facilities electricalequipmentsafety

8/12/2019 Facilities Electricalequipmentsafety

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E A LTH AND SAFETYh

CONTENTS PAGE

1. Introduction 4

2. Electrical Hazards 4

3. Electrical Accidents and First Aid 5

4. General Safety Requirements 5

5. Detailed Safety Requirements 8

6. Testing Electrical Equipment 11

7. Testing Residual Circuit Devices 11

8. Experimental Equipment 11

9. Miscellaneous Equipment 15

10.High-Risk Areas and Activities 16

11.References 18

ELECTRICAL EQUIPMENT SAFETY GUIDE

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1. INTRODUCTION

2. ELECTRICAL HAZARDS

2.1 Shock

2.2 Burns

2.3 Fire and Explosion

3. ELECTRICAL ACCIDENTS AND FIRST-AID

4. GENERAL SAFETY REQUIREMENTS

4.1 Using Electrical Equipment

4.2 Live Work

4.3 Classes of Electrical Equipment

Class 0

Class I

Class IIAClass IIB

Class III

4.4 Types of Equipment

Portable Equipment

Fixed Equipment

Stationary Equipment

4.5 Personal Equipment

5. DETAILED SAFETY REQUIREMENTS

5.1 Supply Sockets

5.2 Plugs

5.3 Plug Fuses

5.4 Connecting Plugs to Cables

5.5 Flexible Cables

5.6 Joining Cables

5.7 Extension Cables

5.8 Connection of Cables to Equipment

5.9 Equipment Insulation

5.10Ventilation and Cooling

5.11Equipment Fuses

5.12Disconnection

6. TESTING ELECTRICAL EQUIPMENT

7. TESTING RESIDUAL CURRENT DEVICES (RCDS)SG11

8. EXPERIMENTAL EQUIPMENT

8.2 General Points

Short Cuts

Operational at Low Safe Voltages

Colour Codes

Design to BS Specifications

Live Work

Isolation

Clear Work Area

Equipment Left Operating Unattended ina Dangerous Condition

Mat switches

Mains Power Supplies to Electronic

Equipment

8.3 Trials of Proto-types

8.4 Isolation Switches

8.5 Earth Bonding

8.6 Protection of Cables against Mechanical

Damage

8.7 Internal Fuses

8.8 Insulation

8.9 Exposed Terminals

8.10Interlocks

8.11 Non-standard Supply Voltages, Plugs and

Sockets

8.12Transformers

Isolation Transformers

Variacs

8.13Capacitors

8.14Batteries and AccumulatorsLithium Cells

8.15 Water Flow Systems

8.16Furnaces

8.17Explosion Protection in Highly Flammable

Atmospheres

8.18High Voltage Work

8.19Fieldwork

8.20Buzz Plugs

8.21Electrostatic Hazards

8.22Thermal Cut-outs

9. MISCELLANEOUS EQUIPMENT

9.1 Light Bulbs

9.2 Audio-Visual Equipment

9.3 Electrophoresis

9.4 Power Washers

9.5 Construction Site Equipment

9.6 Foreign Equipment

9.7 Overseas Power Supplies

10.HIGH RISK AREAS AND ACTIVITIES

10.1General Points

10.2Electrical and/or Electronic Workshops

10.3Electrical Engineering Laboratories

ProvisionsProcedures

10.4Aquaria

10.5Power Washed Animal Houses

10.6Construction Sites and Buildings

Maintenance Work

10.7Portable Generators

11.REFERENCES

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DETAILED CONTENTS


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1. INTRODUCTION

Electrical accidents are not the most common type of

occupational accident. H ow ever, the proportion of

electrical accidents that cause loss of life is very high

compared to the proportion of fata lities resulting from

other types of occupationa l accident, and electrical faults

are the second main cause of industrial fires in the United

Kingdom. The majority of electrical accidents involve

equipment that is defective due to internal insulation

failure, inadequate earthing, inappropriate fusing or

incorrect wiring. These defects pose a threa t to personal

safety by causing electric shocks, burns, explosions and

fires.

In order to safeguard U niversity staff, students and

property aga inst these potential ha zards, th is guide hasbeen prepared to a dvise departmental and area

mana gements on the procedures and precautions tha t

should be employed to maintain electrical equipment in a

safe condition. Sources of supply of the items mentioned

are listed in and the practical aspects of testing electrical

equipment are described in the Safety G uide.

2. ELECTRICAL HAZARDS

Electricity does not alert the human senses; it cannot be

seen, heard or smelt. The potential hazards posed by

electricity a nd defective electrical equipment a re electric

shock, burns, fi re, explosion, injury from involuntar y

reaction to otherwise harmless shocks, such as falls, and

radiation damage from radiation in the microwave and

ultra violet ranges.

2.1Shock

Electric shock affects the nervous system and can cause

muscular contraction including the inability to let-go thus

increasing the period o f conta ct and possibility of fat ality.

If the current passes through the heart it upsets its

pumping action and can cause death. In addition, a shock

that in itself might not be serious may cause a reaction

resulting in loss of ba lance and a subsequent fall w hich

could have serious consequences.

Shock is usually caused by one pa rt of the body touching

a live conductor whilst another part is in contact with

earth thus permitting the passage of current through the

body. Shock can be felt from voltages as low as 15v and

at 2025v most people experience pain. At higher

voltages the victim may not be a ble to let go o f the

conductor and suffer burns. D eath can be caused, in

appropriate conditions, by voltages as low as 70v, but

generally speaking the danger of death is small, but notentirely negligible, at voltages below 120v ac.

Nevertheless, voltages in excess of 50v ac or 120v dc are

regarded a s dangerous.

Mo st serious and f ata l accidents involve the normal

domestic and industrial volta ge of 240v acand involve

currents of 25-30ma and over. Direct current (dc) does

not a ffect the body of the same degree as alternating

current (ac) as shown below.

Response ac dc

Threshold of feeling 1ma 5ma

M uscular paralysis (spasm) 15ma 40ma

Ventricular fi brillation 70ma 140ma

It is important to realise that it is the current passing

through the bo dy tha t kills. The current is dictat ed by tw o

main f actors. Firstly, t he voltage or driving force behind

the current, as explained earlier, and secondly, theresistance of the body between the live conductor and

return (normally earth) forming the circuit. This

resistance varies depending on the points of contact and

the skin moisture condition. Between the ears for

example, the internal resistance is only 100 ohms, whilst

from hand to foot it is 500 ohms. The skin resistance

varies from 1 kohms for w et skin to o ver 50 kohms for

dry skin. The important f act t o not e from these fi gures is

that w ith the exception of t he dry skin condition, w hich is

comparat ively rare given the normal degree of human

perspiration, all these conditions at the mains voltage of

240v permit currents equal to or in excess of 25ma to

flow that could prove fatal or arrest respiration.

The time of current passage through the body also

influences the degree of damage. Although the

current/time levels vary w ith fi tness, etc, the follow ing

conditions would no rmally cause ventricular fib rillation in

the average person of 70kg body w eight

50 ma for 4.5s

100 ma for 1.3s

250 ma fo r 200ms

500 ma for 50 ms

1a fo r 10 ms.

These values are obtained from the relationship

I = 116/T1/2 w here I = current in millia mps (ma) a nd

T = time in second s (s).

Further information on these effects is given in Reference 1.

This information explains why Residual Current Devices

(RCD s) are effective in avoiding the ha rmful

consequences of electrical a ccidents see lat er Sections.

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2.2Burns

Burns can be caused by the passage of heavy currents

through the body if it is in contact with a conductor and

earth, or by direct contact w ith an electrically heated

surface, or by the intense heat generated by arcs produced

from a short circuit. Although the area of an electrical

burn may be relatively small the depth is likely to be

greater than it appears, with damage to the underlying

tissue.

2.3Fire and Explosion

Fire (and explosion) can be caused by sparks or arcs

igniting flammable material or highly flammable

atmospheres, or short circuits producing high currents

w ith a high associated heating effect, or current

overload ing causing heating and dama ge to insulation, orthe insulation of old w iring that ha s been in use for ma ny

years becoming brittle and losing its insulating properties

leading t o a short circuit.

3. ELECTRICAL ACCIDENTS AND FIRST-AID

Instruction on the first-aid techniques described below is

given in fi rst-aid t raining courses that are orga nised b y

Safety Services. Further practical details are given in

Reference 2. Obviously it is prudent to be familiar w ith

these procedures before they may be needed; a poster

summarising the technique outlined in (Reference 2) is

available from Safety Services and must be posted in

Electrical and Electronic Workshops, Electrical

Engineering La bora tories and similar a reas.

If an electrical accident shock, burns or fire should

occur the following procedure should be ad opted

1. The first thing to do is to isolate the electrical supply

providing it is safe to do so. If necessary the entire

building should be isolated using the building mains

isolation switch. If someone is known or suspected to

be in contact w ith the mains supply, or a supply of

appreciable voltage, the victim must not be touched

directly with bare hands etc. The rescuer must use a

length of dry rope, wood, or a blanket to pry or pull

the victim loose and, if possible, stand on dry

insulating mat erial w hilst d oing so.

2. If following isolation from the mains, the shock has

caused the patient to stop breathing, artificial

ventilation must be started immediately. If the heart

has stopped beating (the signs of which are indicated

by t he casualtys colour remaining unchanged or

becoming blue/grey, w idely dilated pupils and ab sence

of pulse) external chest compression must be appliedas well as artificial ventilation. In these circumstances

a fi rst-aider wo rking alone should apply 15 heart

compressions followed by tw o deep lung infla tion

using mouth-to-mouth ventilation. An assistant must

be sent to call an ambulance as soon as possible.

3. Follow ing revival, place the casualty in the recovery

position, cover with a blanket to keep him/her wa rm,

and provide reassurance until an ambulance or

physician arrives. Meanwhile continue to observe the

casualty carefully in case a relapse occurs. In which

case re-applicat ion of art ificia l ventilation a nd/or chest

compression will be required. Arrange removal to

hospital in all cases where the casualty has required

resuscitation, w as unconscious, sustained b urns or

developed any of the symptoms and signs of shock.

4. If electrical burns have been sustained place the

burned part under slowly running cold water or

immerse in cold water for at least 10 minutes or untilthe pain ceases. Remove any items of a constrictive

nature such as rings, bangles etc, before parts begin to

swell. La y the casualty dow n and cover the injured

area w ith a clean non-fluffy dressing. Reassure the

casualty at all stages. Do not apply lotions or

ointments. D o no t prick blisters, b reathe or cough

over, or touch the burned area. If the burns are

serious, call an ambulance by dialling Ext 5555.

Report C entre staf f w ill call the ambulance, guide it to

building and send tra ined fi rst aiders to assist a s

required.

5. Fire procedures are described in Fire Action N otices.

Water and foam extinguishers must not be used on

electrically induced fi res; carbon diox ide or dry

powder extinguishers must be used.

4. GENERAL SAFETY REQUIREMENTS

Electrical equipment must not be used if there is any

doubt regarding its safety. Supervisors, D epartmental

Safety Officers, departmental workshop staff, maintenance

engineers or Safety Services should be contacted in case of

doubt.

Whenever possible equ ipment, electrical components a nd

cables conforming to a British Standard (Reference 3)

should be purchased and used; vacuum cleaners to BS

5415, safety isolating tran sformers to B S3535 and no rmal

flexible cables (cords or flexes) to BS 6500 for example.

When obtaining foreign equipment the purchaser should

ensure that the equipment is at least as safe as equipment

constructed to the equivalent British Standa rd.

A means of isolation must be readily accessible.

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4.1Using Electrical Equipment

In order to obtain satisfactory standards of electrical

safety when using single phase mains powered electrical

equipment the following conditions must be met.

Equipment conforming to BS 3456 should bepurcha sed w henever possible.

Manufacturers or suppliers instructions must be readand understood before an unfamiliar item of

equipment is used for the first time.

The mains supply socket (and temporary installations)must be correctly installed ie wired, adequately

earthed, appropriately fused a nd comply w ith the IEE

Regulations (References 4 and 5).

The mains supply plug and other components must beadequately rated and constructed for their application,

in good condition (no cracks or pieces missing),correctly w ired, a ppropriately fused and, w here

applicable, the supply cable sheath clamped inside

(Reference 6).

The cable from the plug to the equipment must be ofadequate duty to carry the required current,

unknotted, ad equately insulated, free from cracks,

frays a nd kinks, long enough to be used w ithout

stretching, and not present a trip hazard (Reference 6).

The cable must be correctly connected and anchoredinside the equipment, an insulating grommet fitted

around the point of entry through th e case (if

conductive), and the earth conductor connected t o the

case of equipment (if conductive) that is not all-

insulated (Class IIA) or double-insulated (Class IIB)

(Reference 6).

The cab le must be secured inside the equipment bynon-conducting fa ces so tha t it cannot slip.

The equipment must have sufficient insulation betweenall live parts and external surfaces to reduce leakage

currents to a safe level.

In areas of particular haza rd the need for measures asfollows must be considered

fla meproof or intrinsically safe equipment where

essential in explosive atmo spheres

operation at voltages as low as practical (25V ac

or 60v dc ripple free) where a particularly low

body resistance is anticipated

where appropriately extra low voltages cannot be

sensibly achieved, the application of high

sensitivity (normally 20 or 30 ma) Residual

Current D evices (RCD s), a nd w herever practical,

of the permanently fixed type

safeguards against mechanical damage and

extremes of temperature (it may be necessary to

consider actual maximum temperatures in selecting

a f orm of insulation eg a heat resistant fl exible

cable to BS 6141).

The equipment must be annually inspected, tested andlabelled (Section 6).

When internal a djustments, repairs or modifi cationsare necessary, the equipment must be isolated at the

mains supply socket, the plug removed from the socket

before work begins and insulated ha nd too ls should be

used.

4.2Live Work

No live working until a risk assessment has been

completed and the significant find ings recorded in writing

and brought to the attention of the relevant people. Work

on exposed live conductors at voltages of greater than 50v

ac or 120v dc (smoothed or ripple free) must only be

undertaken by persons w ith the technical know ledge to b e

aware of dangers when conductors are exposed, and thefollowing conditions met

Access to areas where such conductors are exposedshould be restricted to personnel who have been given

specific permission by the Head of D epartment o r his

nominee in charge of the area.

Working spaces should be kept clear so thatmovements are not restricted whilst work near live

conductors is in progress and due allowa nce should be

made w here groups of students witness

demonstrations under these circumstances.

Clearly labelled isolators should be provided for allsupplies to equipment where bare conductors may be

exposed when live at dangerous voltages.

When live conductors at dangerous voltages areexposed one person should never be present alone; at

least one other person should be present to isolate

supplies in an emergency and to summon aid.

If possible live work should be carried out in aResidual C urrent Circuit Breaker (RCD ) protected

area, o r a RC D socket extension cable connected

between the equipment and mains supply socket

(Reference 7). RC D plugs should be used w ith cautio n

as they are susceptible to damage.

A telephone must be easily available to summon anambulance at all times when such w ork is carried out.

Mo re information relating to live w ork on experimental

apparatus is given in Section 8.2.

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4.3Classes of Electrical Equipment

The various methods used by equipment manufacturers to

provide safety for users of electrical equipment may be

classified as follows (nb equipment that is directly

connected to a single or three-phase mains supply is not

included in this classification).

Cl ass O

Equipment in w hich exposed conductive parts ma y

present a shock hazard in the event of a fault o ccurring in

the basic safety insulation, ie the equipment has functional

insulation only a nd no provision is made for earthing any

external metal parts.

Class O equipment is dangerous and must not be used at

the University w ithout prior permission from the

University Electrical Engineer.

Class I

Equipment with a metal case that must be earthed and

must be connected to the mains supply plug using a three-

core cable.

Class I I A

Equipment that is all-insulated (plastic cased for example)

and must be connected to the mains supply plug using a

two-core cable.

Class I I B

Equipment t hat is double-insulated, ha s an unearthed

metal case and must be connected to the mains supply

plug using a two-core cable. This class of equipment is

usually labelled with the concentric squares symbol.

Class I I I

Equipment tha t is designed fo r operation a t volta ges of

less than 50v ac or dc.

4.4Types of Equipment

There are three main t ypes of electrical equipment

Portable Equipment

Which is either

intended to be hand-held during use, eg drills,soldering irons, inspection lamps, saws, vacuum

cleaners, floor polishers, domestic irons, etc;

or

not primarily intended fo r ha nd-held use but can betouched or moved w hilst in operation or easily moved

from one place to ano ther whilst connected to the

supply, eg desk lamps, electric fi res and heaters,

photogra phic lighting equipment, typewriters, port able

television receivers, kitchen equipment such a s mixers,

stirrers, etc, laboratory bench-top equipment such ashotplates, ovens, variacs, heaters etc.

Fixed Equipment

Which is fastened to a support or otherwise secured in a

specific location, eg workshop machinery such as lathes,

milling machines, etc a nd substant ial plant.

Stationary Equi pment

Which is either fixed or has a mass exceeding 18 kg and is

not provided with a carrying handle, eg office machines

such as duplicators, photo-copiers etc, large television

receivers, refrigerators, large ovens, large computers, etc.

4.5Personal Equipment

Personal equipment owned by students residing in halls of

residence such as kettles, calculators, tape recorders,

record players, etc must be maintained by their owners to

the same standards of electrical safety as those required

for the University equipment.

With the exception of residential accommodation all

electrical equipment connected to the University Electrical

supply system must be tested in accordance with the

University Cod e of Pra ctice Testing El ectrical E quipment.

Any equipment that d oes not conform to t hese

requirements must not be used on University premises or

during University activities.

If a member of hall or d epartment staff no tices students or

staff indulging in dangerous electrical practices such as

poor wiring, using exposed mains connections, etc the

danger must be pointed out to the student or member of

staff concerned and if n ecessary the H all Warden or H ead

of Department informed who must then take the

appropriate a ction to curta il the danger.

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5. DETAILED SAFETY REQUIREMENTS

This section explains in more depth the general guidance

given in Section 4 and Reference 8.

5.1Supply Sockets

Mains supply sockets or fixed supplies at voltages above

50v ac or 120v dc must be correctly wired, adequately

earthed, fused, a nd comply with the IEE Regulations for

the Electrical Equipment of Buildings (References 4 and

5).

The installation, maintenance and repair of mains supply

sockets and the associated ring-main fuses must not be

carried out by departmental sta ff. The installation of new

electrical supplies is carried out by the Estates Office, and

the repair and maintenance of existing supplies by theEstates Office Maintenance Department.

Equipment must not be plugged into light bulb sockets, or

circuits intended for lighting purposes, or circuits intended

for emergency use only. Approved multi-way sockets

connected by a short 13a rated flexible cable and standa r d

13a plug and socket may be used but care must be taken

not t o overload t he supply socket. Plug-in ada ptors are

not approved. In some areas special electrical hazards

exist, a qua rium laborat ories for example, and it is

desirable for sockets to be fed via high sensitivity Residual

Current D evices (RCD s) - previously know n a s Earth

Leakage Circuit Breakers (ELCBs) - (References 7 and 9).

Installation of fixed RCDs is carried out by the Estates

Office.

5.2Plugs

Mains supply plugs must be in good condition (no cracks

or pieces missing) correctly wired, appropriately fused and

the supply cable outer sheath clamped inside the plug

between non-conductive faces (References 6 and 10). Any

plugs that are damaged beyond repair must be thrown

aw ay t o ensure that t hey are not re-used.

Plugs and sockets for use at differing voltages must be

non-interchangeable, ie it must not be possible to use a

plug for one voltage level with a socket having a different

voltage source.

All mains electrical plugs must conform to the relevant

British Standard (Reference 3)

square 3-pin 13a to BS 1363

round 3-pin 5a a nd 15a to BS 546

round 2-pin 5a to BS 4573

industrial plugs for single and 3-phase use to BS 4343and

appliance connectors to BS 4491, etc.

Where plugs are routinely and regularly connected and

reconnected ma ny times during a da ys w ork, eg vacuum

cleaner plugs etc, it is prudent to use a rubber moulded or

durable (eg nylon) plug. Damaged plugs must be repaired

or replaced a s soon as the dama ge is noticed. A poster

reminding staff and students of this requirement is

available from Safety Services.

The IEC and old BS colour codes for wiring plugs are

Terminal IECColour Code Old BSColour Code

Earth (E or ) Green/Yellow formerly Green

Live (L) Brown formerly Red

Neutral (N) Blue formerly Black

Special care must be taken by laboratory supervisors and

Departmental Safety Officers to familiarise overseas staffand students with these colour codes.

A plug must be provided and used for each item of

electrical equipment; it is not permissible to connect two

or more items of equipment to the mains supply using one

plug, nor one item using tw o plugs. Equipment should be

isolated by the removal of on e plug.

5.3Plug Fuses

A fuse is a device for opening a circuit by means of a fuse

element that melts when the current exceeds a

predetermined and stated value. The cartridge fuse rating

to be used d epends on the current car rying capability of

the input mains cable and t he power requirement of t he

equipment, w hich is normally stamped on the case or

chassis, as shown in the table in Section 5.5. The cartridge

fuses used in square three-pin 13a plugs must comply with

BS 1362.

Where the main load in a piece of equipment is an electric

motor d ue consideration should be given to allow for t he

power surge encountered when the unit is turned on. An

electrician should be consulted when necessary. In some

instances anti-surge fuses may be required. When fuse

ratings ha ve to b e increased d ue to loa d cha racteristics the

cable current rating must be increased accordingly if

necessary (see table in Section 5.5) so that the fuse and

cable are thermally matched. The practice of w rapping

silver paper or fuse wire around a blow n cartridge fuse or

inserting any other conductor, such as a bent hairpin or

any form o f ma keshift fuse, is highly dangerous and

forbidden. Electrically over-sized fuses must not be used;

the fuse rating must be appropriate to t he demand of the

equipment.

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5.4Connecting Plugs to Cables

Ca re must be ta ken w hilst stripping the insulation from a

cable prior to connecting a plug (or other electrical

component), firstly not to cut t hrough the core conductor

insulation w hilst removing t he outer sheath insulation,

secondly, to remove only the minimum length of core

conductor insulation necessary t o ma ke connection to the

plug pin terminals, and thirdly, not to sever strands of

core conductors so as to decrease the cross-sectional area

and current carrying capacity of the conductors. Ideally an

insulation stripping tool should be used for these

operations.

Before a plug is connected the cable core wires must be

twisted so that there are no unattached or protruding

strands of conductors inside the plug that ma y make an

electrical path to t he outside of th e plug or t o ot herterminals inside the plug. All terminal screws must be

tight and the cable clamp must grip the outer sheath of

the cable fi rmly. The live core conductor should be

connected to the live pin terminal using the shortest length

of core conductor possible and the neutral and earth core

conductors connected leaving some slack inside the plug.

This procedure ensures that if the cable is wrenched out of

the lug the live core conductor is disconnected before the

earth and neutral. Two-pin plugs must not be connected

to three-core cables. When connecting two-core cable to a

three-pin plug the earth terminal must not be used and the

screw on the earth terminal should be tightened to prevent

it falling out.

5.5Flexible Cables

Ca bles from plugs to equipment must be of a dequate duty

to carry out t he required current, unknotted, ad equately

insulated, free from visible damage such as cracks, frays

and kinks and long enough to be used without stretching

or causing a trip hazard.

Where cables are damaged or perished and require

replacement the cables and plug fuses shown in the table

below must be used.

When a cable following the old BS colour code of green,

red and black is to be replaced it must be replaced with

yellow/green, brow n and blue cored cable to IEC

specification. H ow ever, it is not manda tory to replace all

old type cables unless they are in poor state of repair.

Equipment fitted with a cable that does not conform to

either of these two codes, for example, overseas

equipment (References 10 and 11) must be rewired with

yellow/green, brow n a nd b lue core cable before it is used

at the University. It is importa nt to note tha t green/yellowcolour coded wire must only be used fo r earth conductors

and no other purposes. Details of overseas power supplies

are given in Reference 12.

Equipment Maximum Cable Conductor Fuse Cable

Power Current Current CSA Rating Core

Consumption at 240V Rating Resistance

Up to 450W 1.88a 3a 0.5mm2 2 or 3a 0.040ohms/m

450W-700W 2.92a 3a 0.5mm2 3a 0.040 ohms/m

700W-1.1kW 4.58a 6a 0.75mm2 5a 0.027 ohms/m

1.1kW-2.2kW 9.17a 10a 1.00mm2 10a 0.020 ohms/m

2.2kW-3.0kW 12.50a 13a 1.25mm2 13a 0.016 ohms/m

CSA cross sectional area

Flexible cables and plugs from sockets to equipment must

be by single plug and cable only, ie parallel feeds by any

method a re prohibited.

Cables should be insulated, sheathed, of appropriate size and

type, as short as practical (preferably not exceeding 2 metresin length), and located so as to prevent danger or damage. In

cases where cables exceeding 2 metres in length a re needed

repeatedly or semi-permanently then the provision of

additional fixed outlets should be sought. Flexible cables

must NOT be permanently fixed within or outside a building

ie they must not be used as permanent wiring.

5.6Joining Cables

The practice of joining short lengths of cable together to

make a longer cab le by either tw isting/soldering core

conductor together and insulating the joints using

sellotape or insulating tape, or by using terminal blocks is

forbidden. Ideally one continuous length of cable should

be provided. However, if the joining of lengths of cable is

unavoidab le, a suitab le cable connector confo rming to BS

562, BS 3283, BS 4343 or BS 4491 must be used

(Reference 3).

Ca re must be ta ken to ensure that each section of ca ble

has the same number of conductors a nd tha t identical

conductor colour coding (continuity) is maintained

throughout. Tw o-pin connectors that permit continuity

reversal must not be used. G reat care must be ta ken to

ensure that the female section of the cable connector is

connected to the mains supply section of the cable;

connection of the male section could result in live

connector pins being exposed when the cable connector is

disconnected. If routine disconnection is not required, a

non-disconnectable connector should be used.

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5.7Extension Cables

Extension cables (fly-leads) must be kept as short as

practicable and must be fitted with a fuse appropriate to

the maximum current carrying capa city of the cab le.

Unless extension cables are made for a specific purpose,

they should a lwa ys be constructed of 13a cable so that it

is unlikely that they w ould be overload ed during normal

use when connected to a 13a (square pin) socket. Heavier

duty cable may be needed for extension cables used in BS

4343 plug/socket systems.

Whenever reasonably practicable the use of mains

extension cables should be avoided. If two extension

cables are used in series, care must be taken to ensure that

both cables have the same number of coreconductors and

that continuity is maintained. When extension cables are

used the rules made in Section 5.5 must be observed andparticular care must be taken not to pa ss cables through

puddles, in the vicinity of sinks, liquids or other damp

situations. The use of twisted rubber fabric-covered cable

is forbidden; double-insulated cable must be used. The use

of cable connectors in such areas is prohibited. It must

also be remembered th at many aq ueous solutions, such a s

sodium chloride solutions, have a high conductivity a nd

are therefore more dangerous than w ater.

Unprotected cables must not be passed through d oorw ays

which may cause damage to the cable. Cables must not be

passed across laboratory gangways unless they are

protected by Vulcascot (or R S equivalent) to a void trips

and falls. Whenever possible cable should be secured in

out of the way positions.

Extension cables should not be tightly coiled whilst in use

in case local heating occurs whilst heavy currents are used;

reels should be unreeled before use unless used at

negligible load.

5.8Connection of Cables to Equipment

Ca bles must be correctly connected and anchored inside

the equipment, an insulating grommet fi xed around t he

point of entry through the case into equipment w hen

necessary, eg into metal cased (Class I) equipment, and the

earth conductor must be connected to the case (if metal or

conductive) of equipment that is not all-insulated (Class

IIA) or do uble-insulated (C lass IIB). The cable sheath

should be secured inside the equipment by non-conducting

faces so that it cannot slip. When necessary devices to

increase the bending rad ius at the point o f entry should be

used.

In certain circumstances heat resistant cable and special

connectors for termination a t hot terminals may b erequired.

Where the supply cable is connected to the equipment

using a plug and socket, the socket with male pins must

be atta ched to the equipment and t he female plug att ached

to the cable so that plug pins at t he mains voltage cannot

be exposed. In addition, female cable plugs should be

clamped to the outer sheath of the supply cable using a

tool. Some versions of the Bulgin plug do not conform to

these requirements and should be replaced with a IEC

approved connector. In some instances cables are used to

carry power from one item of equipment to another. Care

must be taken to ensure that the connecting plugs and

sockets are arranged so that there is no possibility of live

pins being exposed if any section of the circuit is

unplugged whilst the mains supply is still connected, that

is, exposed pins must always be on the equipment being

supplied - never on the supply cable. Care must be also

taken to ensure that earth continuity is maintained inthese systems.

5.9Equipment Insulation

Equipment must have suffi cient insulat ion between all live

parts a nd external surfaces to prevent a ccess in normal

service and leakage currents. The internal insulation of

electrical equipment is usually governed by the designer or

manufa cturer of the equipment. If equipment fa ils the

internal insulation test (Section 7) it must be returned to

departmental workshops, Estates Office Maintenance

Department, the suppliers, or a reputable electrical repair

fi rm for repair.

5.10 Ventilation and Cooling

Some items of eq uipment are pro vided w ith grills and /or

fans to permit adequate passage of air for cooling

purposes. Care must be taken to ensure that cooling grills

are not obstructed. Filters should be cleaned or replaced

according to manufa cturers recommendations.

5.11 Equipment Fuses

Some items of equipment are fitted with internal fuses in

add ition to plug fuses. If an internal equipment fuse blow s

the equipment must be switched off using the equipment

switch (if provided) and isolated from the mains supply

before the spent fuse is removed and replaced. Usually a

blow n fuse is a symptom of some other fa ult. The

equipment should be carefully inspected before it is

returned t o service.

5.12 Disconnection

Pow er should be isolated at the mains supply and plugs

removed from sockets before any work inside equipmentcommences, or any significant modifica tions are made.

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6. TESTING ELECTRICAL EQUIPMENT

All single phase 240v ac mains powered electrical

equipment should b e tested for adequa te earthing,

adequa te insulation, plug a nd ca ble integrity. D etails given

in Code of Practice Testi ng Electri cal Equi pment

(References 1315) may prove useful.

It is difficult to list all the items of University electrical

equipment that requires inspection, testing and labelling.

However, the following list of examples is intended to

illustrate typical items of equipment that should be

included

anglepoise lamps, kettles, drills, hotplates, laboratoryovens, labora tory ha ir-dryers, w aterbat hs, heavy-duty

soldering irons, inspection lamps,

toa sters, vacuum cleaners, flo or po lishers, fl oor

w ashers, electric fi res, heaters, f ood mixers, domestic irons, da rkroom

enlargers, darkroom dryers and glazers, va riacs, etc.

It is most important that all items of portable

equipment are tested because faults in this type of

equipment a ccount for a high proportion of electrical

accidents.

Test a nd inspection procedures vary accord ing to the class,

type and nature (Section 4) of the equipment concerned.

Testing norma lly includes a visual inspection of the

condition of a ll visible parts and the interior of the plug

and fuse, an earth bond test where applicable and a test of

the insulation integrity. However, special care must be

taken not to damage certain sensitive or delicate items

w hilst testing, eg co mputers, electro meters, etc see

Section 4.2 of Code of Practice Testi ng El ectr ical

Equipment.

Fixed, stationa ry a nd porta ble three phase mains

equipment, and equipment operating at currents in excess

of 13a, must not be tested or repaired by departmental

staff. Plug, cable and equipment fa ults noticed by

departmental staff must be reported to th e Estat es Offi ce

Maintenance Department.

7. TESTING RESIDUAL CURRENT CIRCUIT

BREAKERS (RCDS)

The Estat es Of fice Ma intenance Department a nnually tests

RCDs, previously known as Earth Leakage Circuit

Breakers (ELCBs), that a re part o f the mains supply

system for threshold t ripping cur rent and isolation time.

Portable RCDs (Reference 7) should be annually

instrument t ested by departmental staff (Code of Practice

Testi ng Electri cal Equi pment). Where portab le RCD s

are effectively in permanent situ and unlikely to be

dama ged they must be instrument tested annually a ndotherwise monthly. Any case of do ubt should be

instrument t ested forthw ith.

Supervisors of RCD protected areas described in Section

10.2 must arrange the testing of the RCD test button at

the start of each working day. However, in areas where

live work is not carried out, for example, process areas

w here continually running plant or equipment a re

protected by RC Ds, t he test b utton need only be tested

on a monthly ba sis so as not to unnecessarily interrupt the

supply and create a nuisance.

8. EXPERIMENTAL EQUIPMENT

It is impossible to describe all the potential electrical

haza rds that may o ccur w hen experimental equipment is

constructed for research purposes. However, the points

made in Sections 4, 5, 6 and 7 should be followed

whenever reasonably practicable to reduce risks to a

minimum. An annual inspection and test should bepossible providing the precautions regarding the testing of

sensitive and/or delica te electro nic equipment d escribed in

Code of Practice Testi ng Electri cal Equi pmentare

observed.

8.1General Points

G eneral points to note regarding experimenta l equipment

are as follows

Short Cuts

One of the main hazards to avoid is the temptation to

take short cuts to obta in a quick result. Experiments

should always be carefully planned in advance, the

haza rds assessed a nd a ppropriate precautions ta ken. In

cases of doubt Supervisors, D epartmental Safety O ffi cers,

Safety Services or the Estates Office should be approached

for help and a dvice.

O perati on at Low Safe Vo ltages

Whenever reasonable practicable equipment should be

designed to operate below 50v ac or 120v dc.

Colour Codes

Ma ins supply cables must alw ays be connected to IEC

standa rds (Sections 5.4 a nd 5.8) and green/yellow colour

coded conductors must only be used for earth conductors;

the use of green/yellow for any ot her connection is

forbidden. G reen conductors may o nly be used for non-

earthing purposes as a part of spectrum colour coded

multi-cables of at least five other colours.

D esign t o BS Specifications

Whenever reasonably practicable BS 3456 and BS

Specifications (Reference 3) should be followed.

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8.2Live Work

No live w ork is to be done until a risk assessment ha s been

completed and the significant findings recorded in writing

and brought to the attention of the relevant people. The

following points must be noted before embarking on live

w ork.

Isolation

Equipment should alw ays be isolated from the mains

supply before internal adjustments, maintenance or

overhauls that do not require the application of mains

pow er, are carried out. If live testing or adjustments

have to be carried out , precautions must be ta ken by the

provision of shrouding etc to avoid a ccidental contact

with exposed live terminals. Work of this nature must not

be carried out alone and the highest possible degree of

supervision must be provided for undergraduate studentswho may be involved in this type of activity. Only

qua lified trained personnel may undertake this type of

work.

Maintenance of X-Ray generators and similar high voltage

power supplies require particular caution in both physical

and electrical examination.

Clear Work A rea

The working area must be kept clear of items left on the

floor that may cause someone to trip and fall onto live

teminals (where exposed live terminals can be justified).

The equipment must also be secure on the work surface so

that it does not move unexpectedly.

Equipment L eft O perating Unattended in a D angerous

Condition

Equipment must not be left unattended while it is in a

potentially dangerous exposed state. In some instances the

erection of physical barriers may be necessary to prohibit

unauthorised access to a reas where this type of a ctivity is

being carried out. There are occasions when test

equipment is required to operate witho ut earthing.

Authorisation must be sought from the Laboratory

Supervisor, D epartmental Safety O fficer or H ead of

Department for w ork of this nature and a RC D

incorporated in the mains supply. Electrical hazard signs

should be displayed w here necessar y.

M at Sw itches

Ma t switches are available to place under mats located in

the paths of access to equipment that is left running in a

dangerous condition. The weight of a person w alking on

the mat isolates the equipment before he could touch any

parts. These switches must be used in a manner that

requires positive manual re-activastion, ie when a person

steps off th e mat th e equipment must not be a utomat icallyreconnected to the supply.

M ains Power Supplies to E lectr onic Equi pment

In a high proportion of electronic equipment the majority

of components operate at less than 12v dc a nd the only

electrical hazard a t voltages of greater than 50v ac is the

mains supply to the mains step-down transformer.

Consequently it is desirable when wo rking on the low

voltage components to cover the mains tra nsformer

teminals and other components on the primary side of the

transformer to prevent accidental contact with hazardous

supply voltages. Permanent shrouding should be provided

where such activities are frequently necessary in teaching

classes etc.

8.3Trials of Prototypes

Equipment should alw ays be isolated, by means of a

suitable switch, and disconnected from the mains supplybefore internal adjustments, maintenance or overhauls

that do not require the application of mains power, are

carried out. If live repairs or ad justments have to be

carried out, great care must be taken to avoid a ccidental

contact with exposed live terminals (References 15 and

16). Wherever possible an isolation transformer or

portable RCD should be used.

8.4Isolation Switches

Isolation switches must be located in an easily accessible

position a nd clearly labelled so that they can be easily a nd

safely reached and operat ed in an emergency. Recessed

switches should be used if accidental isolation could cause

a hazard.

8.5Earth Bonding

Painted metal cases may no t be adequa tely earthed by

merely att aching an earth conductor. The paint should be

scraped aw ay in the vicinity of t he connection and/or a

star w asher fit ted to ensure good contact. G enerally the

earth bond resistance should not exceed 0.1 ohms.

However, an earth bond resistance up to a maximum of

0.5 ohms is acceptable on the basis indicated in Section

5.5 for some items of equipment tha t a re fitted w ith long

mains supply cables.

8.6Protection of Cables against Mechanical Damage

Mains supply cables should not be positioned in a

location w here they could be mechanically dama ged by

cog-wheels, blades etc. If such siting cannot be avoided

earthed amour-based cable should be used on mains

supplies or the supply voltage reduced to 12 or 24v.

H ow ever, the use of low er supply voltages demands th euse of higher currents for a ny given pow er consumption,

and care must be taken to ensure that the cable used is of

sufficient dut y to carry the currents involved.

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8.7Internal Fuses

Equipment fuses must be installed on the live side of the

supply and aft er the equipment isolation sw itch in the

supply circuit. Before replacing a blow n eq uipment fuse

the equipment isolation switch must be off and the

supply plug removed from the electrical supply socket.

8.8Insulation

When designing and constructing single phase mains

supplied experimental equipment, it is advisable to

provide internal insulation between live and eart h of at

least 500 kohms or preferably 1 Mohms whenever

possible. Ho w ever, this is not alw ays practicable for some

items of equipment, such as furnaces and ovens, because

aerial moisture absorption markedly decreases the

resistance of many porous refractory ma terials.

8.9Exposed Terminals

Terminals carrying vo lta ges of 50v or mo re should be

insulated or protected t o prevent accidental contact.

Ho w ever, providing the permission of the Departmental

Safety Officer or research supervisor is obtained in

advance and the operator is not working alone, proto-type

equipment may be operated with live terminals exposed,

but not unatt ended. Immediately follow ing initial trials,

the equipment must be ad equa tely protected and /or

insulated before it is placed in routine operat ion. The

precautions and procedures described in References 15

and 16 may be of use to persons involved in this type of

activity.

Ca re must be ta ken to cover tra nsformer terminals

(Section 5.9).

8.10 Interlocks

In some situations the fitting of interlock switches to

equipment side pa nels and covers is necessary (References

17 and 18). These swit ches aut oma tically isolate the

ma ins supply if a panel is removed. Ca re must be ta ken

to use interlock switches that fail-to-safety so that

interlock failure does not create an unexpected dangerous

situat ion. Interlocks must be regularly tested (Reference

17) and circuitry should be designed to fail-safe (BS

5304).

8.11 Non-Standard Supply Voltages, Plugs and Sockets

Equipment operating a t volta ges other than 240v, for

example 110v eq uipment, must be fit ted w ith plugs and/or

sockets that ca nnot b e connected to the norma l mains

240v supply (Section 5.2).

8.12 Transformers

G reat care must be taken when connecting any

transformer because errors can lead t o very high volta ges

being prod uced unexpectedly. In cases of doub t, ad vice

must be sought before connection and use.

I solation Tr ansformers

Safety isolation t ransformers or transformers with the

secondary centre tapped to earth w ith an earth screenbetween primary a nd seconda ry w indings can provide

useful protection against electric shock, eg 110v centre

tapped to earth supplies for ha nd too ls and isolation

transformers on some electronic apparatus (References 15

and 19).

Ideally, isolation transformers should be encased or

enclosed w ithin equipment a nd to appropriate BS and IEC

specifica tions. These items should be tested as separa te

items with pa rticular a ttention to case and core

protection. Sockets should be to BS 4343 on the isolation

side and output volta ge rating clearly identified.

Variacs

The connection of variacs (variable autotransformers)

pose a pa rticular da nger. Whenever mains cables of

variacs are replaced care must be taken to ensure that:

particular care is taken to distinguish between inputand output terminals

the neutral conductor to the supply cable is connectedto th e terminal wh ich is common to bo th the input

and output of the variac

the live supply (not neutral) is fused

equipment whose maximum safe input voltage is lessthan the maximum output of a variac is not directly

connected to the variac.

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8.13 Capacitors

Ca pacitors can store large a mounts of electrical energy

and care should be taken to short circuit capacitors with a

suitable resistance before the terminals or wires leading to

them are touched. In some circumstances bleed resistors

or dump sw itches may b e necessary to a utomat ically

discharge capacitors w hen the supply is turned of f a nd a n

earthing rod provided for operators to manually earth

capa citors before touching. The potentia l electrical

hazards posed by capacitors must be assessed bearing

mind both t he operating potential (v) and capacity (C)

from which the stored energy (E) can be calculated from

the relationship E = 1/2Cv 2. These precautions may not

be required at vo ltag es below 50v ac or 120v dc. The

discharge of 0.25J of stored energy to the human bod y

can provide a heavy shock and 10J can be fatal.

Capacitors of hazardous capacity should be individuallykept short-circuited with an appropriate resistor during

storage. Ca re should be taken to avoid the danger of

burns from high va lue capa citors.

8.14 Batteries and Accumulators

Experiments and equipment involving the use of batteries

pose ha zards. Some ba tteries can become lethal if

exposed to short circuits. O thers can evolve reacta nts

w hich are explosive and can easily be detona ted by sparks

or other sources of ignition. Ca re must be taken not to

allow gases and vapours to accumulate, and to prohibit

activities, such as smoking, etc that may provide a source

of ignition. In addition, metal bracelets, metal w atch

straps, rings, etc must not be worn w hilst ha ndling

secondary cells because accidental terminal contact may

cause such items to become welded to the terminals thus

permitting the fl ow of high currents through the bra celet

etc and results in severe burns. Suitable protective

clothing including full face visors and gloves should be

w orn when handling or working with batteries. Eye w ash

must be readily ava ilable. Lead-acid bat teries should

alw ays be mounted in stab le carrying boxes or other

suitable equipment provided. A sign should indicate

charging rate and potential. Ensure that t he charger is

turned off before disconnecting cables to a void the da nger

of sparks igniting gases.

L ithium Cells

Lithium cells are liable to explode if recharged. Such cells

are commonly used in memory storage systems and care

must be taken to ensure that they are not connected in

series with other cells.

8.15 Water Flow Systems

If a n item of electrical equipment also contains a w ater

flow system great care must be taken to keep these

services as far apart as possible inside the equipment and

all practicable steps such as using hose, collar or jubilee

clips, hose of suitable duty etc, must be used to avoid

water leaks. The practice of securing a water supply hose

to a glass or metal w ater supply or exhaust tub e by tightly

tw isting a length of w ire around the joint is forbidden

because the wire may cut through the supply hose and

cause a leak. It is advisable to locate water systems below

electrical circuits inside and outside equipment whenever

practicable so that if a water leak occurs water cannot

flo w dow n over electrical circuits an d connections.

The use of rubber hose for water circuits is undesirable

because rubber will eventually perish and cause a leak.PVC or braided nylon hose, for example, should be used.

Co nnections in the w ater circuits must not b e made

directly above electrical connections. In certain wet work

areas, such a s aq uarium labo rato ries (Section 10.4),

greenhouses with spray watering systems etc, it is worth

w hile fit ting w ater proof ed mains supply sockets and

plugs and a Residual Current Circuit Breaker (Sections 5.1

and 7) to the circuit supply so that if a current leakage to

earth o ccurs the main supply is automa tically isolated

(References 7 and 9). D etails of portab le RCD s are

ava ilable from the Estates Of fice. Requests for fi xed

RCCB installation should be sent to the Estates Office.

Whenever possible fixed RCDs should be used so that all

appliances fed by the circuit are protected.

8.16 Furnaces

Ca re must be ta ken w hen constructing furnaces to provide

adequa te internal a nd external electrical insulation a nd it

should be borne in mind tha t the insulation a fforded by

many refractory ma terials decreases markedly a s the

temperature increases. Consequently insulation tests

(Saf ety G uide Testing Electrical Eq uipment) should be

carried out w ith the furnace at operating temperature. The

use of metal tongs to handle hot items when a furna ce is

operating can a lso lead to electric shocks and great care

should be taken to design equipment and systems of w ork

that preclude this possibility (Reference 20). Heat resistant

cable and special hot terminal connectors will frequently

be required in this type of w ork.

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8.17 Explosion Protection in Highly Flammable

Atmospheres

Electrical equipment that may provide a source of ignition

should not be placed in areas such as fume cupboards

where solvents are in use that may generate a highly

flammable atmosphere. Conversely sources of highly

fla mmable vapour must not b e used or stored in the

vicinity of electrical equipment whilst it is operating

(Reference 21). Explosion Hazard signs must be posted

on the doors of all laboratory refrigerators which are not

specially constructed or modified to render them safe in

this respect. Spark-Proofed signs should be posted on the

doors of units that met this requirement.

8.18 High Voltage Work

Staff and students designing or working with HighVoltage (650v 3kv) or Extra High Voltage (>3kv)

equipment are advised to read Reference 22.

8.19 Fieldwork

Certain field activities, such as electrical fishing, working

near overhead nationa l grid or ot her high voltage lines,

excavating near mains services, using petrol engine power

generators, etc require special precautions. Any relevant

Codes of Practice (Reference 23) should be consulted and

the project discussed with the Area Safety Officer before

practical work commences.

8.20 Buzz Plugs

In some instances it is important to receive warning if the

mains supply to an item of equipment fa ils, for example,

the storage of cultures in refrigerators etc. 13a Buzz

Plugs can be obtained that give an audible warning if the

pow er fails.

8.21 Electrostatic Hazards

Some research work may involve use of insulating

materials that present electrostatic hazards (References 24

and 25).

8.22 Thermal Cut-Outs

Co nsideration should be given to installing thermal cut-

outs to the supplies of experimental equipment when

necessary so that the supply is isolated if a pre-set

da ngerous temperat ure is exceeded.

9. MISCELLANEOUS EQUIPMENT

The following comments may prove useful for certain

miscellaneous items of equipment.

9.1Light Bulbs

The replacement of a spent light bulb must not be carried

out whilst power is applied to the light bulb socket in case

the bulb shatters during withdrawal or insertion and

causes a live filament to touch or puncture a persons hand

and deliver an electric shock. After isolating the bulb from

the supply it should be w rapped in a cloth to protect the

hand and eyes in case it should shatter during withdrawal.

Care must always be taken when changing light bulbs to

avoid being knocked from step ladders and hop-ups when

working near doors.

Bulbs provided around theatrical make-up mirrors should

be protected (by a wire mesh cage cover(s) for example) so

that persons cannot f all on the bulbs or inadvertently

touch the socket termina ls from w hich spent bulbs may

have been removed but not replaced.

9.2Audio-Visual Aids Equipment

Useful information relating to the maintenance and use of

aud io-visual equipment is given in Reference 26.

9.3Electrophoresis

The lids of electrophoresis tanks should be fitted with

interlock switches that automatically isolate the supply if

the lid is lifted during use. Where possible resistors should

be fit ted in the supply to limit the maximum current too

about 1 ma.

9.4Power Washers

Details of the safety requirements relating to the use of

power washer are given in Reference 27 and Section 10.5.

9.5Construction Site Equipment

Details of the safety measures to be employed when using

electrical equipment during construction work is given in

Reference 19 a nd Section 10.6.

9.6Foreign Equipment

Overseas equipment purchased from domestic sources

overseas that is not w ired to IEC colour codes (Co de of

Pra ctice Testing Electrical Equipment) must be rew ired

to IEC standards before it is used at the University.

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9.7Overseas Power Supplies

Several overseas types of mains supply packs or battery

rechargers (that contain a step-down transformer and

rectifier to transform the mains AC voltage to an

appropriate D C supply) for use with porta ble instruments

are fitted with live and neutral supply pins that do not

exactly fit a sta ndard UK 13a socket. Such items should

be rehoused in a combined 13a plug an d ma ins power

supply ca se.

10.HIGH RISK AREAS AND ACTIVITIES

An above average risk of electric shock is presented to

staff and students who work and study in certain areas of

the U niversity.

Examples are staff employed to construct a nd ma intain electrical

and electronic equipment in workshops and

laboratories

staff and students involved in teaching electricalengineering a nd electronics

staff and students involved in teaching and research inaq uaria or a nimal houses or greenhouses where

animals, plants etc are maintained and w ater is used in

close proximity to electrical equipment.

In view of the increased risk in these areas the following

preventative measures must be taken.

10.1 General Points

Where wo rk in w orkshops or labora tories involves

operations on live systems in which the nature of the

investigation necessitates w orking w ith ba re conductors,

normal saf ety precautions w hich prevent danger should be

followed whenever practicable (Section 4). In

circumstances where there is no alternative to deviation

from sta ndard practice, it is essential tha t precautions to

avoid danger (section 4) are strictly observed. However,

such precautions are not adequate to avoid danger from

high voltage (above 650v) systems. At high voltages there

is increased risk of death from shock by conta ct and also

the possibility of shock from spark-over on close

approach to bare conductors.

10.2 Electrical and/or Electronic Workshops

Workshops used for repairing, modifying, constructing

and testing electrical or electronic equipment must have a

RCD or isolation transformer fitted to the mains supply

(not battery powered and separate safe low voltage

supplies). (References 7 and 9). The w orkshop supervisor

must check the operation of the RCD by operating theTEST but ton every w orking day before wo rk

commences.

If a ny live chassis w ork is carried out, an Earth Free

Area must be provided. Any rubber mats used must be

tested annually for adequate insulation and details

recorded. Testing should be carried out if damage by the

impregnation of metal swa rf, for example, is noticed. The

use of externally earthed extension cables in the earth free

area t hat are connected to a supply socket outside the area

is forbidden.

10.3 Electrical Engineering Laboratories

Laboratories used for teaching electrical engineering

(Reference 28) pose a particularly high risk due to the

high voltages used, the need to observe functional parts of

generation devices during operation, and inexperience of

the students involved who nevertheless need to gain

adequate experience to obtain due professionalcompetence. In the circumstances those involved must

read R eference 28, a w ritten safe system of w ork (working

procedure) compiled from a risk assessment, must be

estab lished and the following provisions made and

procedures followed.

Provisions

All pow er supplies to appara tus w here voltage abo ve50v ac or 120v dc may be exposed should be provided

from a system tha t is entirely separa te from the

general services and lighting circuits and should

originate from a single circuit breaker so t hat all

supplies excepting lighting can be isolated in an

emergency.

Main and sub-circuits should be adequately protectedby fusing against over-current.

A clearly labelled emergency isolation button(s)located in a convenient place(s) that is easily accessible

from a ll working areas, must be provided to isolate all

the apparatus supply circuits except lighting in the

event of an emergency arising.

Outlet points for the connection of research andexperimental appara tus and other systems should be

arra nged so tha t connections which a re electrically

safe can o nly be mad e without exposure to electrical

danger. Acceptable methods include plugs and sockets

w hich are not interchangeable with th ose used for

general service distribution, safe block connections, or

switches with the ha ndle interlocked to a cover w hich

protects fixed terminals.

Bare conductors at less than 650v that need to beobserved during use must be covered by transparent

covers (eg perspex) to prevent anyone falling on them.

Any appara tus involving the use of bare conductors atgreater than 650v must be placed in a segregated

enclosure that has a n interlocked isolation switch onthe door and a portable earthing rod provided within

the enclosure which is applied to bare conductors

before they are touched aft er isolation.

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An Authorised Entry Only sign must be displayed onthe door(s) to t he laborat ory.

All benches should be non-conductive and areas wherelive conductors at abo ve 50v ac or 120v dc may be

exposed should be surrounded b y a clear and

unobstructed pa ssagewa y. A minimum clearance of a t

least 1 metre is recommended. In the case of adjacent

benches and/or a reas the separa tion recommended is

1.5 metres. Small non-conductive barriers should be

provided betw een ad jacent bench w orkstations to

prevent inadvertent contact w ith neighbouring live

parts.

Instructions on the treatment of persons suffering fromelectric shock shall be prominently displayed in all

labora tories, or parts thereof, w here there is exposure

to da nger at voltages abo ve 50v ac and 120v dc.

Those in charge must be able to render artificialresuscitation should it be necessary.

A telephone must be readily available to summon anambulance.

An insulating device to pull someone off a liveconductor, ie an insulated skipping rope w ith long

w ooden ha ndles must be readily a vailable.

In general, all experimental and test rigs should bedesigned to ensure that there is exposure of bar metal

live at vo ltages above 50v ac an d 120v dc w here it is

necessary to apply test probes, etc for measurement

purposes. If any particular experiment or research

involves an abnormally high degree of risk of shock to

earth, the supply should be made through a safety

isolating tra nsformer with a n unearthed secondary or,

if for any reason that is technically impracticable,

through a high sensitivity RC D.

Procedures

Only persons authorised by the Head of Department may

enter and w ork in the labora tory. Such persons are

qualified electrical engineers, and providing they have

att ained the age of 18 years a nd ha ve been properly

instructed in the avoidance of the dangers of electricity,

electical undergraduate students in their second or

subsequent years, postgradua te students or technical staf f

w orking to t he directions of t he Labora tory Supervisor.

The laboratory must be kept locked when unattended if

these are bare live conductors at dangerous voltages.

No person except a n a uthorised person should carryout w ork on research or experimental a pparat us and

systems where there are conductors exposed when live

at volta ges above 50v ac and 120v dc and no-one

should do such w ork unaccompanied. Students or

technical staff under the age of 18 may, ho w ever, be

trained in car rying out such wo rk provided they are

under the close, immediate and continuous supervisionof a n a uthorised person.

No work should be done on any conductors ofappara tus or systems operating at or generating

voltages above 650V unless the conductors have been

mad e dead a nd efficiently earthed. This restriction

shall not apply to non-lethal HV systems (eg EHT of

TV sets, electrostatic apparatus, pressure test sets, etc)

w here the current availability is below 5 ma.

All labora tory equipment (fixed o r porta ble) should beidentified in a register and regularly checked. A defect

reporting and clearance procedure should be

established to ensur that maintenance needs are

promptly recorded and that defective equipment is not

returned t o service.

10.4 Aquaria

The mains supply circuits of aq uaria should be fitted w ith

a RC D (References 7 and 9) and w ater-proofed supply

sockets provided. Any other connections must be made at

least 30 cm (1 ft) above the highest tank water level in thelaboratory and joints sealed in resin for waterproofing if

necessary. The operation of the RCD must be tested as

described in Section 10.2.

10.5 Power Washed Animal Houses

The supply circuits of animal houses that are power

washed must be fitted with RCDs either on the whole

supply or, if this gives rise to nuisance tripping, on each

individual outlet including those which supply the power

washer. RCD protected 13a plugs must not be fitted to

pow er wa shers. Water proofed outlets or o ther equipment

may be reqired in such areas (Section 8.15). See also

Reference 27.

10.6 Construction Sites and Building Maintenance Work

Portable equipment used on construction sites or during

maintenance work of a compa rable nature should be fed

by 110v ac step-dow n tra nsformers to BS 3535 with the

secondary centre tapped to earth w ith an earthed screen

between primary and secondary windings (Reference 129).

In cases where special equipment can only be used above

110v (eg unavailable as 110v models), the supply circuit

should be controlled by a RCD. Portable handlamps

should be 50v with Eddison Screw lampholders or in

particularly haza rdous situations 25v w ith three-pin

Bayo net Ca p lampholders, in each case supplied by a

Class II tra nsformer to BS 3535. Non -interchangeable

plugs and sockets (Section 5.2) should be used in all

transformer systems and primary leads should be of

minimum practical length. Ca re must a lso be ta ken to

avoid overhead power lines (Reference 23) and identify or

detect und erground mains services (Reference 29). Such

activities must be reported t o the Estat es Offi ce befor e

such work commences on University premises.

10.7 Portable Generators

Safety aspects relating to the use of porta ble generators

are given in Reference 34.

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18/19

1 Eff ects of Cur rent Passing Through a Human Body

IEC Pub licat ions 479/1/1984

2 First-Aid

The Authorised Manual of St John Ambulance

St Andrews Ambulance Associated and

The British Red Cross

3 Bri tish Standards Year Book

British Standards Institute (BSI)

4 Regulati ons for El ectrical Installatio ns

The Institut ion o f Electrical Engineers (IEE),

Edition 16 as amended

5 A Guide to the 16th Edit ion of the IEE W iringRegulations

JF Whitfield, Peter Peregrinus Ltd

6 Flexible l eads, plugs, sockets, etc

G uidance Note GS37, HSE, HMSO

7 EL CB D evelopments in D esign and Appli cations

G E M oore, The Safety Pra ctitioner, M arch 1983

8 The safe use of por tabl e electri cal apparatus (electri cal

safety)

G uidance Note PM32, HSE, HM SO

9 A Gui de to Earth Fault D etection

Merlin G erin

10 Plugs and Fuses

The Electricity Council EC3314

11 Wor ld Electricity Suppl ies

Technical Help to Exporters (THE), Edition 2

12 Businessmans T ravel G uide

Dan Hillman, Cassells

13 Portable Electrical Apparatus

ICI, RoSPA, Publication IS128

14 Electri cal Safety Code for H ospital L aborator y

Equipment

DH SS, H MSO

15 Electri cal Testing

H ealth & Safety Series Booklet H S(G )13, HSE,

HMSO

16 Recommendations for El ectrical Safety i n TV , Radioand Audio Equipment Testing and Servi cing

RETRA

17 Electrical L imit Swi tches and t heir Appl ications

H ealth & Safety Series at Work Booklet 24, HSE,

HMSO

18 Electr ical Safety In terlock Systems

D Hughes, Occupational Hygiene Monograph 2, 1978

19 Constructi on Safety

NFBTE

20 The Electr ical Safety of Resistance H eated L aborator y

Furnaces

I Whitney

21 Electrical I nstallati ons in Flammable Atmospheres

ICI, RoSPA, Publication IS91

22 Safety Precauti ons in the Use of El ectrical Equipment

Imperial C ollege of Science and Technology

23 The Avo idance of D anger fr om O verhead Electric

L ines and U nderground Electri c Cables in For estr y

and Plantations

Forestry Commission

24 Static at Wor k: The Shocki ng Truth

3M United Kingdom

25 Electr ostatic I gniti on H azards of In sulati ng

M aterials

Occasional Paper OP5, H SE, H MSO

26 A Gui de to the Safe H andling and O peration of

Audo-V isual Equi pment

Council for Education Technology (CET)

27 Electrical H azards from Steam/W ater Pressur e

Cl eaners etc

G uidance Note PM29, HSE, HM SO

28 Electr ical Safety i n D epartments of Electr ical

Engineering

G uidance Note GS34, HSE, HMSO

29 Recommendations on the Avo idance of D anger fr om

Underground Electr icity Cables

National Joint Utilities Group

30 Earth M onitoring

LC Ea les and R A Wooda ge, Power & Works

Engineering, September 1977

18 Univers i t y o f H ul l E lec t r i ca l Equipment Sa f e ty G uide Is sued N ovember 1996

REFERENCES


19/19

31 M emorandum on t he Electricity Regulations

Form SHW928, HM SO

32 Safe Use of E lectri city

A Beckingsale and EG Ho oper, RoSPA, Publication

IS73

33 Electr ical Safety in Schoo ls

G uidance Note GS23, H SE, H MSO

34 Emergency Private Generation: Electrical Safety


35 Electrical Test Equipm ent f or use by El ectricians


Amended June 2000

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