surges every year, including the risk of 3024
fire and/or electrical shock according to the damage to the equipment, especially in the 3025
regions where many thunderstorms are observed. We believe it will be the same in many 3026
other countries by the reason described in the next paragraph where the voltage of the surge 3027
is much higher than expected value for overvoltage category II equipment (1 500 V peak or 3028
2 500 V peak). For the surge protection purpose, the manufacturers have need to introduce 3029
the surge protection devices in the equipment, not only for class I equipment but also for 3030
class II equipment or class III equipment, but facing to the difficulty of designing equipment 3031
because of the limited acceptance in IEC 60950-1, 2nd edition and IEC 62368-1, 1st edition. 3032
If the point of bonding of electrical supply to the equipment is not adjacent to the point of 3033
bonding of telecommunication circuit that is connected to the external circuit of the same 3034
equipment, the surge entered from power line or from communication line causes the high 3035
potential difference on the insulation in the equipment, and cause the insulation/component 3036
breakdown which may cause product out -of-use. In some cases, the damage on the insulation 3037
or safeguard can cause hazardous voltage on the SELV/ES1 and accessible metal, or heat-3038
up of insulation material and fire (see Figure A.1 in this document, with the example of class 3039
II equipment.) 3040
The most effective way to protect equipment from a lightning surge is, as commonly 3041
understood internationally, to have an equipotential bonding system in the building/facility with 3042
a very low in-circuit impedance by the use of main-earth bar concept (see Figure A.2 in this 3043
document). This kind of high-quality earthing provision can be introduced in the 3044
building/facility in the business area , such as computer rooms, or in modern buildings. This 3045
kind of high quality earthing provision may not always be possible in the residential area, in 3046
already-existing buildings and in some countries where the reliably low impedance earth 3047
connection may not be easily obtained from technical (according to the characteristics of land) 3048
or even by practical reasons (because very expensive construction change to the building is 3049
required, or according to the lack of regulatory co -work it is difficult to get the relevant 3050
permission for cabling). We should not disregard the fact that many ICT equipment (including 3051
PCs, fax machines, TVs and printers) are brought to home, school and small business offices 3052
into the existing buildings (see Figure A.3 and Figure A.4 in this document). 3053
If the use of surge suppressors by the means of “a varistor in series with a GDT” is allowed in 3054
the equipment to bridge safeguards for class I equipment and to bridge a double safeguard 3055
or a reinforced safeguard for class II equipment, means can be provided to bypass the 3056
surge current, and to avoid the possibility that the lightening surge breaks the circuit or the 3057
insulation within the equipment (see Figure A.2 in this document). 3058
Thus, there is industry demand for using surge protecting device s (SPDs) in the equipment 3059
independent of whether the product is class I equipment, class II equipment or class III 3060
equipment. 3061
– 170 – IEC TR 62368-2:2019 © IEC 2019
3062
Figure A.1 – Installation has poor earthing and bonding; 3063
equipment damaged (from ITU-T K.66) 3064
3065
Figure A.2 – Installation has poor earthing and bonding; using main earth bar 3066
for protection against lightning strike (f rom ITU-T K.66) 3067
3068
IEC TR 62368-2:2019 © IEC 2019 – 171 –
3069
Figure A.3 – Installation with poor earthing and bonding, using a varistor 3070
and a GDT for protection against a lightning strike 3071
3072
Figure A.4 – Installation with poor earthing and bonding; equipment damaged (TV set) 3073
A.2 Technical environment of relevant component standards 3074
Before the publication of IEC 62368-1:2010, there was no appropriate component document 3075
for a GDT deemed to be providing a sufficient level of endurance to be accepted as a 3076
safeguard for a primary circuit. For this reason, a GDT could not be accepted as a reliable 3077
component for use as a safeguard between a primary and secondary circuit. 3078
However, recently IEC SC 37B has been developed new documents for GDTs. In these 3079
documents the spark over voltage of GDT’s has been extended up to 4 500 V DC, taking the 3080
use of GDTs in the mains circuit in to account. We believe therefore that a GDT may be used 3081
as a safeguard if it complies with the following documents: 3082
– IEC 61643-311:2013: Components for low-voltage surge protective devices – Part 311: 3083
Performance requirements and test circuits for gas discharge tubes (GDT) ; 3084
– IEC 61643-312:2013: Components for low-voltage surge protective devices – Part 312: 3085
Selection and application principles for gas discharge tubes ; 3086
The sentence “does not deal with GDTs connected in series with voltage -dependent resistors 3087
in order to limit follow-on currents in electrical power systems; ” in the scope of these 3088
– 172 – IEC TR 62368-2:2019 © IEC 2019
documents with a purpose for expressing that GDTs connected in series with varistors are a 3089
kind of SPD and this issue should be in IEC 61643-11 for SDP’s standard. But this sentence 3090
may be misread as “a GDT is not allowed to be used for primary circuits”, so SC37B decided 3091
to delete the sentence. This decision was made during the IEC SC 37B meeting at Phoenix, 3092
U.S.A, in Oct, 2010. 3093
A.3 Technical discussion 3094
A.3.1 General 3095
For the use as surge protective devices (SPD), there are many types of components and the 3096
combined use of them. Some of them are relatively large in size and useful only in the outdoor 3097
facility or in the building circuits. Some are reliable but others may not. 3098
For use with equipment in the scope of IEC 62368-1, varistors and GDT’s are very commonly 3099
available with appropriate physical size and reliability. 3100
3101
Figure A.5 – Safeguards 3102
A.3.2 Recommended SPD and its level of sparkover voltage 3103
The recommended construction of SPD for the purpose of protecting human and the 3104
insulations in the equipment is the combined use of a GDT and a varistor in series, by the 3105
reasons described in this subclause and A.3.3. 3106
The level of sparkover voltage of the SPD constructed as recommended as above is important 3107
and should be selected as higher than withstand voltage level of insulation which SPD is 3108
intended to protect from damage by surge overvoltage. IEC 61643-311 and IEC 61643-312 3109
provides the selection of GDT ’s up to 4 500V DC sparkover voltage series (see “A” in 3110
Figure A.5 in this document). 3111
A.3.3 Consideration of a GDT and its follow current 3112
If you are going to use a GDT in the primary circuit , or in the external circuit, you have to 3113
take the follow current in GDT into account. For more information on the GDT’s follow current, 3114
see Clause A.4 in this document. 3115
D
IEC TR 62368-2:2019 © IEC 2019 – 173 –
The follow current in the GDT after the surge transient voltage/current that flows through it 3116
may keep the GDT in the low impedance mode while the equipment power is on, resulting in 3117
a risk of electric shock if somebody touches the circuit connected to the GDT. The combined 3118
use of a GDT and a varistor in series is the common method to avoid this risk. Aft er the 3119
transient overvoltage condition is over, the varistor will stop the GDT ’s follow current. 3120
Complying with Clause G.8 is required for the varistor ’s working voltage. It means that 1,25 3121
x Vac is required for the varistor’s working voltage. After the transient, the varistor will stop 3122
the current from the AC line immediately. 3123
For the reliability of the GDT, it is required that the GDT meets the requirements for electric 3124
strength and the external clearance and creepage distance requirements for reinforced 3125
insulation (see “B” in Figure A.5). 3126
A.3.4 Consideration of varistors and its leak current 3127
If a varistor is used in the primary circuit or in the external circuit, the leakage current in the 3128
varistor has to be taken into account. The continuous current caused by the leakage current 3129
may burn the varistor or other components in the circuit, and is energy inefficient. The 3130
combined use of a GDT and a varistor in series is the common method to avoid this effect, 3131
since the GDT can kill the leakage current just after the surge transient voltage passed 3132
through these components. 3133
For the reliability of the varistor, it has to comply with Clause G.8 (see “C” in Figure A.5 in this 3134
document). 3135
A.3.5 Surge voltage/current from mains 3136
A.3.5.1 Case of transversal transient on primary circuit 3137
A surge caused by lightning may enter in the mains circuit and get into the equipment as a 3138
transversal transient overvoltage. In this case, incorporating an SPD (that may be a varistor 3139
only) between the line and neutral of the primary circuit is an effective method to prevent 3140
damage in the circuit, as the surge is bypassed from line to neutral or vice versa. In this case, 3141
the reliability requirement may not be mandatory for the SPD, because the failure of th e SPD 3142
can lead to an equipment fault condition (out of use) but may not lead to risk to human (see 3143
“D” in Figure A.5 in this document). 3144
A.3.5.2 Case of longitudinal transient on primary circuit 3145
A surge caused by lightning may enter in the mains circuit and get into the equipment as a 3146
longitudinal (common mode) transient overvoltage, which may cause high-level potential 3147
difference between the primary circuit and the external circuits in the equipment. In this case, 3148
providing a bypass circuit from the primary circuit to the reliable bonding, or a bypass circuit 3149
between the primary circuit and the external circuits, or both, incorporating an SPD (a 3150
combined use of a GDT and a varistor in series is recommended) is an effective method to 3151
prevent insulations and components in the equipment from being damaged (see “E” in 3152
Figure A.5 in this document). 3153
For preventing the risk of electrical shock in this case, a bypass circuit connected to the SPD 3154
shall be either connected to the earth, or provided with a suitable safeguard from ES1. (A 3155
double safeguard or a reinforced safeguard between the primary side of an SPD and ES1, 3156
and a basic safeguard between external circuit side of SPD and ES1, see “J” and “G” in 3157
Figure A.5 in this document). 3158
There may be a discussion about the safety of the telecommunication network connected to 3159
the external circuit, but it is presumed that the telecommunication network is appropriately 3160
bonded to the earth through the grounding system. Also, the maintenance person accessing 3161
the telecommunication for maintenance is considered to be a skilled person, and knows that 3162
they should not access the network lines when lightning strikes are observed in the nearby 3163
area (see “F” in Figure A.5 in this document). 3164
– 174 – IEC TR 62368-2:2019 © IEC 2019
For the risk that the connection of the external circuit to the telecommunication network is 3165
disconnected, the SPD cannot operate. However, in this case, the external circuit is left 3166
open circuit, therefore the telecom side shall have a safeguard to ES1. Under this condition, 3167
the SPD can be the open circuit (see “G” and “F” in Figure A.5 in this document). 3168
A.3.6 Surge voltage/current from external circuits 3169
A.3.6.1 Case of transversal transient on external circuits 3170
A surge caused by lightning may enter from the external circuit (such as the 3171
telecommunication network) as a transversal transient overvoltage. In this case, incorporating 3172
an SPD (may be a GDT only) between the Tip and Ring of the external circuit is the effective 3173
method to prevent damage in the circuit, as the surge is bypassed from one wire of the 3174
external circuit to another wire. In this case, the reliability requirement is not mandatory for 3175
the SPD, because the failure of the SPD can only lead to an equipment fault condition (out of 3176
use) but may not lead to risk to a person (see “H” in Figure A.5 in this document). 3177
A.3.6.2 Case of longitudinal transient on external circuits 3178
A surge caused by lightning may enter the telecommunication network and get into the 3179
external circuit of the equipment as longitudinal (common mode) transient overvoltage, 3180
which may cause high level potential difference between a mains circuit and external 3181
circuits. In this case, providing a bypass circuit between the primary circuit and external 3182
circuits, or between external circuit and bonding, or both, incorporating an SPD (a 3183
combined use of a GDT and a varistor in series is recommended) is an effective method to 3184
protect insulations and components in the equipment (see “I” in Figure A.5 in this document). 3185
For limiting the risk of electrical shock in this case, a bypass circuit connected to the SPD 3186
shall be either connected to the earth, or provided w ith suitable safeguard from ES1 (A 3187
double safeguard or a reinforced safeguard between the primary side of the SPD and ES1, 3188
and a basic safeguard between the external circuit side of the SPD and ES1, see “J” in 3189
Figure A.5 in this document). 3190
About the consideration of some countries that have no polarity of the AC plug, SPDs 3191
installed between power lines in accordance with IEC 60364 will operate and the surge will go 3192
into the AC line (see “I” in Figure A.5 in this document). 3193
A.3.7 Summary 3194
As a summary of the above technical discussions, the following are proposed requirements if 3195
a varistor is connected in series with a GDT and used as safeguard: 3196
– the GDT’s sparkover voltage level should be selected from IEC 61643-311 and IEC 61643-3197
312 in accordance with the bridged insulation (see A.3.2 in this document); 3198
– the GDT shall pass the electric strength test and meet the external clearance and 3199
creepage distance requirements for reinforced insulation (see A.3.3 in this document); 3200
– the varistor shall comply with Clause G.8 (see A.3.3 and A.3.4 in this document); 3201
– the bypass circuit connected to the SPD shall be either connected to earth, or provided 3202
with a suitable safeguard from ES1 (a double safeguard or a reinforced safeguard 3203
between the primary side of the SPD and ES1, and a basic safeguard between the 3204
external circuit side of the SPD and ES1, see A.3.5.2 and A.3.6.2 in this document). 3205
A.4 Information about follow current (or follow-on current) 3206
A.4.1 General 3207
The information was taken from “MITSUBISHI Materials home page” 3208
IEC TR 62368-2:2019 © IEC 2019 – 175 –
A.4.2 What is follow-on-current? 3209
Follow-on-current is literally something that will continue to flow. In this case it is the 3210
phenomenon where the current in a discharge tube continues to flow. 3211
Normally surge absorbers are in a state of high impedance. When a surge enters the absorber 3212
it will drop to a low impedance stage, a llowing the surge to bypass the electronic circuit it is 3213
protecting. After the surge has passed, the absorber should return to a high impedance 3214
condition. 3215
However, when the absorber is in a low impedance state and if there is sufficient voltage on 3216
the line to keep the current flowing even when the surge ends , the absorber remains in a 3217
discharge state and does not return to a high impedance state. The current will then continue 3218
to flow. This is the phenomenon known as follow-on-current. 3219
Surge absorbers that display this follow-on-current phenomenon are of the discharge type or 3220
semiconductor switching absorbers. A characteristic of these absorbers is that during surge 3221
absorption (bypass) the operating voltage (remaining voltage) is lower than the starting 3222
voltage. 3223
The advantage of this is that during suppression the voltage is held very low, so as to reduce 3224
stress on the equipment being protected. But there can be a problem when the line current of 3225
the equipment is sufficient so that it continues to drive the absorber when the voltage is at a 3226
low state. 3227
Below are more details about the follow-on-current mechanism. The discharge and power 3228
source characteristics for the discharge tube as well as conditions of follow -on-current will be 3229
explained. 3230
A.4.3 What are the V-I properties of discharge tubes? 3231
The micro-gap type surge absorber is one kind of discharge tube. The discharge 3232
characteristics where the part passes through pre -discharge, glow discharge and then arc 3233
discharge are shown in Figure A.6 in this document. 3234
Figure A.6 in this document shows the V-I characteristics relation between voltage and 3235
current for the discharge tube. When the tube discharges, electric current flows and if moves 3236
to a glow discharge state and then an arc state all while the discharge voltage decreases. 3237
Conversely, as the discharge decreases, the voltage increases as it moves from an arc state 3238
to a glow state. 3239
– 176 – IEC TR 62368-2:2019 © IEC 2019
3240
Figure A.6 – Discharge stages 3241
Pre-glow discharge 3242
The voltage that is maintaining this discharge is approximately equal to the DC breakdown 3243
voltage of the part. A faint light can be seen from the part at this point . 3244
Glow discharge 3245
There is a constant voltage rate versus the changing current. The voltage maintai ning this 3246
discharge will depend on the electrode material and the gas in the tube. The discharge light 3247
now covers one of the electrodes. 3248
Arc discharge 3249
With this discharge, a large current flows through the part and it puts out a bright light. The 3250
maintaining voltage at this point (voltage between the discharge tube terminals) is in the 10’s 3251
of volts range. 3252
A.4.4 What is holdover? 3253
When a discharge tube is used on a circuit that has a DC voltage component, there is a 3254
phenomenon where the discharge state in the tube continues to be driven by the current from 3255
the power supply even after the surge voltage has subsided. This is called holdover (see 3256
Figure A.7 in this document). 3257
When holdover occurs, for example, in the drive circuit of a CRT, the screen darkens and 3258
discharge in the absorber continues, which can lead to the glass tube melting, smoking or 3259
burning. 3260
IEC TR 62368-2:2019 © IEC 2019 – 177 –
Figure A.7 – Holdover 3261
Holdover can occur when the current can be supplied to the discharge tube due to varying 3262
conditions of output voltage and output resistance of the DC power supply. What are then the 3263
conditions that allow current to continue to flow to the discharge tube? 3264
The relation between the power supply voltage ( V0), serial resistance (R), discharge current (I) 3265
and the terminal voltage (v) are shown in the linear relation below: 3266
v = V0 – I x R 3267
If the voltage V0 is fixed, the slope of the power supply output characteristic line increases or 3268
decreases according to the resistance and may or may not intersect with the V-I 3269
characteristics of the discharge tube. 3270
The characteristic linear line of a power supply shows the relation between the output voltage 3271
and current of the power supply. Likewise, the V -I curve of a discharge tube shows the 3272
relation between the voltage and current. 3273
When static surge electricity is applied to the discharge tube, the shape of the curve shows 3274
that the surge is being absorbed during arc discharge. 3275
As the surge ends, the discharge goes from arc discharge to glow discharge and then to the 3276
state just prior to glow discharge. At this time the relationship between the discharge tubes 3277
V-I curve and the power supply’s output characteristics are very important. 3278
As shown in the figure, with a high resistance in the power supply, the o utput characteristic 3279
line (pink) and the discharge tubes V-I characteristic curve (red) never intersect. Therefore, 3280
current will not flow from the power supply and follow -on-current will not occur. 3281
However, when the output characteristic line of the power supply (pink) intersects with the V-I 3282
curve of the discharge tube (red), it is possible for current from the power supply to flow into 3283
the discharge tube. When the surge ends, the current should decrease from arc discharge to 3284
the pre-glow state, but instead the power supply will continue to drive the current where it 3285
intersects in the glow or arc discharge region. This is called holdover, and is the condition 3286
where the power supply continues to supply current to the discharge tube at the intersection 3287
on its characteristic line and the discharge tubes V -I curve. 3288
Figure A.8 in this document shows where the power supply can continue supplying curren t to 3289
the discharge tube when its characteristic line intersects the discharge tubes V -I line in the 3290
glow or arc discharge sections. 3291
– 178 – IEC TR 62368-2:2019 © IEC 2019
Figure A.8 – Discharge 3292
To prevent holdover from occurring, it is important to keep the V -I characteristic line of the 3293
power supply from intersecting with the V-I curve of the discharge tube. 3294
A.4.5 Follow-on-current from AC sources? 3295
When using the discharge tube for AC sources, when follow-on-current occurs as per the case 3296
with DC it is easy to understand. 3297
That is, as can be seen in the figure below, the only difference is that the power supply 3298
voltage (V0) changes with time. 3299
As shown on the previous page, when the power supply voltage is shown as V0(t), the output 3300
power characteristics are displayed as follows: 3301
v = V0(t) – R x I 3302
where 3303
v is the the voltage at the power out terminal 3304
I is the current of the circuit 3305
V0(t) will vary with time, so when displaying the above equation on a graph, it will appear as in 3306
Figure A.9 in this document on the left. Then when V0 (t) is shown as: 3307
V0(t) = V0 sin wt 3308
When the power supply voltage becomes 0 (zero cross), there is a short time around this 3309
crossing where the voltage range and time range of the power supply output and discharge 3310
tube V-I curve do not intersect. 3311
For an AC power supply, because there is always a zero crossing of the supply’s voltage, 3312
more than holdover it is easier to stop the discharge. In the vicinity of the zero crossing, it is 3313
impossible to maintain the discharge since the current to the discharge is cut off. The 3314
discharge is then halted by the fact that the gas molecules, which were ionized during this 3315
time, return to their normal state. 3316
Because the terminal voltage does not exceed the direct current break down voltage, if the 3317
discharge is halted it will not be able to start again. 3318
However, if the gas molecules remain ionized during this period and voltage is again applied 3319
to both terminals of the discharge tube (enters the cycle of opposite voltage), this newly 3320
IEC TR 62368-2:2019 © IEC 2019 – 179 –
applied voltage will not allow the discharge to end and it will continue in the discha rge mode. 3321
This is follow-on-current for alternating current. 3322
When follow-on-current occurs, the tube stays in a discharge mode and the glass of the tube 3323
will begin to smoke, melt and possibly ignite. 3324
3325
3326
Figure A.9 – Characteristics 3327
It is important to insert a resistance in series that is sufficiently large to prevent follow -on-3328
current from occurring according to the conditions of the alternating current. 3329
– 180 – IEC TR 62368-2:2019 © IEC 2019
Picture 1: with 0 Ω (follow-on current occurs)
Picture 2: with 0,5 Ω (follow-on current is stopped within half a wave)
3330
Figure A.10 – Follow on current pictures 3331
With 1 Ω and 3 Ω resistance, results are the same as those in picture 2, follow-on-current is 3332
disrupted and discharge stops (see Figure A.10 in this document). 3333
For AC power sources, the resistance value that is connected in series with the discharge 3334
tube is small in comparison to DC sources. 3335
If the series resistance is 0,5 Ω or greater it should be sufficient, however for safety a value of 3336
3 Ω (for 100 V) or greater is recommended. 3337
In addition there is also a method to use a varistor in series that acts as a resistor. In this 3338
case the varistor should have an operating voltage greater than the AC voltage and be placed 3339
in series with the discharge tube. Unlike the resistor, discharge will be stopped without follow -3340
on-current occurring during the first half wave. 3341
Recommended varistor values are: 3342
– for 100 VAC lines: a varistor voltage of 220 V minimum; 3343
– for 200 VAC lines: a varistor voltage of 470 V minimum. 3344
IEC TR 62368-2:2019 © IEC 2019 – 181 –
A.4.6 Applications with a high risk of follow-on-current 3345
1) Holdover: CRT circuits and circuits using DC power supplies 3346
2) Follow-on-current: Circuits using AC power source 3347
3348
– 182 – IEC TR 62368-2:2019 © IEC 2019
Annex B 3349
(informative) 3350
3351
Background information related to measurement of discharges – 3352
Determining the R-C discharge time constant for X- and Y-capacitors 3353
B.1 General 3354
Since the introduction of 2.1.1.7, “Discharge of capacitors in equipment,” in IEC 60950-1:2013, 3355
questions continually arise as to how to measure the R-C discharge time constant. The 3356
objective of this article is to describe how to measure and determine the discharge time 3357
constant. 3358
B.2 EMC filters 3359
EMC filters in equipment are circuits comprised of inductors and capacitors arra nged so as to 3360
limit the emission of RF energy from the equipment into the mains supply line. In EMC filters, 3361
capacitors connected between the supply conductors ( for example, between L1 and L2) of the 3362
mains are designated as X capacitors. Capacitors connect ed between a supply conductor 3363
and the PE (protective earthing or grounding) conductor are designated as Y capacitors 3364
(Safety requirements for X and Y capacitors are specified in IEC 60384-14 and similar 3365
national standards). The circuit of a typical EMC fil ter is shown in Figure B.1. CX is the X 3366
capacitor, and CY are the Y capacitors. 3367
3368
Figure B.1 – Typical EMC filter schematic 3369
B.3 The safety issue and solution 3370
When an EMC filter is disconnected from the mains supply line, both the X (Cx) and the Y 3371
(CYa and CYb) capacitors remain charged to the value of the mains supply voltage at the 3372
instant of disconnection. 3373
Due to the nature of sinusoidal waveforms, more than 66 % of the time (30° to 150° and 210° 3374
to 330° of each cycle) the voltage is more than 50 % of the peak voltage. For 230 V mains 3375
(325 Vpeak), the voltage is more than 162 V for more than 66 % of the time of each cycle. So, 3376
the probability of the voltage exceeding 162 V at the time of disconnection is 0 ,66. This 3377
IEC TR 62368-2:2019 © IEC 2019 – 183 –
probability represents a good chance that the charge on the X a nd Y capacitors will exceed 3378
162 V. 3379
If a hand or other body part should touch both pins (L1 and L2) of the mains supply plug at 3380
the same time, the capacitors will discharge through that body part. If the total capacitance 3381
exceeds about 0,1 µF, the discharge will be quite painful. 3382
To safeguard against such a painful experience, safety documents require that the capacitors 3383
be discharged to a non-painful voltage in a short period of time. T he short period of time is 3384
taken as the time from the disconnection from the mains to the time when contact with both 3385
pins is likely. Usually, this time is in the range of 1 s to 10 s, depending on the documents and 3386
the type of attachment plug cap installed. 3387
B.4 The requirement 3388
The time constant is measured with an oscilloscope. The time constant and its parameters are 3389
defined elsewhere. 3390
The significant parameters specified in the requirement are the capacitance exceeding 0,1 µF 3391
and the time constant of 1 s or less (for pluggable equipment type A) or 10 s or less (for 3392
pluggable equipment type B). These values bound the measurement. This attachment 3393
addresses pluggable equipment type A and the 1 s time constant requirement. The 3394
attachment applies to pluggable equipment type B and the time constant is changed to 10 s . 3395
Pluggable equipment type A is intended for connection to a mains supply via a non-3396
industrial plug and socket-outlet. Pluggable equipment type B is intended for connection to 3397
a mains supply via an industrial plug and socket-outlet. 3398
The document presumes that measurements made with an instrument having an input 3399
resistance of 95 M to 105 M and up to 25 pF in parallel with the impedance and 3400
capacitance of the equipment under test (EUT) will have negligibl e effect on the measured 3401
time constant. The effect of probe parameters on the determination of the time constant is 3402
discussed elsewhere in this document. 3403
The requirement specifies a time constant rather than a discharge down to a specified voltage 3404
within a specified time interval . If the document required a discharge to a specific voltage, 3405
then the start of the measurement would need to be at the peak of the voltage. This would 3406
mean that the switch (see Figure B.5) would need to be opened almost exactly at the peak of 3407
the voltage waveform. This would require special switching equipment. The time constant is 3408
specified because it can be measured from any point on the waveform (except zero), see 3409
Figure B.4b. 3410
B.5 100 M probes 3411
Table B.1 in this document is a list of readily available oscilloscope probes with 100 M input 3412
resistance and their rated input capacitances (the list is not exhaustive). Also included is a 3413
400 M input resistance probe and a 50 M input resistance probe. 3414
– 184 – IEC TR 62368-2:2019 © IEC 2019
Table B.1 – 100 M oscilloscope probes 3415
Manufacturer Input resistance
M
Input capacitance
pF
A 100 1
B 100 6,5
C 100 3
D 400 10 – 13
E 100 2,5
F 50 5,5
3416
Note that the input capacitances of the 100 M probe input capacitances are very much less 3417
than the maximum capacitance of 25 pFs. This attachment will discuss the effect of the probe 3418
capacitance and the maximum capacitance elsewhere. 3419
100 M probes are meant for measuring high voltages, typically 15 kV and more. These 3420
probes are quite large and are awkward to connect to the pins of a power plug. 3421
3422
Figure B.2 – 100 M oscilloscope probes
General purpose oscilloscope probes have 10 M input resistance and 10 pF to 15 pF input 3423
capacitance. General-purpose probes are easier to connect to the pins of the power plug. This 3424
attachment shows that a 10 M, 15 pF probe can be used in place of a 100 M probe. 3425
B.6 The R-C time constant and its parameters 3426
Capacitor charge or discharge time can be expressed by the R -C time constant parameter. 3427
One time constant is the time duration for the voltage on the capacitor to change 63 %. In five 3428
time constants, the capacitor is discharged to almost zero . 3429
IEC TR 62368-2:2019 © IEC 2019 – 185 –
Table B.2 – Capacitor discharge 3430
Time constant Percent capacitor voltage (or
charge)
Capacitor voltage
(230 Vrms
, 331 Vpeak
)
0 100 325
1 37 120
2 14 45
3 5 16
4 2 6
5 0,7 2
3431
The values in Table B.2 in this document are given by: 3432
)(
0RC
t
t eVV−
= 3433
where: 3434
tV is the voltage at time t 3435
0V is the voltage at time 0 3436
R is the resistance, in 3437
C is the capacitance, in F (Farads) 3438
t is the time, in s 3439
The time constant is given by the formula: 3440
EUTEUTEUT CRT = 3441
where: 3442
EUTT is the time, in seconds, for the voltage to change by 63 % 3443
EUTR is the EUT resistance, in 3444
EUTC is the EUT capacitance, in F (Farads) 3445
In the equipment under test (EUT), the EUT capacitance, CEUT, in the line filter (Figure B.1) 3446
includes both the X-capacitor and the Y-capacitors. 3447
The two Y-capacitors, CYa and CYb, are in series. The resultant value of two capacitors in 3448
series, CY, is: 3449
YbYa
YbYa
YCC
CCC
+
= 3450
Assuming the two Y-capacitors have the same value, their L1-L2 value is one-half of the value 3451
of one of the capacitors. 3452
The X-capacitor is in parallel with the two Y-capacitors. The EUT capacitance is: 3453
– 186 – IEC TR 62368-2:2019 © IEC 2019
YXEUT CCC += 3454
The EUT resistance is the resistance, REUT, in the EUT that is used for discharging the 3455
capacitance. 3456
The time constant, TEUT, in s, is the product of the EUT capacitance in farads and the EUT 3457
resistance in . More useful units are capacitance in µF and resistance in M. 3458
Two parameters of the time constant formula are given by the requirement: EUT capacitance 3459
is 0,1 µF or larger and the EUT time constant does not exceed 1 s. Solving the time constant 3460
formula for EUT resistance: 3461
EUTEUTEUT CTR = 3462
Substituting the values: 3463
1 / 0,1EUTR s F= 3464
10 = MREUT 3465
This means that the EUT resistance is no greater than 10 M if the EUT capacitance is 3466
0,1 µF or greater. The combinations of EUT resistance and EUT capacitance for EUT time 3467
constant of 1 s are shown in Figure B.3 in this document. 3468
Figure B.3 – Combinations of EUT resistance and capacitance for 1 s time constant
IEC TR 62368-2:2019 © IEC 2019 – 187 –
B.7 Time constant measurement. 3469
The objective is to measure and determine the EUT time constant. 3470
Measurement of the time constant is done with an oscilloscope connected to th e mains input 3471
terminals of the equipment under test (EUT). Mains is applied to the EUT, the EUT is turned 3472
off, and then the mains is disconnected from the EUT. The EUT is turned off because the 3473
load circuits of the EUT may serve to discharge the EUT capacitance. The resulting 3474
oscilloscope waveform, the AC mains voltage followed by the discharge of the total 3475
capacitance, is shown in Figure B.4 in this document. 3476
– 188 – IEC TR 62368-2:2019 © IEC 2019
a) 240 V mains followed by capacitor discharge V = 50 V/div, H = 1 s /div
3477
b) 240 V mains followed by capacitor discharge V = 50 V/div, H = 0,2 s/div
Figure B.4 – 240 V mains followed by capacitor discharge 3478
The time constant is the time duration measured from the instant of disconnection to a point 3479
that is 37 % of the voltage at the instant of disconnection. 3480
The problem is that the process of measurement affects the measured time constant. This is 3481
because the oscilloscope probe has a finite resistance and capacitance , see Figure B.5 in this 3482
document. 3483
IEC TR 62368-2:2019 © IEC 2019 – 189 –
Figure B.5 – Time constant measurement schematic 3484
The probe resistance, Rprobe, is in parallel to the EUT resistance, REUT. And, the probe 3485
capacitance, Cprobe, is in parallel with the EUT capacitance, CEUT. 3486
The measured time constant, Tmeasured, is a function of the Thevenin equivalent c ircuit 3487
comprised of Rtotal and Ctotal. The measured time constant is given by: 3488
totaltotalmeasured CRT = 3489
where: 3490
measuredT is the measured time for the voltage to change by 63 % 3491
totalR is the total resistance, both the probe and the EUT 3492
totalC is the total capacitance, both the probe and the EUT 3493
Rtotal is: 3494
EUTprobe
EUTprobe
totalRR
RRR
+
= 3495
Ctotal is: 3496
Combining terms, the measured time constant is: 3497
)()( EUTprobe
EUTprobe
EUTprobe
measured CCRR
RRT +
+
= 3498
In this formula, Tmeasured, Rprobe, and Cprobe are known. Tmeasured is measured with a given 3499
probe. Rprobe and Cprobe are determined from the probe specifications (see examples in 3500
– 190 – IEC TR 62368-2:2019 © IEC 2019
Table B.1 in this document). Elsewhere, we shall see that Cprobe is very small and can be 3501
ignored. 3502
EUTtotal CC = 3503
The measured time constant can now be expressed as: 3504
total
EUTprobe
EUTprobe
measured CRR
RRT
+
= )( 3505
B.8 Effect of probe resistance 3506
As has been shown, the EUT discharge resistance, REUT, is 10 M or less in order to achieve 3507
a 1 s time constant with a 0,1 µF capacitor or larger. 3508
Rtotal is comprised of both the EUT discharge resistance REUT, and the probe resistance, 3509
Rprobe. 3510
If REUT is 10 M and CEUT is 0,1 µF, then we know that TEUT is 1 s. If we measure the time 3511
constant with a 100 M probe, the parallel combination of REUT and Rprobe is about 9,1 M 3512
and the measured time constant, Tmeasured, will be: 3513
totaltotalmeasured CRT = 3514
FMTmeasured 1,01,9 = 3515
sTmeasured 91,0= 3516
So, for a CEUT of 0,1 µF capacitance and a REUT of 10 M, a measured time constant (using 3517
a 100 M probe), Tmeasured, of 0,91 s would indicate a EUT time constant, TEUT, of 1 s. 3518
If we substitute a 10 M probe for the same measurement, then Rtotal, the parallel 3519
combination of REUT (10 M) and Rprobe (10 M), is 5 M. The measured time constant, 3520
Tmeasured, will be: 3521
totaltotalmeasured CRT = 3522
FMTmeasured 1,05 = 3523
sTmeasured 5,0= 3524
So, for a CEUT of 0,1 µF capacitance and a REUT of 10 M, the measured time constant 3525
(using a 10 M probe), Tmeasured, is 0,5 s and would indicate a EUT time constant, TEUT, of 1 3526
s. 3527
B.9 Effect of probe capacitance 3528
According to the document, CEUT is 0,1 µF or more. Also, according to the document, Cprobe 3529
is 25 pF or less. Assuming the worst case for Cprobe, the total capacitance is: 3530
IEC TR 62368-2:2019 © IEC 2019 – 191 –
EUTprobetotal CCC += 3531
uFuFCtotal 1,0000025,0 += 3532
uFCtotal 100025,0= 3533
The worst-case probe capacitance is extremely small (0,025 %) compared to the smallest 3534
CEUT capacitance (0,1 µF) and can be ignored. We can say that: 3535
EUTtotal CC = 3536
B.10 Determining the time constant 3537
According to the document, TEUT may not exceed 1 s. 3538
1=EUTT 3539
EUTEUT CR =1 3540
where: 3541
EUTR is 10 M or less 3542
EUTC is 0,1 µF or more 3543
The problem is to determine the values for REUT and CEUT. Once these values are known, the 3544
equipment time constant, TEUT, can be determined by calculation. 3545
As shown in Figure B.1 in this document, REUT can be measured directly with an ohmmeter 3546
applied to the mains input terminals, i.e., between L1 and L2. Care is taken that the 3547
capacitances are fully discharged when the resistance measurement is made. Any residu al 3548
charge will affect the ohmmeter and its reading. Of course, if the circuit is provided with a 3549
discharge resistor, then the capacitances will be fully discharged. If the circuit does not have 3550
a discharge resistor, then the ohmmeter will provide the disch arge path, and the reading will 3551
continuously increase. 3552
CEUT can also be measured directly with a capacitance meter. Depending on the particular 3553
capacitance meter, REUT may prevent accurate measurement of CEUT. For the purposes of 3554
this paper, we assume that the capacitance meter cannot measure the CEUT. In this case, we 3555
measure the time constant and compensate for the probe resistance. 3556
So, the time constant is measured, and the probe resistance is accounted for. 3557
Since probe resistance is more or less standardized, we can calculate curves for 100 M and 3558
10 M probes for all maximum values of REUT and CEUT. The maximum values for 3559
combinations of REUT, CEUT (Ctotal), Rprobe, Rtotal and Tmeasured are given in Table B.3 in this 3560
document. (Rprobe and Rtotal values are rounded to 2 significant digits.) 3561
– 192 – IEC TR 62368-2:2019 © IEC 2019
Table B.3 – Maximum Tmeasured values for combinations of REUT 3562
and CEUT for TEUT of 1 s 3563
TEUT
s
CEUT
(Ctotal
)
µF
REUT
M
Rprobe
M
Rtotal
M
Tmeasured
s
1 0,1 10 100 9,1 0,91
1 0,2 5 100 4,8 0,95
1 0,3 3,3 100 3,2 0,97
1 0,4 2,5 100 2,4 0,97
1 0,5 2 100 2,0 0,98
1 0,6 1,7 100 1,6 0,98
1 0,7 1,4 100 1,4 0,99
1 0,8 1,25 100 1,2 0,99
1 0,9 1,1 100 1,1 0,99
1 1,0 1 100 1,0 0,99
1 0,1 10 10 5,0 0,50
1 0,2 5 10 3,3 0,67
1 0,3 3,3 10 2,5 0,75
1 0,4 2,5 10 2,0 0,80
1 0,5 2 10 1,7 0,83
1 0,6 1,7 10 1,4 0,86
1 0,7 1,4 10 1,25 0,88
1 0,8 1,25 10 1,1 0,89
1 0,9 1,1 10 1,0 0,90
1 1,0 1 10 0,91 0,91
3564
For each value of REUT and Rprobe we can calculate the worst-case measured time constants, 3565
Tmeasured for a TEUT of 1 s. These are shown in Figure B.6 in this document. 3566
The process is: 3567
– With the unit disconnected from the mains and the power switch “off,” measure the 3568
resistance between the poles of the EUT. Repeat with the power switch “on” as the filter 3569
may be on the load side of the power switch. Select the higher value as REUT. 3570
– Connect the oscilloscope probe between L1 and L2 as shown in Figure B.5 in this 3571
document. For safety during this test, use a 1:1 isolating transformer between the mains 3572
and the EUT. Set the scope sweep speed to 0 ,2 ms per division (2 s full screen). 3573
– When the display is about 1 or 2 divisions from the start, turn the test switch off, and 3574
measure the time constant as shown in Figure B.4 in this document. This step may need 3575
to be repeated several times to get a suitable waveform on the oscilloscope. This step 3576
should be performed twice, once with the EUT power switch “o ff” and once with the EUT 3577
power switch “on.” Select the maximum value. This value is Tmeasured. 3578
– Plot REUT and Tmeasured on the chart, Figure B.6 in this document. 3579
If the point is below the curve of the probe that is used to meas ure the time constant, then the 3580
EUT time constant, TEUT, is less than 1 s. 3581
IEC TR 62368-2:2019 © IEC 2019 – 193 –
3582
Figure B.6 – Worst-case measured time constant values for 100 M and 10 M probes 3583
B.11 Conclusion 3584
Measurement of the time constant can be made with any probe, not just a 100 M probe. 3585
Ideally, the probe input resistance should be at least equal to the worst -case EUT discharge 3586
resistance (10 M for pluggable equipment type A) or higher. The effect of the probe input 3587
resistance is given by the equation for Rtotal. 100 M probes, while approaching ideal in terms 3588
of the effect on the measured time constant, are bulky an d expensive and not necessary. 3589
The document is a bit misleading by ignoring a 9 % error when a 100 M probe is used to 3590
measure the time constant associated with a 10 M discharge resistor (see Figure B.5 in this 3591
document). 3592
3593
– 194 – IEC TR 62368-2:2019 © IEC 2019
Annex C 3594
(informative) 3595
3596
Background information related to resistance to candle flame ignition 3597
In line with SMB decision 135/20, endorsing the ACOS/ACEA JTF recommendations, the 3598
former Clause 11 was added to the document up to CDV stage. However, the CDV was 3599
rejected and several national committees indicated that they wanted to have the requirements 3600
removed from the document. At the same time, several countries indicated that they wanted 3601
the requirements to stay, while others commented that they should be limited to CRT 3602
televisions only. 3603
IEC TC 108 decided to publish the requirements as a separate document so that the different 3604
issues can be given appropriate consideration. 3605
3606
3607
IEC TR 62368-2:2019 © IEC 2019 – 195 –
Bibliography 3608
IEC 60065:2014, Audio, video and similar electronic apparatus – Safety requirements 3609
IEC 60215, Safety requirements for radio transmitting equipment – General requirements and 3610
terminology 3611
IEC 60364-4-43, Low-voltage electrical installations – Part 4-43: Protection for safety – 3612
Protection against overcurrent 3613
IEC 60364-5-52, Low-voltage electrical installations – Part 5-52: Selection and erection of 3614
electrical equipment – Wiring systems 3615
IEC 60364-5-54, Low-voltage electrical installat ions – Part 5-54: Selection and erection of 3616
electrical equipment – Earthing arrangements and protective conductors 3617
IEC 60446, Identification by colours or numerals 2 3618
IEC TS 60479-2, Effects of current on human beings and livestock – Part 2: Special aspects 3619
IEC 60664-2 (all parts), Insulation coordination for equipment within low -voltage systems – 3620
Part 2: Application guide 3621
IEC 60664-4:2005, Insulation coordination for equipment within low -voltage systems – Part 4: 3622
Consideration of high-frequency voltage stress 3623
IEC 60695-2 (all parts), Fire hazard testing – Part 2: Glowing/hot-wire based test methods 3624
IEC 60695-2-13, Fire hazard testing – Part 2-13: Glowing/hot-wire based test methods – 3625
Glow-wire ignition temperature (GWIT) test method for materials 3626
IEC 60695-11-2, Fire hazard testing – Part 11-2: Test flames – 1 kW nominal pre-mixed flame 3627
– Apparatus, confirmatory test arrangement and guidance 3628
IEC 60950-1:2005, Information technology equipment – Safety – Part 1: General requirements 3629
IEC 60950-1:2005/AMD1:2009 3630
IEC 60950-1:2005/AMD2:2013 3631
IEC 61010-1, Safety requirements for electrical equipment for measurement, control, and 3632
laboratory use – Part 1: General requirements 3633
IEC 61051-1, Varistors for use in electronic equipment – Part 1: Generic specification 3634
ISO/IEC Guide 51:1999, Safety aspects — Guidelines for their inclusion in standards 3635
ITU-T K.21:2008, Resistibility of telecommunication equipment installed in customer premises 3636
to overvoltages and overcurrents 3637
EN 41003:2008, Particular safety requirements for equipment to be connected to 3638
telecommunication networks and/or a cable distribution system 3639
EN 60065:2002, Audio, video and similar electronic apparatus – Safety requirements 3640
___________
2 This publication was withdrawn.
– 196 – IEC TR 62368-2:2019 © IEC 2019
NFPA 70, National Electrical Code 3641
NFPA 79:2002, Electrical Standard for Industrial Mach inery 3642
UL 1667, UL Standard for Safety Tall Institutional Carts for Use with Audio -, Video-, and 3643
Television-Type Equipment 3644
UL 1995, UL Standard for Safety for Heating and Cooling Equipment 3645
UL 2178, Outline for Marking and Coding Equipment 3646
UL 60065, Audio, Video and Similar Electronic Apparatus – Safety Requirements 3647
UL/CSA 60950-1, Information Technology Equipment – Safety – Part 1: General 3648
Requirements 3649
CAN/CSA C22.1, Information Technology Equipment – Safety – Part 1: General Requirements 3650
CSA C22.1-09, Canadian Electrical Code – Part I: Safety Standard for Electrical Installations 3651
– Twenty-first Edition 3652
ASTM C1057, Standard Practice for Determination of Skin Contact Temperature from Heated 3653
Surfaces Using A Mathematical Model and Thermesthesiometer 3654
EC 98/37/EC Machinery Directive 3655
3656
_____________ 3657
3658