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IntroductionThis article looks at temporaryelectrical installations associated withexhibitions, shows and stands. Suchinstallations may be installed indoorsor outdoors within permanent ortemporary structures.The electrical installation of the

building, if any, in which theexhibition, show or stand will takeplace, will not be considered.Currently, there is no Part or Section

of BS 7671: 2001 (2004) coveringexhibitions, shows and stands.Information can be found inIEC 60364-7-711 and HD 60364.7.711in addition to Guidance Note 7.It is proposed that a new section,

Section 711 - Exhibition, Shows andStands, will be included in BS 7671:2008, The 17th Edition of theIEE Wiring Regulations. The DPC ofBS 7671: 2008 includes Section 711,however, this is subject to change.

DefinitionsThe following definitions are extractedfrom IEC 60364-7-711:

ExhibitionEvent intended for the purpose ofdisplaying and/or selling products etc.,which can take place in any suitablelocation, either a room, building ortemporary structure display orperformance in any suitable location,either a room, building or temporarystructure.

ShowDisplay in any suitable location, eithera room, building or temporarystructure.

StandArea or temporary structure used fordisplay, marketing, sales, etc.

Temporary structureA unit or a part of a unit includingmobile portable units, situated indoorsor outdoors, designed and intended tobe assembled and dismantled.

Temporary electrical installationElectrical installation erected anddismantled at the same time as the

stand or the display with which it isassociated.

Origin of the temporaryelectrical installationPoint on the permanent installation orother source of supply from whichelectrical energy is delivered.

Risks and hazardsThe particular risks associated withexhibitions, shows and stands arethose of electric shock and fire due tothe temporary nature of theinstallation, the lack of permanentstructures, severe mechanical stressesand access to the general public.Note that BS 7671 will apply generally

but due to these increased risks,additional measures are recommended.

Assessment of general characteristicsThe nominal supply voltage oftemporary electrical installations inexhibitions, shows and stands shouldnot exceed 230/400 v a.c. As for d.c, thesupply should not exceed 500 v d.c.between any conductors.

EXHIBITIONS, SHOWS AND STANDSby Mark Coles

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System typesThe standards require that where thesystem earthing is TN it should beTN-S other wise a TT earthing systemshould be used.

Importantly, the following systems areNOT permitted:

TN-CRegulation 8(4) of the ElectricitySafety, Quality and Continuity

Regulations 2002 prevents the use ofcombined neutral and earthconductors in any part of aconsumer’s installation.

TN-C-SBecause of the practical difficulties ofbonding all accessible extraneous-conductive-parts, a TN-C-S(PME) system is not appropriate fortemporary and/or outdoorinstallations.

GeneratorsInstallations incorporating generatorsets should comply with Section 551 ofBS 7671.

Where a generator is used to supplythe temporary installation using a TNor TT system, it must be ensured thatthe installation is earthed, preferablyby separate earth electrodes. BS 7430,Code of practice for earthing, statesthat for independent earth electrodesassociated with the local earthing ofthe star point of generating plant, it isrecommended that the earth electroderesistance should not exceed 20 Ω.For TN systems all exposed-

conductive-parts should be bondedback to the generator. The neutralconductor and/or star point of thegenerator should be connected to theexposed-conductive-parts of thegenerator and reference earthed;see figure 2.

Protection against electric shockProtection against direct contact bymeans of obstacles and protectionagainst indirect contact by non-conducting location placing out ofreach should not be used.

Protective equipotential bondingStructural metallic parts which areaccessible from within the stand shallbe bonded to the main earthingterminal and in more than one place ifthe type of construction does notensure continuity; see figure 3.The CSA should be not less than

4 mm² copper. Guidance Note 3,Inspection and Testing, published bythe IEE, advises that supplementaryequipotential bonding conductorsshould have a resistance of 0.05 Ω,or less.

Residual current devicesCables supplying temporary structuresshould be protected at their origin byan RCD of a residual current rating nogreater than 300 mA.These devices should be of the

Fig 2: Exhibition /show distribution with stand-by generator

Fig 3: Construction does not ensure continuity alone

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S-type for discrimination with RCDsprotecting final circuits downstream,see figure 4.All circuits for socket-outlets rated

up to 32 A and all final circuits otherthan for emergency lighting should beprotected by an RCD with a ratedresidual operating current notexceeding 30 mA.Cables supplying temporary

structures should be protected at theirorigin by an RCD of a residual currentrating no greater than 300 mA.These devices should be of the

S-type for discrimination with RCDsprotecting final circuits downstream,see figure 4.All circuits for socket-outlets rated

up to 32 A and all final circuits otherthan for emergency lighting should beprotected by an RCD with a ratedresidual operating current notexceeding 30 mA.

IsolationEvery separate temporary structure,such as a vehicle, a stand or a unit,intended to be occupied by one specificuser should be provided with theirown readily accessible and properlyidentifiable means of isolation; seefigure 5.Further, each distribution circuit

supplying outdoor installations shouldbe provided with its own readilyaccessible and properly identifiablemeans of isolation; examples of suchdevices are shown in figures 6, 7, and 8.

Protection against fireA motor which is automatically orremotely controlled and which is notcontinually supervised should be fittedwith a manual reset protective deviceagainst excess temperature.Lighting equipment such as

incandescent lamps, spotlights, smallprojectors including all otherequipment or appliances with hightemperature surfaces shall be suitablylocated, guarded and installed.All such equipment shall be

arranged well away from combustible

material to prevent contact.Showcases and signs shall be

constructed of material having anadequate heat resistance, mechanicalstrength, electrical insulation andventilation, taking into account thecombustibility of exhibits in relationto the heat generation.Stand installations containing a

concentration of electrical apparatus,lighting fittings or lamps liable togenerate excessive heat shall not beinstalled unless adequate ventilationprovisions are made, e.g. wellventilated ceiling constructed ofincombustible material. In all cases,the manufacturers' instructions shallbe followed.

Wiring systemsArmoured cables or cables protectedagainst mechanical damage should beused wherever there is a risk of

mechanical damage. Wiring cablesshould be copper and have a minimumcross-sectional area of 1.5 mm², andthey should comply with BS 6007 or asappropriate.Flexible cords should not be laid in

areas accessible to the public unlessthey are protected against mechanicaldamage.

Wiring systems - fireWhere no fire alarm system isinstalled in a building used forexhibitions, etc., cable systems shouldbe either be flame retardant toBS EN 60332-1 or BS EN 60332-3 andlow smoke to BS EN 61034 or single ormulticore unarmoured cables enclosedin metallic or non-metallic conduit ortrunking, providing fire protection inaccordance with BS EN 50085 orBS EN 50086 and providing a degree ofprotection of at least IP4X.

Fig 4: S-Type RCD

Fig 6: RCD Fig 7: MCB Fig 8: Plug and socket-outlet

Fig 5: Identifiable means of isolation

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Wiring systems –electrical connectionsJoints should not be made in cablesexcept where necessary as aconnection into a circuit. Where jointsare made, these should be either usingconnectors in accordance with the BS7671, the manufacturer's instructionsor the connection should be made inan enclosure with a degree ofprotection of at least IP4X orIPXXD. Where strain can betransmitted to terminals theconnection should incorporatecable anchorage(s).

Lighting installationsLuminaires mounted below 2.5 m(arm's reach) from floor level orotherwise accessible to accidentalcontact should be firmly andadequately fixed and so sited orguarded as to prevent risk of injury topersons or ignition of materials.In the case of outdoor lighting

installations, HD 384.7.714 applies and

a degree of protection of at least IP33*may be required. The rating IP33means (first digit) protection againstsolid foreign objects of 2.5 mmdiameter and greater and (seconddigit) protected against water sprayingat an angle up to 60° on either side ofthe vertical.

Lighting installations – electricaldischarge lamp installationsInstallations of any luminous tubesign or lamp as an illuminated uniton a stand, or as an exhibit withnominal power supply voltage higherthan 230/400 v a.c. should be installedout of arm's reach or should beadequately protected to reduce therisk of injury to persons. The facia orstand fitting material behindluminous tube signs or lamps shouldbe non-ignitable and protected asrequired by national standards.Controlgear with output voltageshigher than 230/400 v a.c. should bemounted on non-ignitable material.

A separate circuit should be used tosupply such signs, lamps or exhibits,which should be controlled by anemergency switch. The switch shouldbe easily visible, accessible andmarked in accordance with therequirements of the local authority.

VerificationThe temporary electrical installationsof exhibitions, shows and standsshould be tested on site in accordancewith Part 7 of BS 7671 after eachassembly on site. Users should checkthe installation for damage on a dailybasis.

Bibliography and further readingFurther information is available fromthe following sources and publications:

• BS 7671: 2001 (2004) Requirements forelectrical installations

• Guidance Note 3 – Inspection andTesting, Inc AMD No.2 : 2004, IEEPublications

• Guidance Note 7 – Special Locations,Inc AMD No.2 : 2004, IEEPublications

• BS 7430: 1998 Code of practice forearthing

• IEC 60364-7-711 available fromwww.iec.ch

• HD 60364-7-711 available fromwww.cenelec.org

• Electricity Safety, Quality andContinuity Regulations 2002

• HSE Guidance Notes:- Health and Safety at Work etc Act1974 HMSO, ISBN 010 543774 3- Electricity at Work Regulations1989, SI 1989 No 635 HMSO,ISBN 0 11 096635 X- Memorandum of guidance on theElectricity at Work Regulations 1989,HS(R) 25 HMSO ISBN 011 883963 2

Thanks for the images used:Clare Barnes (IET Events)CEE Norm UK LtdMK Electricwww.tlc-direct.co.uk