PRODUCT STANDARDS

The objective of product safety standards is to

prescribe a set of construction criteria that will ensure

the safe operation of the electrical device, as well as

to protect the user. A standard is a written document

issued by a countries’ national safety agency or

standards committee. Product standards clearly

specify how an end user’s device is to be built, tested,

and perform safely. Examples of common U.S. and

European product standards are:

UL 1950 “Safety of Information Technology

Equipment”

UL 544 “Medical and Dental Equipment”

EN 60950 “Safety of Information Technology

Equipment”

EN 60601 “Safety of Medical Equipment”

EN 60065 “Safety Requirements for Mains

Operated Electronic & Related Apparatus for

Household and Similar General Use”

Both UL (Underwriters Laboratories) and CSA

(Canadian Standards Association) issue standards as

well as provide product testing services for obtaining

approvals. In European nations, the IEC (International

Electrotechnical Commission) also issues standards

created via a network of international technical

committees. The European Committee for Electric

Standardization (CENELEC) generates documents

called “European Norms” (EN). These documents are

based on existing IEC product standards with any

national deviations noted. It is the responsibility of

each national safety agency to provide testing for

approvals as IEC does not perform any test functions.

Examples of other national safety agencies are:

BSI British Standards Institution (United Kingdom)

IMQ Instituto ltaliano del Marchio di Qualita (Italy)

MITI Ministry of International Trade & Industry (Japan)

SEMKO Svenska Elektriska Materielkontrollanstalten

(Sweden)

VDE Verband Deutscher Elektrotechniker (Germany)

All European member nations of CENELEC are

mandated to accept the use of EN’s. Members include

Austria, Belgium, Czech Republic, Denmark, Finland,

France, Germany, Greece, Iceland, Ireland, Italy,

Luxembourg, the Netherlands, Norway, Portugal,

Sweden, Spain, Switzerland, and the United Kingdom.

COMPONENT STANDARDS

Most product standards usually mention that

individual components such as fuses, be tested and

approved to their own appropriate construction

standard. Component standards are focused on

defining categories, dimensions, electrical ratings, test

set-ups, and reliability criteria. While there are several

standards for fuses from small board-mounted types

to high voltage power line types, the most common

standards for electronic fuses are:

UL 248-14 Low Voltage Fuses-Supplemental

Fuses

CSA-C22.2 No.248.14 L.V. Fuses-Supplemental

Fuses

IEC 60127-2 Miniature (Cartridge) Fuses

IEC 60127-3 Subminiature Fuses

IEC 60127-4 Universal Modular Fuses (UMF)

Please note that the UL and CSA standards are

identical harmonized documents which took effect

October 1st , 1994. The UMF standards (IEC 60127-4)

was published in 1996. Construction standards for

fuse holders are:

UL 512 Fuse holders

CSA C22.2 No.39-M1987 Fuse holder Assemblies

IEC 60127-6 Fuse holders for Miniature Fuses

APPROVALS

An approval, as determined by an independent testing

agency, certifies conformance to an appropriate

standard. Meeting the requirements of a component

standard, however, does not imply automatic agency

approval. Such approvals must be applied for, and are

only granted after satisfactory testing has been

performed. To carry an Approval mark such as that

issued by UL, CSA, VDE or SEMKO, a fuse or holder

must be manufactured to one of the aforementioned

standards. Approvals play a large part in determining

a fuse or holder’s suitability for a given application. A

summary of approvals follows:

UL Listing: This symbol, granted by the U.S.

agency, guarantees that a fuse has been

manufactured in full compliance with the UL 248-14

standard. A fuse carrying a UL Listing cannot qualify

for either a VDE or SEMKO approval for reasons

explained in the next section.

CSA Certification: This symbol, granted by

the Canadian agency, guarantees that a fuse or

holder has been manufactured in full compliance with

the CSA C22.2 No. 248.14 or CSA C22.2 No.39

standard, respectively. A fuse carrying a CSA

Certification cannot qualify for either a VDE or

SEMKO approval for reasons explained in the next

section.

SEMKO Approval: This symbol, granted by

the Swedish agency, guarantees that a fuse or holder

has been manufactured in full compliance with the

appropriate section of the IEC 60127 standard. A fuse

carrying a SEMKO approval cannot qualify for either a

UL Listing or CSA Certification for reasons explained

in the next section.

VDE Approval: This symbol, granted by the

German agency, guarantees that a fuse or holder has

been manufactured in full compliance with the

appropriate section of the IEC 60127 standard. Until

recently, a fuse carrying a VDE approval could not

qualify for either a UL Listing or CSA Certification for

reasons explained in the next section.

BSI Kitemark License: This symbol, granted by the British agency, guarantees that a fuse

has been manufactured in full compliance with the

appropriate section of the IEC 60127 (BS 4265)

standard. A fuse carrying a BSI approval cannot

qualify for either a UL Listing or CSA Certification for

reasons explained in the next section.

Dentori Approval: This symbol,

granted by the Japan Electrical Testing Laboratory,

guarantees that a fuse has been manufactured in full

compliance with the Japanese MITI standard. This

document is similar to UL 248-14 with subtle

differences in voltage ratings and breaking capacity

criteria.

UL Recognition: UL’s Component Recognition Program allows the testing of

components (including fuses and holders) for which

no UL standard exists or where only certain sections

of a particular UL standard are referenced. A fuse or

holder may be submitted to UL for testing according to

criteria defined by the manufacturer. If basic safety

requirements are met during testing and the

component performs as predicted, it can be UL

Recognized. Fuses built to the European IEC 60127

fuse standard (with SEMKO, VDE, and/or BSI

approvals) are technically qualified to apply for UL

Recognition.

c-UL Listing: This approval is similar to CSA Certification. Since UL is accredited by the Standards

Council of Canada as a Certified Organization and

Testing Organization, it can perform component

testing to applicable Canadian standards. This

approval guarantees full compliance with the selected

Canadian component standard and is technically

equivalent to CSA Certification.

c-UL Recognition: This approval is similar

to that offered by the CSA Component Acceptance

Program. If basic Canadian safety requirements are

met during testing and the component performs as the

manufacturer predicts, it can be c-UL Recognized. As

with UL Recognition, “Conditions of Acceptability” are

listed in the test report.

c-UL-us Listing: This approval combines

the UL Listing and c-UL Listing into a single approval

valid for the U.S. and Canada. This approval

guarantees full compliance with the selected

component standards.

c-UL-us Recognition: This approval

combines the UL Recognition and c-UL Recognition

into a single approval valid for the U.S. and Canada.

As with UL Recognition, “Conditions of Acceptability”

are listed in the test report.

UMF Tulip Mark: This symbol is applied to

Universal Modular Fuses (UMF) that have been found

to be compliant with IEC 60127-4. It is now possible to

obtain a true UL Listing and European approvals for a

UMF fuse.

For each fuse and holder approval、we have listed the

applicable our File Number for each safety agency.

These agencies will require this file number during the

product evaluation process. Contact us if approval

certificates are needed or file numbers are not listed.

UL/CSA vs. IEC

There are significant differences between the

requirements listed in the UL 248-14/CSA 248.14

standard and the IEC 60127 fuse standards. Whereas,

both documents have much in common when

describing physical dimensions and materials used in

construction, they completely contradict each other

when defining pre-arcing time vs. current

characteristics of fuses.

This incompatibility alone makes it impossible to build

an electronic fuse that fully complies with all of these

standards. Knowledge of these fundamental

differences will enable the design to properly select an

approved fuse type for any given application. Since

the fuse is one of the last items selected in the design,

this knowledge can be a time-saver during product

approval.

Time vs. Current Characteristics

The rated current (IRated) of an electronic fuse must be

equal to or greater than the continuous operating

current in the circuit where the fuse is used. The

maximum allowable continuous current through a

given fuse type varies as follows:

Standard Voltage Rating Allowable Continuous

Operating Current(23o)

UL/CSA 250V < 75% x IRated

UL/CSA 125V < 70% x IRated

IEC 250V < 100% x IRated

IEC 125V < 70% x IRated

IEC(UMF) 32V-250V < 80% x IRated

Ul & IEC Time-current Curves Figure 1

This means that UL/CSA fuses must be “oversized” by

a minimum of 35%-40% while IEC fuses (rated at

250V) can be used continuously at their full load rating.

The oversizing factor is required to simulate “real

world” conditions as opposed to tightly controlled lab

test conditions. This factor compensates for line

fluctuations, enclosed fuseholders, air movement,

variances in wire and solders track dimensions, and

differences in contact resistances. This difference in

the definition of rated current means that a 1.0 Amp

IEC fuse is approximately equivalent to a 1.4 Amp

UL/CSA fuse. Sizing information is especially critical

during fuse replacement since an incorrect selection

could lead to nuisance trips (undersizing) or potential

fire hazards (oversizing).

Each fuse standard also dictates non-fusing and

fusing timecurrent limits. Non-fusing time defines the

minimum time which a fuse should carry a specified

current without blowing. Fusing time is defined as the

allowable time range (min-max) which a fuse should

carry a specified current before blowing. A summary

of these characteristics is shown on page 6.

Non-fusing times denoted by a “*” is the time at which

temperature stabilization of the melting element

occurs.

Dimensions

The UL/CSA standard does not specify any

dimensions for miniature cartridge fuses, however,

subminiature “microfuses” are required to have no

principal dimension exceeding 10mm. IEC 60127-2

categorizes requirements for miniature fuses with

dimensions of 5x20mm and 6.3x32mm only. IEC

127-3 covers three configurations of subminiature

fuses-similar to the picofuse, MET and MEF types

shown herein. IEC 60127-4 only covers radial-leaded

subminiature fuses and surface mount fuses. Terminal

spacing vary by voltage rating. All dimensions

including body shape and lead spacing are explicitly

listed.

Current Ratings

UL/CSA only suggests typical current ratings up to a

maximum of 60 Amps in the supplemental fuse

category. It is left up to the manufacturer which

increments to build. UL and CSA approvals cover a

range (min-max) of current ratings (ie. 1 A, 2 A, 3.15 A)

that can be built and tested for approvals. The

maximum current rating mentioned in IEC 60127 is

6.3 Amps. This means that fuses with ratings above

6.3 Amps cannot carry any European approvals. They

are referred to as “non-standard ratings.” If a fuse with

a higher current rating (>6.3 Amps) is used in a device,

it may only be eligible for an application-specific

approval. Additional testing may be performed and the

approval itself may have stipulations.

Miniature Fuse Time-Current Characteristics Table 1

UL/CSA 248-14 IEC 60127-2

%Rated

Current

Current

Range

Fast

Acting

Normal

Blow

Time

Delay

Quick

Acting

I

Quick

Acting

II

Time

Lag

III

Time

Lag

V

Time

Lag

VI

100% 0-10A * *

135% 0-10A <1hr. <1hr.

50mA-6.3A >1hr.

32mA-6.3A >1hr. >1hr. >1hr. 150%

1A-6.3A >1hr.

0-10A <2min. 200%

0-3A >5s

50mA-6.3A <30min.

32mA-6.3A <30min. <2min. <2min. 210%

1A-6.3A <30min.

50mA-3.15A 10ms-2s

4A-6.3A 10ms-3s

32mA-100mA 10ms-500ms 200ms-10s 200ms-10s

125mA-6.3A 50ms-2s 600ms-10s 600ms-10s

275%

1A-6.3A 1s-80s

50mA-6.3A 3ms-300ms

32mA-100mA 3ms-100ms 40ms-3s 40ms-3s

125mA-6.3A 10ms-300ms 150ms-3s 150ms-3s

1A-3.15A 95ms-5s

400%

4A-6.3A 150ms-5s

50mA-6.3A <20ms

32mA-6.3A <20ms

32mA-100mA 10ms-300ms 10ms-300ms

125mA-6.3A 20ms-300ms 20ms-300ms

1A-3.15A 10ms-100ms

1000%

4A-6.3A 20ms-100ms

* Fuse shall not open upon reaching stable operating temperature

Subminiature Fuse Time-Current Characteristics Table 2

UL/CSA 248-14 IEC 60127-4(UMF) IEC 60127-3

%Rated

Current

Current

Range

Fast

Acting

Time-Lag

Time-Lag

II

Quick-Acting

III

Time-Lag

IV

100% 0-10A *

125% 32mA-6.3A >1hr.

50mA-5A >1hr. 150%

40mA-4A >1hr.

0-10A <1min.

32mA-6.3A <2min. 200%

50mA-5A <5s

50mA-5A <30min. 210%

40mA-4A <2min.

50mA-5A 10ms-3s 275%

40mA-4A 400ms-10s

50mA-5A <30ms 3ms-300ms 400%

40mA-4A 150ms-3s

32mA-6.3A 10ms-100ms

50mA-5A <20ms 1000%

40mA-4A 20ms-150ms

* Fuse shall not open upon reaching stable operating temperature

Breaking Capacity

Breaking capacity requirements listed in each standard are shown below:

Standard Voltage

(VAC)

Test

Current(A) Fuse Type

UL 32 1000 Blade

UL/CSA 125 50 Micro

UL/CSA 125 10,000 Miniature

UL/CSA 250 35 Mini(0-1A)

UL/CSA 250 100 Mini(1.1-3.5A)

UL/CSA 250 200 Mini(3.6-10A)

UL/CSA 250 750 Mini(10.1-15A)

UL/CSA 250 1500 Mini(15.1-30A)

IEC

60127-2 250 35or10xIRated Mini(Low)

IEC

60127-2 250 150 Mini(Enhanced)

IEC

60127-2 250 1500 Mini(High)

IEC

60127-3 250 35or10xIRated Subminiature

IEC 125 50 Subminiature

60127-3

IEC

60127-4 32,63 35or10xIRated Submini, SM

IEC

60127-4 125 50or10xIRated Submini, SM

IEC

60127-4 250 100 Submini, SM

IEC

60127-4 250 500 Submini, SM

IEC

60127-4 250 1500 Submini, SM

Breaking Capacity Criteria Table 3

Typically, only ceramic body fuses with a 1500 Amp

rating (HBC) are recommended for use in products

directly connected to the AC mains. It is possible,

however, that EBC (enhanced breaking capacity) fuse

types may be substituted in circuits where maximum

short circuit currents are known not to exceed 150

Amps.

Power Factor

Microfuses built to the UL/CSA standard and

subminiature fuses built to the IEC 60127-3 standard

have their breaking capacity tests conducted at a

power factor of 0.95 to 1.0. Test set-ups on UL/CSA

and IEC 60127-2 miniature fuses use a power factor

of 0.7-0.8 with an exception for IEC 60127-2 glass

fuses. Tests on these low breaking capacity types use

a power factor of 1.0. Required power factors in IEC

60127-4 vary by breaking capacity category.

Stress Tests

Endurance testing is required for all IEC 60127

approved fuses. Miniature fuses are subjected to

120% of rated current (100% for MEF fuses) for 100

cycles followed by one hour at 150% of rated current.

Tests on picofuses and MET fuses are conducted at

80% of rated current for 100 hours. After the test, the

fuse must still conduct and have a maximum voltage

drop increase of 10%. All time lag fuses under IEC

60127 are subjected to high ambient operating tests

at 70℃ for one hour. The fuses cannot open during

the test. None of these parameters are tested in the

UL/CSA standard.

Miscellaneous

Maximum voltage drops and power dissipation values

are specified for all current ratings in the IEC 60127

standard. Neither of these parameters are required in

the UL/CSA standard.

Universal Modular Fuse-links (IEC 60127-4)

In an effort to recognize the efforts of manufacturers to

build products for a global marketplace, a single fuse

standard acceptable to both North American and

European safety agencies was published in 1996.

This document enables a single fuse type to obtain

worldwide approvals such as UL and VDE. Specific

dimensions, printed circuit board layouts and electrical

rating are specified. Voltage rating increments are 32V,

63V, 125V, and 250V. Solderability testing of

terminations (leads and SM pads) is also required.

Note that time vs. current characteristics are tested at

125%, 200% and 1000% of rated current adding more

confusion to proper selection. Presently, OUR offers

one surface mount Chip Fuse (No.446) that complies

with IEC 60127-4.

The CE symbol is only an identification of

the conformity of guidelines in connection with the

technical harmonization within the European

Community. This means that the CE symbol is not a

quality or standard conformity approval, but an

administrative symbol. OUR products comply with the

Low Voltage Directives 73/23/EWG. This is valid for

components with an operating voltage or rated voltage

between 50VAC and 1000VAC or 75VDC and

1500VDC. The CE symbol, according to the Directive,

will be shown on the fuse or holder shipping box only.

QUALITY ASSURANCE

All of OUR manufacturing plants worldwide have

applied for and received the Certificate of Registration

designating OUR as an ISO 9001 manufacturer. The

manufacture of high quality circuit protection

components necessitates extensive knowledge and

experience over many yeas. The ISO 9000 Series is

an internationally recognized family of standards

considered to be the premier benchmark of quality

assurance systems. “ISO Certified” means that the

processes used by a company to accept a purchase

order, review it’s requirements, process internal

paperwork and to design, produce, test, and deliver

the product, meet or exceed the requirements of the

DIN ISO 9001 standard as determined by an

independent auditor. For a copy of our current ISO

Certificate, please contact us.

Vendor materials are sample tested in accordance

with IEC 410 (MIL STD 105D, ISO 2859). During the

production process, statistical process controls (SPC)

and in-line process controls are utilized. Upon

completion of the manufacturing process, all fuses

undergo a 100% cold resistance test. The final test of

manufactured parts is Test Level II with an Acceptable

Quality Level (AQL) value of 0.25 or 0.4 in accordance

with IEC 2859 T1, whereby we distinguish between:

Critical Faults – present danger to body or life which

exclude use for safety reasons (i.e. not blowing within

the prescribed time-current limits).

Main Faults – that which limits application of fuse (i.e.

improperly marked or dimensions exceeding

tolerance levels).

Secondary Faults – that which impairs appearance

but does not affect normal operation.

The time vs. current characteristic test is carried out

according to Test Level S4 with a total AQL value of

0.65. Because this is a destructive test, it is based on

an extreme value observation. Non-fusing tests are

performed on fuses with high cold resistance values

while fusing tests are conducted on fuses with low

cold resistance values. Test certificates by

commission and lot number are available for fuses

that ship in industrial size containers.

MANUFACTURER RESPONSIBILITY

With regard to product safety of the device and

reliability of the fuse-link, a correct selection is

important. Only when choosing correctly and when

using as agreed under consideration of the safety

principle (ie. human beings, animals, and intrinsic

values must be protected against danger) can a

definite function of the fuse as a protective component

be possible. Please refer to VDE 0022 Section 2.3.5 –

Self responsibility of the manufacturer of electrical

devices which states: “Any person involved in the

production of electrical plant systems or the

manufacture of electrical equipment including those

dealing with the operation of such systems or

equipment, is in accordance with present

interpretation of the law, individually responsible for

every aspect of compliance to the recognized rules

and procedures of electrical engineering.

Standards & Testing Agencies

Agency Address Contact

BELLCORE Telcordia Technologies 8 Corporate Place

Piscataway, NJ 08854 USA

TEL: +1/ (732) 699-5800 FAX: +1/ (732) 336-2559

WEB: http://www.telcordia.com

BSI

British Standards Institution Quality Assurance

Services PO Box 375 Milton Keynes MK 14 6ll

England

TEL: +44/ 1 908 22 09 08 FAX: +44/ 1 908 22 06 71

WEB: http://www.bsi.org.uk

CCC CEPREI Box 1501 510610 Guangzhou China TEL: +86/ 20 8723 7006 FAX: +86/ 20 8723 6171

CSA Canadian Standards Association 178 Rexdale

Boulevard Toronto, Ontario M9W 1R3 Canada

TEL: +1/ (416) 747-4000 FAX: +1/ (416) 747-4149 WEB: http://www.csa.ca

DIN Deutsches Institute fur Normung Burggrafenstrasse 6

Postfach 11 Q7 D-10787 Berlin Germany

TEL: +49/ 30 26 011 FAX: +49/ 30 26 011263 WEB: http://www.din.de

FCC Federal Communication Commission 1919 M Street

NW Washington, DC 20554 USA

TEL: +1/ (202) 418-0200 FAX: +1/ (202) 418-2825 WEB: http://www.fcc.gov

IEC International Electrotechnical Commission 3,Rue de

Varembe CH-1211 Geneva 20 Switzerland

TEL: +41/ 22 919 0211 FAX: +41/ 22 919 0300 WEB: http://www.iec.ch

ITU International Telecommunications Union Place des

Nations CH-1211 Geneva 20 Switzerland TEL: +41/ 22 730 5111 WEB: http://www.itu.ch

ISO

International Standards Organization 1, Rue de

Varembe Case Postale 56 CH-1211 Geneva 20

Switzerland

TEL: +41/ 22 749 0111 FAX: +41/ 22 733 3430 WEB: http://www.iso.ch

MITI

Japanese Industrial Standards Office Agency of

Industrial Science & Technology 1-3-1 Kasumigaseki

1-Chome Chiyoda-ku, Tokyo 100

TEL: +81/ 3 501 9296 FAX: +81/ 3 580 1418

WEB: http://www.miti.go.jp/index-e.html

SEMKO Svenska Elektriska Materielkontrollanstalten Box

1103 16422 Kista Sweden

TEL: +46/ 8 750 00 00 FAX: +46/ 8 750 60 30

WEB: http://www.semko.se

TÜV RW- TÜV Anlagenteknik GmbH Abt. 7. 1 Steubenstr.

53 D-45138 Essen Germany

TEL: +49/ 201 825 3413 FAX: +49/ 201 825 3209

WEB: http://www.tuev.rwtuv.de

UL Underwriters Laboratories, Inc. 333 Pfingsten road

Northbrook, IL 60062 USA

TEL: +1/ (708) 272-8800 FAX: +1/ (708) 272-8129 WEB: http://www.ul.com

VDE Verband Deutscher Electrotechnicker Merianstrasse

28 D-63069 Offenbach am Main Germany

TEL: +49/ 69 8306 0 FAX: +49/ 69 8306 555 WEB: http://www.vde.de

FUSE PURPOSE

Fuse links protect electrical devices and components

from overcurrents and short circuits. This is achieved

automatically by the melting of a fuse wire through

which a fault current flows. An irreversible, physical

separation is created thereby cutting off current flow

through that conductor. Fuse links are rated so as to

reliably interrupt current flow when it reaches a

predictable magnitude for a fixed duration. For all

practical purposes, a fuse is invisible to the circuit.

An optimum matching of fuse characteristics to the

protective requirements of any device is important to

provide both adequate protection of the end-user and

maximum utilization of other circuit components. In

order to minimize consequential damage and to

comply with the requirements and standards of

modern electrotechnology, we have compiled in the

following paragraphs essential selection and

application criteria for electronic fuses.

VOLTAGE RATING

Standards establish voltage ratings for various types

of fuses. A fuse may be operated at any voltage level

below its voltage rating. These ratings indicate that a

fuse will reliably interrupt fault currents in a circuit

where the operating voltage is equal to, or less than

the rated voltage of the fuse. Since fuses are only

sensitive to changes in circuit current, it is not until the

fuse wire actually melts, that the rated voltage and

available power becomes an issue. It is important that

fuse construction prohibits an open circuit voltage

from causing an arc “restrike” across open fuse

terminals. Standards either require that a fault voltage

remain applied for 30 seconds subsequent to

interruption of current flow without an arc restrike

occurring, or that the insulation resistance across the

blown fuse measures at least 0.1 MOhm. For this

reason, the rated voltage of the fuse must be at least

equal to or greater than the operating voltage of the

device.

VOLTAGE DROP

The maximum voltage drop across a fuse is based on

the specifications listed in the standards. It is

dependant upon the construction of the fuse and is

measured at 100% of rated current. A fuse element is

generally a thin wire or etched metal film exhibiting

some resistance to current flow. Because of this

resistance, a small voltage drop occurs across the

fuse terminals. In most cases, this voltage drop can

be ignored, as it is insignificant when compared to the

operating voltage of the circuit. However, attention

must be paid to the internal voltage drop of fuses with

low current ratings (50mA, 63mA, etc.) especially in

electrical circuits with low operating voltage drops due

to the extremely small cross sectional areas of their

melting elements. Voltage drops at 100% of rated

current are listed for most fuse types.

CURRENT RATING

The current rating of a fuse identifies its

current-carrying capacity based on a controlled set of

test conditions. When subjected to a current flow in

excess of its rated current for a predictable amount of

time, a fuse should reliably create an open circuit

condition. In order to avoid nuisance blowing and to

adequately protect the circuit, the rated current of a

fuse must be equal to or greater than the full load

operating current of the circuit and lower than the

lowest overload current.

The nominal operating current of a device is the

magnitude of current drawn (in RMS Amperes) after it

has been energized, warmed up, and is operating

normally. To determine the full load continuous

operating current of a circuit, the possible occurrence

of supply voltage fluctuations must be considered. In

cases of turn-on inrush currents or periodically

repeating pulses, please refer to the section on

melting integrals to derive the required fuse current

rating.

If a fuse manufactured according to the UL Standard

is replaced by a similarly rated fuse manufactured

according to the IEC 60127 Standard, safe blowing of

the fuse is no longer guaranteed. This is due to the

difference in each standard’s definition of rated

current. When loaded with its rated current, a UL fuse

is intended to eventually blow, whereas an IEC fuse is

designed to operate continuously under similar

conditions. Knowledge of how these definitions differ

is vital to selection of the proper fuse and its

appropriate current rating.

Ambient operating temperature and fuse contact

resistance must also be considered when determining

the fuse rating.

TEMPERATURE

Ambient temperature refers to the air temperature

immediately surrounding the fuse (1 cm) and is not to

be confused with room temperature. The fuse ambient

temperature is higher in many cases, because it is

enclosed or mounted near other heat-producing

components such as resistors, transformers, etc. To

prevent premature blowing of the fuse, ambient

temperatures should not exceed 70℃.

Contact resistance between the fuse and its

connections to a circuit can cause additional heat

buildup in the vicinity of the fuse terminals. Fuse clips,

fuseholders, hookup wire and solder track dimensions

must be sized adequately to minimize the effect of

contact resistance. Please refer to Table 4 for details.

Derating of the Fuse Rated Current Figure2

Higher ambient temperatures mean additional loading

on a fuse element. Since technical data is presented

based on a standard 23℃ ambient temperature,

either forced air cooling or de-rating of a fuse may be

necessary to ensure reliable operation in a higher

ambient environment. Derating is the process of

selecting a fuse with a higher rated current to allow for

its operation in an ambient environment above 23℃.

See Figure 2 above for typical derating criteria. For

example, a 1 Amp time-lag fuse shall be derated to

780mA when operating at 70℃ ambient conditions.

This is calculated by multiplying 1.0A times 0.78

(100%-22%) from the y-axis.

RESISTANCE

The resistance of a fuse is the measured voltage drop

divided by the applied test current. It is usually an

insignificant part of the total circuit resistance,

however, when using low amperage fuses in low

voltage circuits, the fuse resistance should be taken

into account.

It is common to refer to both the cold resistance and

hot resistance of a fuse. The actual operating point of

a fuse is typically somewhere in between these cold

and hot resistance points.

Cold resistance is measured using a currents of no

more than 10% of the fuse’s nominal rated current.

Cold resistance remains nearly constant at and below

10% of rated current. For this reason, this parameter

is an excellent predictor of a fuse quality level when

measured on a production line. Hot resistance is

calculated using the stabilized voltage drop across the

fuse at 100% of nominal rated current. Cold

resistance data on individual fuse types is available

upon request.

TIME VS. CURRENT CURVES

The lowest suitable fuse rated current is obtained by

rounding up the calculated value to the standardized

or typical current rating values shown on the fuse data

pages. The time vs. current characteristic curves

shown with each fuse series are a graphical

representation of the “pre-arcing” (fusing) time as a

function of fault current. Pre-arcing time is defined as

that period of time from the moment a current

sufficient to rupture the fuse element begins to flow

until arcing occurs. Pre-arcing time includes the actual

melting time of the fuse, as well as the heating-up

period.

The time vs. current characteristic curve

demonstrates the relationship between pre-arcing

time and fault current magnitude. Pre-arcing time is

expressed in seconds on the vertical (y) axis. The

ratio, IFault / IRated (fault current magnitude divided by

the rated current of the fuse), is expressed as a pure

number (no units) on the horizontal (x) axis. The

blowing curves are shown as an envelope for all listed

rated currents. The region between the two curves

identifies the range of blowing times for all ratings of a

particular fuse series. For standardized fuses, these

curves are defined by their respective fuse standard.

Individual curves exist for each rated current and may

be obtained upon request.

These curves enable the most precise selection of

fuse type and current rating for any application. They

should be used to verify that the fuse performance will

match all known circuit start-up and operating

conditions.

BREAKING CAPACITY

The breaking capacity of a fuse is a measure of the

maximum fault current which the fuse will safely

interrupt without exploding, rupturing, or causing a fire.

During a fault or short circuit condition, a fuse may

receive an instantaneous overload current many times

greater than its rated current. The fuse immediately

senses this increase in current flow and the element

begins to overheat and melt. The fuse must safely

interrupt this current flow and subsequently prevent

any potential arc restrike before a catastrophic fault or

short circuit conditions causes physical damage to the

downstream equipment.

The breaking capacity of a fuse is dependent on a

number of factors including fuse construction, circuit

operating voltage, current type (AC or DC) and circuit

power factor. The use of sand or ceramic disks in

miniature and subminiature fuse construction can

increase the maximum breaking capacity. These

materials tend to distribute the heat generated from a

fault condition over the entire fuse element. The

breaking capacity of a fuse is much lower in DC

applications than in AC applications. In an AC circuit,

the quenching of the arc is assisted by the periodic

passage of both voltage and current sine waves

through zero. This allows momentary clearing (cooling)

to occur within the confines of the fuse casing. As this

waveform effect is not present in DC circuits.

Interruption of similar fault currents can prove more

difficult. Greater reliance is made on the special

design features incorporated into the fuse casing for

arc-quenching purposes. In AC circuits, the power

factor (cos φ) can also have a considerable influence

on arc quenching behavior. If the circuit power factor

is reduced below the rated voltage of the fuse, the

breaking capacity of the fuse increases nonlinearly.

In all cases, the breaking capacity for fuses listed

herein are tested at a specific voltage level, current

level, and power factor.

MELTING INTEGRAL

The thermal energy required to melt a specific fuse

element is termed the melting integral and is

represented as a product of I2t (Amps2 x sec.). This

value is a parameter of the fuse itself and is

determined by the construction materials used.

Laboratory tests are conducted on individual fuse

ratings to determine a nominal melting I2t. During

these tests, a fault current (typically 10 times the rated

current of the fuse) is applied long enough to melt the

element. Studies have shown that the melting integral

of the fuse element remains constant when; (1) there

is no heat dissipation from the surface of the element

to the surrounding materials, and (2) no heat within

the fuse casing is conducted away by the fuse

contacts or terminals. Adiabatic heating occurs when

all of the heat energy causes the element to

completely melt. Upon test completion, the fuse

melting integral is easily calculated by squaring the

applied fault current and multiplying by the actual

melting time. This value is independent of

temperature and voltage fluctuations.

For fast-acting fuses, this Guide lists maximum

melting integrals. Fast-acting fuses are used to

protect devices from short duration, high amplitude

fault conditions. Turn-on transients or pulsed currents

are usually not present. For this reason, the circuit

designer requires a particular fuse rating to open prior

to a catastrophic fault. An example would be the

protection of semiconductor components which are

sensitive to any overcurrent condition. Selecting a

fuse rating with a maximum I2t value less than the

semiconductor’s own I2t rating guarantees that the

fuse will open before the semiconductor component is

damaged.

Time lag fuses are listed with their minimum melting

integral values. For capacitive or inductive circuits,

where normally anticipated turn-on transients, inrush

currents, surge or pulse currents are present, a

time-lag fuse is required. Selecting a fuse rating with a

minimum I2t value sufficiently greater than the

calculated I2t limit of the transient or pulse waveform

guarantees that the fuse will not cause nuisance

interruptions due to transient or pulse conditions.

When a fuse is pulsed with periodic inrush or

repetitive transient currents sufficiently powerful to

warm the fuse element but not strong enough to

cause the fuse to blow, the thermal stress caused by

the cyclical expansions and contractions of the fuse

element can lead to mechanical fatigue and

premature failure. Selecting the appropriate current

rating involves choosing a fuse with an I2t value

greater than or equal to the I2t value of the pulse

multiplied by a Pulse Factor (Fp). The formula for this

relationship is as follows:

I2tFuse ≥ I2tPulse X Fp

From Figure 3, determine which waveform

approximates the circuit turn-on condition. Calculate

the waveform’s approximate melting integral (I2tPulse)

using the corresponding formula from Figure 3.

Accuracy of this calculation can be improved by

obtaining from 3 to 6 inrush current oscillograms and

using the maximum recorded peak inrush current in

the calculation. This peak inrush current will vary

according to the level of the supply voltage at the

instant the device is turned on.

Pulse Waveform

Current-Time Integral Waveforms Figure 3

Ideally, an inrush current oscillogram should be

recorded with circuit energization coinciding with the

peak of the supply voltage waveform. Multiply the

resulting I2tPulse by the Pulse Factor (Fp). To determine

Fp, estimate the amplitude of the inrush current and

quantity of transient pulses the fuse will be subjected

to over the lifetime of the device and the approximate

time interval between pulses. Refer to the Pulse

Factor Derating Curve in Figure 4 when selecting Fp

for either a fast acting or time lag fuse.

The product of I2tPulse and Fp determines the prorated

I2t value of the inrush current waveform over the life

expectancy of the device. Lastly, select a fuse rating

with a minimum melting integral (I2tFuse) that exceeds

this prorated value.

For more complex waveforms or rapidly repeating

pulses (< 100ms interval), contact OUR for design

assistance. We strongly recommend that the selected

fuse be tested under normal, fault, and simulated life

0

0

0

0

I

I

I

I

0.386I

t 5t

tp

tp

I2tp

(1/2)I2tp

(1/3)I2tp

(1/2)I2t

cycle conditions to ensure a proper selection.

FUSE TYPES

Fuses can be classified by their construction as

miniature, subminiature, or blade-type.

Miniature cartridge fuses are commonly available in

dimensions of 5x20mm and 6.3x32mm. Their main

advantage is the relative ease of replacement when

used in conjunction with open fuse blocks or enclosed

fuseholders.

Subminiature fuse include the MEF, MET, MSF,

picofuse, and SM Fuses for surface mounting. These

have very small dimensions and are ideal for compact

circuit board layouts. Axial or radial leaded fuses, as

well as newer surface mounted types, permit cost

effective installation methods via automatic placement.

The MEF and MSF fuse series are electrically

equivalent to miniature glass cartridge, but offer much

lower voltage drop values and a higher resistance to

impact and vibration.

Blade-type fuses are typically used in low voltage,

high current applications. The automotive industry has

standardized on three sizes – small, standard, and

large. Blade-type fuses have become popular in many

non-automotive applications due to their ease of

replacement and low cost.

Protectors are recommended for protection of

secondary circuits or low voltage IC’s. Similar to high

grade fusible resistors, protectors are not bound by

competing component standards, and thus are

applicable worldwide.

Further subdivision of the above referenced fuse

types can be made under the topics of Manufacturing

Standard, Time vs. Current characteristic and Fault

Current Interruption Capability; each of which has

already been discussed and is summarized below.

The North American component standard for

miniature and subminiature fuses is UL 248-14. The

component standard adopted in Europe is IEC 60127.

Because of the fundamental differences in how rated

current is defined, it is not always possible to

interchange fuses built to these different standards.

Fuses are also subdivided according to their relative

prearcing Time vs. Current characteristics. This

characteristic determines how fuses react to varying

fault current conditions. While the UL Standard

identifies fuses with either Normal Blow or Time Delay

characteristics, the IEC standard defines several

characteristic types and lists their symbols as follows:

Pulse Factor Derating Curve Figure 4

Symbol Characteristic IEC 60127 (Sheet No.)

FF Very Quick-acting -4

F Quick-acting -2 -3 -4

M Medium Time-lag

T Time-lag -2 -3 -4

TT Long Time-lag -4

The UL Normal Blow characteristic roughly

corresponds to the IEC Quick-acting characteristic.

Since fuses exhibiting these characteristics have low

melting integrals, they are typically used to protect

devices which do not normally generate inrush or

surge currents. The standard application for Normal

Blow or Quick-acting fuses is to protect devices where

overcurrents or short circuit currents must be quickly

interrupted.

The higher melting integral (I2t) values associated with

UL Time Delay and IEC Time-lag fuses make them

ideal for protection of applications exhibiting turn-on

inrush, transient, or repetitive pulse currents. Such

applications include capacitive loads (i.e. battery

charging circuits) or inductive loads (i.e. power supply

and motor load circuits).

Fuses are also classified according to their fault

current interruption capability, commonly referred to

as the “Breaking Capacity” rating. Please refer to

Table 3 for breaking capacity values associated with

UL and IEC standards.

MARKINGS

Both UL/CSA and IEC fuse standards state that fuse

casings shall be marked with:

Manufacturers Name or Trademark

Rated Current (A or mA)

Rated Voltage (Volts)

Symbol for Time-Current Characteristic

Additionally, IEC 60127-2 requires a symbol for rated

breaking capacity (“L” for Low, “E” for Enhanced, “H”

for High) on miniature cartridge fuses. With the

exception of current rating, “microfuses” built to

UL/CSA 248-14 may have the above information

printed on the smallest shipping package only. At the

option of the manufacturer, fuses may also display

approval marks, part numbers, and color coding.

Picofuses and surface mount fuses, because of their

size, only have the manufacturer’s logo and current

rating printed on the body. Examples of various

markings are shown below:

Fuse Markings Figure 5

FUSEHOLDERS

Fuseholders can be either an open type or totally

enclosed type. Depending on the type of fuseholder

selected for an application, consideration must be

given to ambient temperature, electrical conductor

cross-sectional area and the maximum power

dissipation (self-heating) of the fuse chosen for use in

conjunction with the fuseholder. Maximum power

dissipation values are especially critical when

selecting enclosed fuseholders, since excessive heat

built up inside the fuseholder may cause material

damage and will certainly result in premature fuse

failure. The maximum power dissipation capability (ie.

rated power acceptance) of a fuseholder is listed on

the individual data pages. These values are valid for

an ambient temperature of 23℃ . When ambient

temperatures above 23℃ are encountered, power

acceptance derating curves have to be considered.

Power Acceptance Derating Curve Figure 6

The derated power acceptance value of the

fuseholder shall be greater than the maximum power

dissipation of the chosen fuse to insure a proper

selection. Particular care must be taken in application

where miniature ceramic cartridge fuses are used,

especially operation of these series in the “overload”

region cannot be excluded. Ceramic fuses can

generate excessive heat when operated at

150%-200% of rated current for several minutes.

Power dissipation values may become higher than

those listed in the respective data pages. The

recommended minimum cross sectional area of the

conductor connected to any fuseholder is determined

based on the anticipated maximum load condition,

normal circuit operating current and the power

dissipation value of the intended fuse. Note that the

circuit operating current is not equal to the rated

current of the intended fuse.

Table 4 lists minimum cross-sectional areas for

conducting paths (solder tracks) to PC board-mounted

fuseholders and conductor (wire) sizes required for

panel mount fuseholders.

Unlike fuses, individual fuseholders can be tested and

approved by both North American and European

safety agencies. However, the maximum permitted

fuseholder operating current varies according to each

agency’s individual approval. Operating currents in

accordance with UL/CSA approvals merely indicate

the maximum current-carrying capacity of the

fuseholder terminals. By comparison, operating

currents in accordance with European safety agency

approvals (SEMKO/VDE) include consideration of the

maximum power dissipation of the intended fuse at a

minimum conductor cross-section and maximum

ambient temperature. Thus, the approved operating

current limits in accordance with UL/CSA are

considerably higher than the approved limits in

accordance with SEMKO/VDE. In order to achieve the

highest degree of safety and to prevent possible

damage, it is recommended that fuse and holder

combinations be tested under actual load conditions.

Most circuit protection applications require that

enclosed fuseholders limit user contact with live parts

during operation or servicing. Fuseholders

manufactured with integral protection against electric

shock are termed “Shocksafe”. These holders are

designed such that live parts are not accessible when

the fuseholder is correctly assembled and installed on

panels or printed circuit boards. In addition, live parts

are not accessible during insertion or removal of the

fuse carrier. Compliance is checked by a “test finger”

as described in the standard IEC 60529. Shocksafe

fuseholders are commonly used in instrumentation,

medical and consumer products. All other

non-shocksafe fuseholders specified the in following

data pages fall under the PC1 category which

describes fuseholders without integral protection

against shock (ie. fuse blocks).

INSTALLATION

Miniature fuses may be installed in clips, open blocks,

enclosed fuseholders, or axial leads for direct

soldering. When bending wires on all axial leaded

fuses, a mechanical support is recommended. The

wires should be bent at a minimum of two (2) lead

diameters from the fuse body to prevent damage.

All subminiature fuses and protectors with wire leads

are suitable for wave and iron (hand) soldering

procedures. For wave soldering, we recommend a

soldering time of three (3) seconds at 260 ℃

maximum. For iron soldering, a duration of

approximately one (1) second at 350℃ is sufficient.

Heat sinking should be considered.

Surface mount fuses are constructed to handle all

typical SM soldering processes including wave, IR

reflow, and vapor phase. For inquiries about special

soldering methods, please contact us.

All protectors, subminiature and surface mount fuses

can be exposed to aqueous-based board wash

solutions. Since miniature cartridge fuses are not

sealed, provisions should be made if these types are

to be exposed to any board washing.

Maximum Load Values

Operating Current Fuse Power Dissipation

Minimum Cross Sections(Copper)

Conducting Path Conductor Size AWG

6.3A 1.6W 0.1mm2 0.75mm2 18-17

10.0A 2.5W 0.2mm2 1.50mm2 15-13

16.0A 4.0W 0.2mm2 2.50mm2 13-11

Conductor Requirements Table 4

Company: Fax to: OUR

Address: Applications Engineering

Fax: +86/ (0755)8286 5705(Shenzhen)

Fax: +86/ (0510)8561 5399(Wuxi)

Tel: Fax: +86/ (852)2541 9339(Hong Kong)

Fax:

E-mail:

1. Where do you intend to approve your device?

□ North America

□ Europe

□ Japan

□ Worldwide

□ No approvals required

2. How will the fuse or protector be mounted?

□ Replaceable, withholder or clips

□ Solderable, with leads

□ Solderable, surface mount

□ Specify

3. What is the maximum effective operating voltage?

V □ AC □ DC

4. What is the maximum continuous operating current?

A

5. What is the maximum ambient temperature in close proximity to the fuse or protector?

℃

6. What fault currents can occur?

What melting times do you require?

IFault1: A tMelt1,max: s

IFault2: A tMelt2,max: s

7. What is the maximum possible fault current?

IFault,max: A

8. Are there current pulses when turning on the device?

□ Yes, with the following waveform (Circle one)

You may also attach an oscillogram

□ No, there are no inrush current pulses

9. Insert the waveform melting integral, if known.

A2s

10. Quantity of pulses projected over the product life.

□

□ 1000

□ 10,000

□ 100,000

□ 1,000,000

11. Description of the device in which the fuse or protector will be installed (ie. primary circuit of TV set).

12. Estimated annual usage: pcs.

□ Please provide samples.

□ Please provide a quotation.

Company: Fax to: OUR

Address: Applications Engineering

Fax: +86/ (0755)8286 5705(Shenzhen)

Fax: +86/ (0510)8561 5399(Wuxi)

Tel: Fax: +86/ (852)2541 9339(Hong Kong)

Fax:

E-mail:

1. Where do you intend to approve your device?

□ North America

□ Europe

□ Japan

Worldwide

□ No approvals required

2. How will the fuse or protector be mounted?

Replaceable, withholder or clips

□ Solderable, with leads

□ Solderable, surface mount

□ Specify

3. What is the maximum effective operating voltage?

240 V AC □ DC

4. What is the maximum continuous operating current?

1.0 A

5. What is the maximum ambient temperature in close proximity to the fuse or protector?

40 ℃

6. What fault currents can occur?

What melting times do you require?

IFault1: 50 A tMelt1,max: 0.01 s

IFault2: A tMelt2,max: s

7. What is the maximum possible fault current?

IFault,max: 150 A

8. Are there current pulses when turning on the device?

Yes, with the following waveform (Circle one)

You may also attach an oscillogram

□ No, there are no inrush current pulses

9. Insert the waveform melting integral, if known.

？ A2s

10. Quantity of pulses projected over the product life.

□

□ 1000

□ 10,000

100,000

□ 1,000,000

11. Description of the device in which the fuse or protector will be installed (ie. primary circuit of TV set).

Primary circuit of switching power supply

12. Estimated annual usage: 50K pcs.

Please provide 10 samples.

Please provide a quotation.

Background

Transient overvoltages occurring in telephone lines

can usually be traced to two sources: (1) atmospheric

interference such as lightning, and (2) AC power lines.

Solid state circuitry in telephone subscriber equipment

and central office equipment is extremely sensitive to

these overvoltages and excessive currents. Various

types of current and voltage sensitive components

can be selected to protect telecommunications

equipment from lightning-induced and power

system-induced overvoltages. Listed herein is

background information and circuit design

considerations.

Equipment

Analog Telephones

ISDN Telephones

Modems

Facsimile Machines

Answering Machines

Switching Line Cards

Router Adapter Cards

Videoconferencing Equipment

xDSL Equipment

Line Test Equipment

PBX Equipment

Lightning

Nearby lightning strikes are the most common source

of atmospheric interference on telephone lines. Most

telephone lines are jacketed in shielded cables.

Nearby lightning can cause excessive currents to flow

on the shield surface, thereby inducing transient

overvoltages between the internal conductor and

shield itself. The levels of these overvoltages depend

on the construction of the cable and it’s internal

impedance. Indirect lightning can enter buried

telephone lines via ground currents. These currents

will exit the shield at each grounded pole along it’s

path until fully dissipated. Since the cable has a fixed

impedance, a potential gradient will be created along

the cable’s entire length. The gradient will induce a

potential difference between the cable and soil. At

several points along the cable, it’s dielectric value will

be exceeded, causing a puncture. At each puncture

point, a portion of the lightning currents will eventually

enter sensitive telecommunication equipment.

Lightning Interference Figure7

Power System

The power source for telecommunications equipment

is taken from commercial AC power lines. Typically,

telephone and power lines are run side-by-side

suspended on poles or buried in the earth.

A telephone line consists of many pairs of conductors

arranged in twisted pairs called tip and ring lines.

Regardless of location, twisted pairs are capable of

picking up transient overvoltages and transmitting

them to central office or subscriber equipment. Two

sources of power system interference can be

attributed to power induction and power cross. Power

induction is the result of circulating currents in the

earth or high currents in adjacent lines induced on

telephone lines due to their close proximity to power

lines. The more damaging source of transient

overvoltages is from direct physical contact (ie.

short-circuit) between telephone and power lines.

Power cross can last several minutes and cause

excessive voltage development and current flow into

telephone equipment. Power cross has been traced

as the cause of many building and equipment fires.

Power System Interference Figure 8

Effects

During recent years, increased usage of telephone

lines for voice, data, and video transmission has

caused an increased sensitivity to overvoltages. Solid

state IC’s are much more susceptible to damage or

failure from transients and line noise conditions. Since

these surges are typically unidirectional impulses,

they can cause permanent damage to components,

equipment fires and shock hazards. Temporary faults,

such as tip and ring imbalance, are also common

occurrences. The predominant industry standards are

below.

UL 1950 – 3rd Edition

When introduced in April 2000, one objective of UL

1950, “Safety of Information Technology Equipment,”

was to protect users from fire hazard and electrical

shock. Functionality of the equipment was not

covered under this standard. Test procedures in

Section 6.6 required that the telecommunication

equipment be wrapped in cheesecloth and connected

to a power source through a 2 Amp time delay fuse or

No. 32 AWG wire. A series of overvoltages and

overcurrents simulating long and short term power

induction and power cross conditions are applied

across the equipment’s tip and ring line input. The

purpose of the 2 Amp test fuse or No. 32AWG wire is

to simulate building wiring. Equipment is to be tested

in both line-to-ground and line-to-line modes as

shown:

Test Voltage(VRMS) Current(A) Duration

L1/M1 600 40 1.5sec

L2/M2 600 7 5sec.

L3/M3 600 2.2 30min.

UL 1950 Test conditions Table5

The varying currents simulate short and long term

induction and power cross. In all tests, the purpose of

the equipment’s overcurrent protector (fuse) is to

safely interrupt the fault current without ignition or

charring of the cheesecloth and before the wiring

simulator opens. The equipment fuse must limit

current to within the acceptable range as shown in

Figure 9. The fuse’s melting integral (I2t) must be less

than that of the wiring simulator at all test points to

guarantee a successful circuit interruption.

Additionally, tests L4/M4 prescribe criteria where the

equipment fuse is jumped red and 600 Volts is applied

at 135% of the fuse current rating (2.2 Amps max) for

up to 30 minutes. Power dissipation (selfheanting) is

monitored in nearby circuit components.

UL 1950 Wiring Simulator Characteristics Figure9

All telecommunication lines entering a building pass

through a primary protector shunting voltages in

excess of 600 Volts. Unfortunately, these coarse

protectors allow potentially damaging voltages to

remain on the lines. The purpose of the secondary

equipment overvoltage device is to clamp

overvoltages during power cross conditions and

protect the downstream load. When solid state

overvoltage devices fail, it is usually in the shorted

mode, producing a limited impedance path of current

flow. Depending on the impedance value, this can

potentially cause a fire hazard in the building wiring or

the equipment. The equipment fuse is used to

eliminate these hazardous conditions. The designer

should exercise caution during fuse selection, since

too low of a current rating may pass UL 1950

satisfactorily, but not withstand the simulated lightning

surge waveforms describe in the next sections. Too

high of a fuse rating can potentially allow damaging

currents to destroy downstream components. At

present, UL 1950 – 3rd Edition must be referenced to

test all new Information Technology equipment. In

2005, all new equipment must be Listed to UL 60950

– 3rd Edition.

FCC Part 68

Most products or devices which interface to the U.S.

or Canadian telecommunications network must be

registered with the Federal Communications

Commissions under Part 68. “Connection of Terminal

Equipment to the Telephone Network” is a

governmental regulation which prescribes a series of

tests and procedures that are designed to determine if

equipment has any potential to harm the network.

This standard does not address subscriber equipment

requirements – only harm to network criteria.

Specifically, Section 302 lists a series of simulated

lightning waveforms that potentially can cause fire and

shock hazards to humans and equipment. The basic

tests are as follows:

Surge Type Voltage

(V)

Current

(A) Waveform

#

Pulses

Metallic 800 100 10x560μs 2

Longitudinal 1500 200 10x160μs 2

Longitudinal 2500 1000 2x10μs 6

FCC Test Conditions Table 6

Metallic surges are applied tip to ring while

longitudinal surges are applied between tip to ground

and ring to ground. The primary objective of these

tests is to allow for telecommunications equipment

interface circuitry to safely divert lightning-like

transients to ground. If the circuitry maintains the path

to ground after the transient subsides, the potential for

network interference exists due to line imbalance. The

equipment should remain fully operational after these

surge voltages are applied. This means that the

equipment fuse does not open and the overvoltage

device returns to it’s high impedance state.

FCC Metallic Surge Waveform Figure 10

Bellcore 1089

Many manufacturers are now required to not only

pass UL 1950 and FCC Part 68, but also comply with

Bellcore GR-1089-CORE: “Electromagnetic

Compatibility and Electrical Safety – Generic Criteria

for Network Telecommunications Equipment.” Already

a leading provider of communications software and

consulting services based on extensive research,

Telcordia Technologies (formerly bellcore) creates the

business solutions that make information technology

work for telecommunications carriers, businesses and

governments worldwide. It is quite common for

equipment supplied to the Bell operating company

clients to be subjected to GR-1089-CORE. This

standard essentially combines lighting immunity, AC

power cross, and power induction criteria into one

document. Because of it’s higher energy surge

waveforms documents. Because of it’s higher energy

surge waveforms and higher pulse repetition, the

designer must select more surge tolerant circuitry

than required by UL and FCC alone. Unlike UL

1950-3rd Edition, Bellcore does not impose a limit on

the fuse rating.

These simulated lightning and AC power fault tests

are applied to the telecommunications (tip & ring)

ports of the equipment and assume it is externally

protected by 3-milcarbon blocks. First – level lightning

surge criteria, shown in Table 7, states that the

equipment shall be undamaged and continue to

operate properly after the waveform is removed.

Second-level lightning surge criteria, shown in Table 8,

allows the equipment to sustain damage, but shall not

present a fire, fragmentation, or electrical safety

hazard.

Surge No. Voltage

(v)

Current

(A) Waveform #Pulses

1 600 100 10x1000μs 25

2 1000 100 10x360μs 25

3 1000 100 10x1000μs 25

4 2500 500 2x10μs 10

5 1000 25 10x360μs 5

Bellcore 1st Level Lightning Table 7

Surge No. Voltage(V) Current(A) Waveform #Pulses

1 5000 500 2x10μs 1

Bellcore 2nd Level Lightning Table 8

Note that in Table 7, Surge No. 3 may be performed in

lieu of Surge Nos. 1 and 2 to expedite testing. The

equipment must withstand a total of 50 pulses (25 per

polarity) for Surge Nos.1 thru 3 and remain

operational. Various longitudinal test connections of

the tip and ring ports to the surge generator and

ground are specified in the standard.

Bellcore Surge No.3 Waveform Figure11

First-level AP Power Fault criteria, shown in Table 9,

states that the equipment shall be undamaged and

continue to operate properly after the waveform is

removed. Second-level AC Power Fault criteria,

shown in Table 10, allows the equipment to sustain

damage, but shall not present a fire, fragmentation, or

electrical safety hazard.

Test

No.

Voltage

(VRMS) Current(A) Duration

＃

Pulses

1 50 0.33 15 min. 1

2 100 0.17 15 min. 1

3 200,400,600 1 1 sec. 60

4 1000 1 1 sec. 60

5 600 See Std. 5 sec. 60

Bellcore 1st Level AC Power Fault Table9

Test No. Voltage(VRMS) Current(A) Duration

1 120,277 25 15 min.

2 600 60 5 sec.

3 600 7 5 sec.

4 100-600 2.2 15 min.

5 600 See Std. 15 min.

Bellcor 2nd Level AC Power Fault Table10

In Table 10, tests Nos. 1 and 2 simulate secondary

and primary power cross conditions, respectively. The

remaining tests prescribe criteria for short and long

term power induction. The designer, at their discretion,

may elect to substitute prior UL 1950 test results for

this section. Only Test No. 1, conducted at 277 Volts,

must be performed, since it is not addressed in UL

1950.

Table 10 requirements are intended to cover

non-customer premises equipment (non-CPE).

Criteria for terminal equipment (telephone sets, PBX,

etc.) located on the customer premises is subjected to

two AC power cross conditions. First, 300VAC is

applied between exposed conductive surfaces and

ground and then 600 VAC is applied in both metallic

and longitudinal modes across the tip & ring ports and

ground. These test voltages are initially applied at 30

VAC and raised slowly such that current is limited to

100mA and the voltage does not rise greater than 20

percent over any 15 minute interval. Voltage is

increased until one of the following conditions occurs:

(1) the maximum voltage is reached, (2)the current

reaches 20 Amps or the wiring simulator (1.6A glass

fuse) opens or, (3) the equipment fails open-circuited.

If the wiring simulator opens or the equipment fails,

the equipment has failed the power cross test.

ITU-T Recommendation K.20

The International Telecommunications Union (ITU) is

an intergovernmental organization, consisting of 185

member states within which the public and private

sectors cooperate for the development of

telecommunications. The ITU adopts international

regulations and treaties governing all terrestrial and

space uses of the frequency spectrum, within which

countries adopt their own national legislation. ITU also

develops standards to facilitate the interconnection of

telecommunication systems worldwide regardless of

the type of technology used. Recommendation K.20

named, “Resistibility of Telecommunications Switching

Equipment to Overvoltages and Overcurrents” was

issued in October of 1996. This standard relates to

PBX exchanges and similar switching centers and is

concerned mainly with stress conditions to be applied

to points of connections to subscriber lines. Tests

include surges due to lightning on or near telephone

central offices, short term induction of voltages from

adjacent power lines or railways, and direct contact

between telephone lines, power lines and electrostatic

discharges. A summary of tests in Table 11 follows:

Test No.Voltage

(V)

Current

(A) Duration #Pulses

1a 1000 67 10x700μs 30

1b 4000 See Std. 10x700μs 30

2a 600 1 0.2 sec. 5

2b 600 1 1 sec. 5

3 230 60,3,1 15 min. 1/5

ITU – T K.20 Test Conditions Table 11

Tests 1a and 1b describe metallic and longitudinal

lightning surges conducted at 1000 volts and 4000

Volts peak. Test 1b only applies to equipment exposed

to harsh environments where a specific type of

overvoltage device is agreed upon. The time interval

between consecutive surges is one minute and the

polarity is reversed between each surge.

In Tests 2a and 2b, power induction is simulated with

five surges applied at 600Volts thru a 600Ω resistor

for 0.2 seconds and one second, respectively. In the

aforementioned tests, the equipment shall withstand

the surges without damage and shall continue to

operate within the specified limits afterwards. A power

cross voltage of 230 Volts in Test 3 is applied for 15

minutes each through varying resistor values. These

values are to simulate power cross incidents at

varying distances from the telephone exchange. The

power cross tests may damage the equipment

irreparably, but the fuse shall safely interrupt the fault

and no fire may occur.

Telecom Circuit Protector

While many types of OUR time-lag or time-delay fuses

may be considered for telecom line protection, we

recommend the surface mountable Telecom Circuit

Protector (TCP). The TCP has been tested under the

telecommunications standards described herein.

Product features include:

* Low Profile Chip

* Small Footprint

* Non-flammable Housing

* Auto-Insertable

* Surge Tolerant

* Low Voltage Drop

* Zero Leakage Current

Protector Selection

Circuit analysis must be examined to determine the

proper TCP and resistor ratings to successfully pass

FCC lightning waveforms. Two typical tip & ring

interface circuits are shown below:

Fused Tip Line Interface Figure 12

Fused Tip & Ring Line Interface Figure 13

In these sample interface circuits, the series resistor(s)

are employed to limit the peak currents seen during

the various lightning immunity tests. The TCP is

required to safely interrupt current flow to the

equipment during a sustained power cross condition.

The overvoltage device, placed in parallel, should limit

and divert transient overvoltages seen during a power

cross or power induction condition. Upon sensing a

transient, the overvoltaged device will switch to a low

“on state” voltage. Current conduction will continue

through the over-voltage device until the fuse

interrupts the circuit or the fault is removed.

In order for the OUR TCP-1A to pass FCC Part 68

metallic surges operationally, the following series

resistor example calculations from Figure 13 can be

made.

FCC Part 68 Lightning Surges (10X560μs)

1) Total Loop Impedance:

RTotal = RSource + RTip +RRing

(where RTip = RRing):

RTotal = RSource + 2RTip

2) Generator Source Impedance:

RSource = I(Source)

V(Source)

RSource = 100A

800V = 8Ω

3) Fuse Peak Surge Current:

IPeak (10x560μs) = Value from Data sheet

IPeak (10x560μs) = 40 Amps

4) Series Resistor Value (s):

RTotal = (10x560us)I(Peak

V(Source)

RTotal = 40A

800V = 20Ω

RTip = RRing = 2

R(Source))-(R(Total)

RTip = RRing = 2

8ohm)-(20ohm = 6Ω

For circuits corresponding to Figure 12 where only the

tip line is fused, the resistor value should be doubled

to 12Ω or greater. Since internal impedances can

vary in different applications, the designer is urged to

perform these transient overvoltage tests on the

equipment prior to submission for agency approval.

Please note that the TCP-1.5 A with a FCC Part 68

surge current rating of 108 Amps will not require any

additional series resistance.

Recall that the resistor’s purpose is to limit peak

currents prescribed in the lightning simulation tests.

Please note that surge current capability of the

overvoltage device must also be checked if series

resistors are eliminated from the circuit. Overvoltage

device manufacturers typically provide surge

waveform test data on their components as required

by FCC, ITU, and Bellcore. Contact OUR for other

circuit design examples when compliance with

Bellcore or ITU standards is required.

For power supply or battery charger applications in

telecommunications equipment, please refer to the

following fuse types: 5x20mm, MEF, MAT, MST, Chip

Fuses, and Blade-type fuses.

Standards Agencies

Underwriters Laboratories, Inc.

333 Pfingsten Road

Northbrook, IL 60062

USA

TEL: +1/ (708) 272-8800

FAX: +1/ (708) 272-8129

WEB: www.ul.com

Federal Communication Commission

1919 M Street NW

Washington, DC 20554

USA

TEL: +1/ (202) 418-0200

FAX: +1/ (202) 418-2825

WEB: www.fcc.gov

Telcordia Technologies (Bellcore)

8 Corporate Place

Piscataway, NJ 08854

USA

TEL: +1/ (732) 699-5800

FAX: +1/ (732) 336-2559

WEB: www.telcordia.com

International Telecommunications Union

Place des Nations

CH-1211 Geneva 20

Switzerland

TEL: +41/ 22 730 5111

WEB: www.itu.ch