17th edition iet wiring regulations inspection, testing and certification - brian scaddan

17thEditionIETWiringRegulations

Inspection,TestingandCertification

Fullyup-to-datewiththelatestamendmentstothe17thEditionoftheIETWiringRegulations

SimplifiestheadvicefoundintheWiringRegulations,explaininghowtheyapplytoworkingpracticeforinspection,testingandcertification

Expert advice from an engineering training consultant, supported with colourdiagrams,examplesandkeydata

Thispopularguideclarifiestherequirementsforinspectionandtesting,explaininginclearlanguagethosepartsoftheWiringRegulationsthatmostneedsimplifying.Inadditiontothedescriptiveanddiagrammatictestmethodsthatarerequired,explanationsofthetheoryandreasoningbehindtestproceduresaregiven,togetherwithusefultablesforthecomparisonoftestresults.Thebookalsoprovidesessentialinformationonthecompletionofelectricalinstallationcertificates,withastep-by-stepguideontheentriesthatneedtobemadeandwheretosourcedata.

WiththecoveragecarefullymatchedtothesyllabusoftheCity&GuildsCertificatesinInspection,TestingandCertificationofElectricalInstallations(2394-10and2395-10)andFundamentalInspection,TestingandInitialVerification(2392-10),andcontainingsamplepapersandsuggestedsolutions,itisalsoanidealrevisionguide.

BrianScaddan,IEng,MIET,isaconsultantforandanHonoraryMemberofCity&Guildswithover40years’experienceinFurtherEducationandtraining.HeisDirectorofBrianScaddanAssociatesLtd,anapprovedCity&Guildstrainingcentreofferingcoursesonallaspectsofelectrical installationcontracting including theC&G2382-15,2392-10,2377-22,2394-01,2395-01and2396-01.Heisalsoaleadingauthorofbooksforthesecourses.

17thEditionIETWiringRegulations

Inspection,TestingandCertificationEighthEdition

BrianScaddan

Eightheditionpublished2015byRoutledge2ParkSquare,MiltonPark,Abingdon,OxonOX144RN

andbyRoutledge711ThirdAvenue,NewYork,NY10017

RoutledgeisanimprintoftheTaylor&FrancisGroup,aninformabusiness

©2015BrianScaddan

TherightofBrianScaddantobeidentifiedasauthorofthisworkhasbeenassertedbyhiminaccordancewithsections77and78oftheCopyright,DesignsandPatentsAct1988.

Allrightsreserved.Nopartofthisbookmaybereprintedorreproducedorutilisedinanyformorbyanyelectronic,mechanical,orothermeans,nowknownorhereafterinvented,includingphotocopyingandrecording,orinanyinformationstorageorretrievalsystem,withoutpermissioninwritingfromthepublishers.

Trademarknotice:Productorcorporatenamesmaybetrademarksorregisteredtrademarks,andareusedonlyforidentificationandexplanationwithoutintenttoinfringe.

Firsteditionpublished1996byNewnes,animprintofElsevierSeventheditionpublished2011byNewnes,animprintofElsevier

BritishLibraryCataloguinginPublicationDataAcataloguerecordforthisbookisavailablefromtheBritishLibrary

LibraryofCongressCataloging-in-PublicationDataScaddan,Brian.17theditionIETwiringregulations.Inspection,testingandcertification/BrianScaddan.—8thedition.pagescmIncludesindex.1.Electricwiring,Interior—Safetyregulations—GreatBritain—Handbooks,manuals,etc.2.Electricwiring,Interior—Insurancerequirements—GreatBritain—Handbooks,manuals,etc.3.Electricwiring,Interior—Inspection—Handbooks,manuals,etc.4.Electricwiring,Interior—Testing—Handbooks,manuals,etc.I.Title.II.Title:Inspection,testing,andcertification.III.Title:IETwiringregulations,inspection,testingandcertification.TK3271.S26922015621.319‘24021841—dc232014048613

ISBN:978-1-138-84886-3(pbk)ISBN:978-1-315-72595-6(ebk)

TypesetinKuenstler480andTradeGothicby

ServisFilmsettingLtd,Stockport,Cheshire

ContentsPREFACEINTRODUCTIONCHAPTER1AnOverviewStatutoryandNon-StatutoryRegulationsElectricalSystemsandEquipmentTheBuildingRegulationsPart‘P’InstrumentsCHAPTER2InitialVerificationCircumstancesWhichRequireanInitialVerificationGeneralReasonsforInitialVerificationInformationRequiredDocumentationRequiredandtobeCompletedSequenceofTestsCHAPTER3TestingContinuityofProtectiveConductors(Low-ResistanceOhmmeter)CHAPTER4TestingContinuityofRingFinalCircuitConductors(Low-ResistanceOhmmeter)CHAPTER5TestingInsulationResistance(InsulationResistanceTester)CHAPTER6SpecialTestsProtectionbyBarriersorEnclosuresProtectionbyNon-ConductingLocationCHAPTER7TestingPolarity(Low-ResistanceOhmmeter)CHAPTER8TestingEarthElectrodeResistance(EarthElectrodeResistanceTesterorLoopImpedanceTesters)Method1:ProtectionbyOvercurrentDeviceMethod2:ProtectionbyaResidualCurrentDeviceCHAPTER9TestingEarthFaultLoopImpedanceTesterExternalLoopImpedanceZe

CHAPTER10AdditionalProtection(RCDTester)RCD/RCBOOperationRequirementsforRCDProtectionCHAPTER11ProspectiveFaultCurrent(PFC/PSCCTester)CHAPTER12CheckofPhaseSequence(PhaseSequenceIndicator)CHAPTER13FunctionalTestingCHAPTER14VoltageDrop(ApprovedVoltmeter)CHAPTER15PeriodicInspectionPeriodicInspectionandTesting

CircumstancesWhichRequireaPeriodicInspectionandTestGeneralReasonsforaPeriodicInspectionandTestGeneralAreasofInvestigationDocumentationtobeCompletedSequenceofTestsCHAPTER16CertificationElectricalInstallationCertificateElectricalInstallationConditionReportObservationCodesMinorElectricalInstallationWorksCertificateContentsofaTypicalScheduleofTestResultsScheduleofInspections(asperBS7671)APPENDIX12394SamplePaperSectionASectionB2395SamplePaperSectionASectionBAPPENDIX22394SamplePaper(Answers)SectionASectionB2395SamplePaper(Answers)SectionASectionBAPPENDIX32394/5SampleMCQPaperandAnswersAnswersINDEX

PrefaceThis book is primarily for use as a study resource for the City & Guilds 2394 InitialVerificationandC&G2395PeriodicInspectionandTestingcourses.

However, it is also a useful reference for C&G 2382-15, 17th Edition; C&G 2392-10,FundamentalInspectionandTesting,andC&G2396,Design.

BrianScaddan

IntroductionMany candidates embarking on the 2394 and 2395 courses find difficulty in eitherunderstandingwhattheExaminerisaskingforinquestions,orhowtoexpressthemselveswhenanswering.The samplepapersandanswersat theendof thisbook shouldhelp toalleviatethesedifficulties.

One of the common problems is a lack of understanding of some basic principles andincorrect use of technical wording. In many instances it may be unfair to quote‘misunderstanding’when it is probably just a caseofhaving forgotten thedetails of the17thEdition,etc.

Below is a list of commonwords, phrases and acceptable abbreviations that candidatesreallyshouldbeawareof,astheyoftenappearinexaminationquestions:

StatutoryDocuments

TheHealthandSafetyatWorkAct(H&SWA).Affectseveryoneatwork.TheElectricityatWorkRegulations (EAWR).Affects those atwork involvedwith

electricalsystems. The Building Regulations Part ‘P’.Affects those who install electrical systems in

domesticpremises. TheElectricity Safety,Quality andContinuityRegulations (ESQCR).Thesereally

onlyaffectthesuppliersofelectricalenergytopremises.

Non-StatutoryDocuments

BS7671.TheIETGuidanceNote3(GN3).ThisisspecificallyforInspectionandTesting.TheH&SGuidanceNoteGS38(GS38).Thisdealswithelectricalinstruments,etc.Anyotherdocumentsthatrelatetoinspectionandtesting.

Electrical System This is defined in the EAWR as anything that generates, stores,transmits, uses, etc. electrical energy (e.g. a power station or a torch battery or a testinstrument,etc.).

DutyHolderThisistheEAWRTitleofanyonewhohascontrolofanelectricalsystem.

CompetentPersonThisistheEAWRStatusofaDutyHolder.

BasicProtectionProtectionagainstelectricshockunderfault-freeconditions(touchinganintentionallylivepart)

MethodsofProvidingBasicProtectiononly:

Insulationofliveparts.

Barriersorenclosures.Obstacles(notcommon,onlyforuseunderthesupervisionofskilledpersons). Placing out of arms’ reach (not common, only for use under the supervision of

skilledpersons).

FaultProtectionProtectionagainstelectricshockundersingle-faultconditions(touchingaconductivepartmadeliveduetoafault).

MethodsofProvidingFaultProtectiononly:

AutomaticDisconnectionofSupply(ADS).ThisisEarthing,Bondingandensuringprotectivedevicesoperateinthedesignatedtime.

MethodsofProvidingbothBasicandFaultProtection:

DoubleorReinforcedinsulation.SELVorPELV.ElectricalSeparation(foroneitemofequipment,e.g.shaverpoint).

ExposedConductivePartCasingofClassIequipmentormetalconduit/trunking,etc.

ExtraneousConductivePartStructuralsteelwork,metallicgas,water,oilpipes,etc.

Additional Protection Used in the event of failure of Basic and/or Fault protection orcarelessnessbyusers.

MethodsofProvidingAdditionalProtection:

RCD,30mAorlessandoperatingwithin40msatfivetimesitsratingSupplementaryEquipotentialBonding.

ProtectiveConductors:

TheEarthingconductorConnectstheMainEarthingTerminal(MET)tothemeansofearthing.(TheMainEarthingconductorisincorrectterminology.)

MainProtectiveBondingconductorsConnecttheMETtoextraneousconductiveparts.

CircuitProtectiveconductors(cpc)ConnecttheMETtoexposedconductiveparts. Supplementary Protective Bonding conductors Connect together exposed and

extraneousconductiveparts in locationssuchasbathrooms,swimmingpools,etc.orwheredisconnectiontimescannotbemetalthoughRCDsareusuallyusedinthiscase.

TheIETWiringRegulationsBS7671

Beforeweembarkonthesubjectofinspectionandtesting,itis,perhaps,wisetoexamineinmoredetailsomeofthekeytopicspreviouslylisted.

Clearly, the protection of persons and livestock from shock and burns, etc. and theprevention of damage to property are priorities. In consequence, therefore, thoroughinspection and testing of an installation and subsequent remedialworkwherenecessarywillsignificantlyreducetherisks.

Soletusstartwithelectricshock;thatis,thepassageofcurrentthroughthebodyofsuchmagnitude as to have significant harmful effects. Figure 0.1 illustrates the generallyacceptedeffectsofcurrentpassingthroughthehumanbody.

Howthenareweatriskofelectricshock,andhowdoweprotectagainstit?

Therearetwowaysinwhichwecanbeatrisk:

1.Touchinglivepartsofequipmentorsystemsthatareintendedtobelive.2.Touching conductivepartswhicharenotmeant tobe live, buthavebecome live

duetoafault.

FIGURE0.1Shocklevels.

1–2mA Barelyperceptible,noharmfuleffects5–10mA Throwoff,painfulsensation

10–15mA Muscularcontraction,can’tletgo20–30mA Impairedbreathing50mAandabove Ventricularfibrillationanddeath

The conductive parts associated with the second of these can either be metalwork ofelectricalequipmentandaccessories(ClassI)andthatofelectricalwiringsystemssuchasmetallic conduit and trunking, etc. called exposed conductive parts, or other metalworksuchaspipes,radiators,girders,etc.calledextraneousconductiveparts.

Letusnowconsiderhowwemayprotectagainstelectricshockfromwhateversource.

ProtectionagainstShockfromBothTypesofContact

Onemethodofachievingthisisbyensuringthatthesystemvoltagedoesnotexceedextralow(50Va.c.,120Vripple-freed.c.),andthatallassociatedwiring,etc.isseparatedfromallothercircuitsofahighervoltageandearth.Suchasystemisknownasaseparatedextralowvoltage (SELV). If a SELV system exceeds 25V a.c., 60V ripple-free d.c., then extraprotectionmustbeprovidedbybarriers,enclosuresandinsulation.

BasicProtection

ApartfromSELV,howcanwepreventdangertopersonsandlivestockfromcontactwithintentionallyliveparts?Clearlywemustminimizetheriskofsuchcontact,andthismaybeachievedinoneormoreofthefollowingways:

1.Insulateanyliveparts.2.Ensurethatanyuninsulatedlivepartsarehousedinsuitableenclosuresand/orare

behindbarriers.3.Placeobstaclesintheway.(Thismethodwouldonlybeusedinareaswhereskilled

and/orauthorizedpersonswereinvolved.)4.Placinglivepartsoutofreach.(Onceagain,onlyusedinspecialcircumstances,e.g.

liverailsofoverheadtravellingcranes.)

Aresidualcurrentdevice(RCD)maybeusedasadditionalprotectiontoanyoftheothermeasurestaken,providedthatitisratedat30mAorlessandhasanoperatingtimeofnotmorethan40msatatestcurrentoffivetimesitsoperatingcurrent.

It should be noted that RCDs are not the panacea for all electrical ills, they canmalfunction,but theyareavalidandeffectiveback-upto theothermethods.Theymustnotbeusedasthesolemeansofprotection.

FaultProtection

How can we protect against shock from contact with unintentionally live, exposed orextraneous conductive parts whilst touching earth, or from contact betweenunintentionally live exposed and/or extraneous conductive parts? The most commonmethod is by protective earthing, protective equipotential bonding and automaticdisconnectionincaseofafault.

Allextraneousconductivepartsareconnectedwithamainprotectivebondingconductorand connected to the main earthing terminal, and all exposed conductive parts areconnectedtothemainearthingterminalbythecircuitprotectiveconductors(cpc).Addtothisovercurrentprotectionthatwilloperatefastenoughwhenafaultoccursandtheriskofsevereelectricshockissignificantlyreduced.

Othermeansoffaultprotectionmaybeused,butarelesscommonandsomerequireverystrictsupervision.

UseofClassIIEquipment

Oftenreferredtoasdouble-insulatedequipment,thisistypicalofmodernapplianceswherethereisnoprovisionfortheconnectionofacpc.Thisdoesnotmeanthatthereshouldbenoexposedconductivepartsandthatthecasingofequipmentshouldbeofaninsulatingmaterial; it simply indicates that live parts are sowell insulated that faults from live toconductivepartscannotoccur.

Non-ConductingLocation

Thisisbasicallyanareainwhichthefloor,wallsandceilingareallinsulated.Withinsuchanarea theremustbenoprotectiveconductors,andsocketoutletswillhavenoearthingconnections.

It must not be possible simultaneously to touch two exposed conductive parts, or anexposed conductive part and an extraneous conductive part. This requirement clearlypreventsshockcurrentfrompassingthroughapersonintheeventofanearthfault,andtheinsulatedconstructionpreventsshockcurrentfrompassingtoearth.

Earth-FreeLocalEquipotentialBonding

This is inessenceaFaradaycage,whereallmetalsarebondedtogetherbutnot toearth.Obviously, great care must be taken when entering such a zone in order to avoiddifferencesinpotentialbetweeninsideandoutside.

Theareasmentionedinthisandthepreviousmethodareveryuncommon.Wheretheydoexist,theyshouldbeunderconstantsupervisiontoensurethatnoadditionsoralterationscanlessentheprotectionintended.

ElectricalSeparation

ThismethodreliesonasupplyfromasafetysourcesuchasanisolatingtransformertoBSEN61558-2-6whichhasnoearthconnectiononthesecondaryside.Intheeventofacircuitthatissuppliedfromasourcedevelopingalivefaulttoanexposedconductivepart,therewouldbenopathforshockcurrenttoflow(seeFigure0.2).

FIGURE0.2Electricalseparation.

Table0.1IPCodes

FirstNumeral MechanicalProtection

0Noprotectionofpersonsagainstcontactwithliveormovingpartsinsidetheenclosure.Noprotectionofequipmentagainstingressofsolidforeignbodies.

1Protectionagainstaccidentalorinadvertentcontactwithliveormovingpartsinsidetheenclosurebyalargesurfaceofthehumanbody,forexample,ahand,butnotprotectionagainstdeliberateaccesstosuchparts.

2Protectionagainstingressoflargesolidforeignbodies.ProtectionagainstContactwithliveormovingpartsinsidetheenclosurebyfingers.Protectionagainstingressofmedium-sizesolidforeignbodies.

3Protectionagainstcontactwithliveormovingpartsinsidetheenclosurebytools,wiresorsuchobjectsofthicknessgreaterthan2.5mm.Protectionagainstingressofsmallforeignbodies.

4Protectionagainstcontactwithliveormovingpartinsidetheenclosurebytools,wiresorsuchobjectsofthicknessgreaterthan1mm.Protectionagainstingressofsmall-sizesolidforeignbodies.

5

Completeprotectionagainstcontactwithliveormovingpartsinsidetheenclosure.Protectionagainstharmfuldepositsofdust.Theingressofdustisnottotallyprevented,butdustcannotenterinanamountsufficienttointerferewithsatisfactoryoperationoftheequipmentenclosed.

6 Completeprotectionagainstcontactwithliveormovingpartsinsidetheenclosures.Protectionagainstingressofdust.

SecondNumeral LiquidProtection

0 Noprotection.

1 Protectionagainstdropsofcondensedwater.Dropsofcondensedwaterfallingontheenclosureshallhavenoharmfuleffect.

2 Protectionagainstdropsofliquid.DropsOffallingliquidshallhavenoharmfuleffectwhentheenclosureistiltedatanyangleupto15°fromthevertical.

3 Protectionagainstrain.Waterfallinginrainatanangleequaltoorsmallerthan60°withrespecttotheverticalshallhavenoharmfuleffect.

4 Protectionagainstsplashing.Liquidsplashedfromanydirectionshallhavenoharmfuleffect.

5 Protectionagainstwaterjets.Waterprojectedbyanozzlefromanydirectionunderstatedconditionsshallhavenoharmfuleffect.

6Protectionagainstconditionsonships’decks(deckwithwatertightequipment).Waterfromheavyseasshallnotentertheenclosuresunderprescribedconditions.

7 Protectionagainstimmersioninwater.Itmustnotbepossibleforwatertoentertheenclosureunderstatedconditionsofpressureandtime.

8 Protectionagainstindefiniteimmersioninwaterunderspecifiedpressure.Itmustnotbepossibleforwatertoentertheenclosure.

X Indicatesnospecifiedprotection.

Onceagain,greatcaremustbetakentomaintaintheintegrityofthistypeofsystem,asaninadvertentconnection toearth,or interconnectionwithothercircuits,wouldrender theprotectionuseless.

AdditionalprotectionbyRCDsisausefulback-uptoothermethodsofshockprotection.

The use of enclosures is not limited to protection against shock from contact with liveparts;theyclearlyprovideprotectionagainsttheingressofforeignbodiesandmoisture.Inorder to establish to what degree an enclosure can resist such ingress, reference to theIndexofProtection(IP)code(BSEN60529)shouldbemade.Table0.1illustratespartoftheIPcode.

ThemostcommonlyquotedIPcodesinthe17theditionareIPXXBorIP2X,andIPXXDorIP4X.TheXdenotes that protection is not specified, not that there is noprotection. Forexample,anenclosure thatwas tobe immersed inwaterwouldbeclassified IPX8, therewouldbenopointusingthecodeIP68.

NoteIPXXBdenotesprotectionagainstfingercontactonly.IPXXDdenotesprotectionagainstpenetrationby1mmdiameterwifeonly.

CHAPTER1AnOverview

Importantterms/topicscoveredinthischapter:

StatutoryandNon-StatutoryRegulationsElectricalsystemsTheBuildingRegulationsPart‘P’Instruments

Bytheendofthischapterthereadershould:

be aware of the Statutory and Non-Statutory Regulations that are relevant toinstallationwork,

knowtherangeofinstrumentsrequired,knowtherequirementsregardingtheuseandperformanceoftestequipment.

So,hereyouareoutside thepremises,armedwith lotsof test instruments,aclipboard,apadofdocumentsthatrequirecompleting,theIETRegulations,GuidanceNotes3andaninstruction to carryoutan inspectionand testof theelectrical installation therein.Deadeasy,you’vebeentold,pieceofcake,justpokeaboutabit,‘Megger’thewiring,writetheresultsdown,signthetestcertificateandyoushouldbeontothenextjobwithinthehour!

Oh!Ifonlyitwerethatsimple!Whatiflethaldefectsweremissedbyjust‘pokingabout’?What if other tests should have been carried out which may have revealed seriousproblems?WhatifthingsgowrongafteryouhavesignedtosayallisinaccordancewiththeRegulations?Whatifyouwerenotactuallycompetenttocarryouttheinspectionandtest in the first place?What if … and so on, the list is endless. Inspection, testing andcertificationisaseriousand,inmanyinstances,acomplexmatter,soletuswindtheclockbacktothepointatwhichyouwereabouttoenterthepremisestocarryoutyourtests,andconsidertheimplicationsofcarryingoutaninspectionandtestofaninstallation.

What are the legal requirements in all of this?Wheredoyou stand if thingsgowrong?Whatdoyouneedtodotoensurecompliancewiththelaw?

ItisprobablybestatthispointtoconsiderthetypesofInspectionandTestthatneedtobeconductedandthecertificationrequired.

Therearetwotypes:

1.InitialVerification.2.PeriodicInspectionandTesting.

InitialVerificationisrequiredfornewworkandalterationsandadditions(coveredinCity&Guilds2392-10andthemoreadvanced2394-01).

Periodic Inspection and Testing is required for existing installations (this and InitialVerificationarecoveredinCity&Guilds2395-01).

The certification required for (1) (above) is an Electrical Installation Condition Report(EICR).

Thecertificationrequiredfor(2) (above) isaPeriodicInspectionReport(PIR).ThiscouldbereferredtoasaConditionReport.

Bothmustbeaccompaniedbyascheduleoftestresultsandascheduleofinspections.

In thecaseofanadditionor simplealteration thatdoesnot involve the installationofanew circuit (e.g. a spur from a ring final circuit), tests must be conducted but thecertificationrequiredisaMinorElectricalInstallationWorksCertificate(MEIWC).

TheseareallcoveredingreaterdetailinChapter16.

StatutoryandNon-StatutoryRegulations

Thestatutoryregulationsthatapplytoelectricalworkare:

TheHealthandSafetyatWorkEtc.Act(HSWA)TheElectricityatWorkRegulations(EAWR)TheBuildingRegulationsPart‘P’(applicabletodomesticinstallations).

Non-statutoryregulationsincludesuchdocumentsasBS7671:2008andassociatedguidancenotes,GuidanceNoteGS38ontestequipment,etc.

TheIETWiringRegulations(BS7671:2008)andassociatedguidancenotesarenotstatutorydocuments; they can, however, be used in a court of law to prove compliance withstatutory requirements such as the Electricity atWorkRegulations (EAWR) 1989,whichcover all work activity associated with electrical systems. A list of other statutoryregulationsisgiveninAppendix2oftheIETRegulations.However,itistheEAWRthataremostcloselyassociatedwithBS7671,andas such it isworthgivingsomeareasacloserlook.

IntheEAWRthereare33Regulationsinall,12ofwhichdealwiththespecialrequirementsofmines and quarries, onewhich dealswith extension outsideGreat Britain, and threewhich deal with effectively exemptions. We are only concerned with the first 16Regulations,andRegulation29,thedefenceregulation,whichweshallcomebacktolater.Letusstartthenwithacommentonthemeaningofelectricalsystemsandequipment.

ElectricalSystemsandEquipment

AccordingtotheEAWR,electricalsystemsandequipmentcanencompassanythingfrompowerstationstotorchorwrist-watchbatteries.Abatterymaynotcreateashockrisk,butmay cause burns or injury as a result of attempting to destroy it by fire, wherebyexplosions may occur. A system can actually include the source of energy, so a testinstrumentwithitsownsupply,forexample,acontinuitytester,isasysteminitself,andaloop impedance tester, which requires an external supply source, becomes part of thesystem intowhich it isconnected.Fromtheprecedingcomments itwillbeobvious thenthat, inbroad terms, if something is electrical, it isor ispartofanelectrical system.So,wheredoesresponsibilitylieforanyinvolvementwithsuchasystem?

The EAWR requires that every employer, employee and self-employed person beresponsible for compliance with the Regulations with regard to matters within theircontrol,andas suchareknownasdutyholders.Where thendoyou standas thepersonabouttoconductaninspectionandtestofaninstallation?Mostcertainly,youareadutyholder inthatyouhavecontrolof the installation insofarasyouwillultimatelypass theinstallationassafeormakerecommendationstoensureitssafety.Youalsohavecontrolofthetestinstrumentswhich,asalreadystated,aresystemsinthemselves,andcontroloftheinstallationwhilsttestingisbeingcarriedout.

AnybreachoftheRegulationsmayresultinprosecution,andunliketheotherlaws,undertheEAWRyouarepresumedguiltyandhavetoestablishyourinnocencebyinvokingtheDefence Regulation 29. Perhaps some explanation is needed here. Each of the 16Regulationshasastatus,inthatitiseitherabsoluteorreasonablypracticable.

Regulations that are absolute must be conformed to at all cost, whereas those that arereasonablypracticableareconformedtoprovidedthatallreasonablestepshavebeentakento ensure safety. For the contravention of an absolute requirement, Regulation 29 isavailable as a defence in the event of criminal prosecution, provided the accused candemonstratethattheytookallreasonableanddiligentstepstopreventdangerorinjury.

Noonewantstoendupincourtaccusedofnegligence,andsoweneedtobesurethatweknowwhatwearedoingwhenweareinspectingandtesting.

TheBuildingRegulationsPart‘P’

Part ‘P’ of the building regulation requires that installations in dwellings be designed,installed and inspected and tested to the requirements of the current edition of the IETWiringRegulations,BS7671.

Details of some suchwork need to be notified to the Local Authority Building Control(LABC).Thisisalegalrequirement.

Notifiablework

AnynewcircuitfedfromtheconsumerunitReplacementofaconsumerunitAnywork,additionsoralterationsinabath/showerroom,saunaorswimmingpool.

Non-notifiablework

Any other work that involves replacements, additions or alterations anywhere elseincludinggardens.

Certification

Allelectricalworkhastobeinspected,testedandcertifiedwiththeissueofeither:

AnElectrical InstallationCertificate (EIC) for all newcircuits and consumerunitreplacements

A Minor Electrical Installation Works Certificate (MEIWC) for small additionsand/oralterationsthatdonotcompriseanewcircuit

AnElectrical InstallationConditionReport (EICR)where the inspector isnot theinstaller.

Ifaninstallerbelongstoa‘CompetentPersons’scheme(i.e.isaDomesticInstallerwithanapprovalbody,say,theNICEIC,ELECSA,etc.),he/shecanself-certifytheworkandissuetheappropriatecertificatetothepersonorderingthework.TheapprovalbodywillnotifytheLABC.

Ifaninstallerisnotregisteredona‘CompetentPersons’scheme,butisqualifiedtoinspectand test, he/she should issue the appropriate certificate to theLABC.Theywill take theinspector’squalificationsintoaccountanddecideifanyfurtheractionneedstobetaken.

Aninstallerwhoisnotqualifiedtoinspectandtestmayappointa‘RegisteredCompetentPerson’tocarryouttheinspectionandtest.InthiscaseonlyanEICRcanbeissuedtothepersonorderingthework.

Apartfromtheknowledgerequiredcompetentlytocarryouttheverificationprocess,theperson conducting the inspection and test must be in possession of test instrumentsappropriatetothedutyrequiredofthem.

Instruments

Inordertofulfil thebasicrequirementsfortestingtoBS7671, thefollowinginstrumentsareneeded:

1.Alow-resistanceohmmeter(continuitytester).2.Aninsulationresistancetester.3.Aloopimpedancetester.4.Aresidualcurrentdevice(RCD)tester.5.Aprospectivefaultcurrent(PFC)tester.6.Anapprovedtestlamporvoltageindicator.7.Aprovingunit.8.Anearthelectroderesistancetester.

Manyinstrumentmanufacturershavedevelopeddualormulti-functioninstruments;henceitisquitecommontohavecontinuityandinsulationresistanceinoneunit,loopimpedanceand PFC in one unit, loop impedance, PFC and RCD tests in one unit, etc. However,regardless of the various combinations, let us take a closer look at the individual testinstrumentrequirements.

Low-resistanceohmmeters/continuitytesters

Bells, buzzers, simple multimeters, etc. will all indicate whether or not a circuit iscontinuous,butwillnotshowthedifferencebetweentheresistanceof,say,a10mlengthof 10mm2 conductor and a 10m length of 1mm2 conductor. I use this example as anillustration,asitisbasedonarealexperienceoftestingthecontinuityofa10mm2mainprotective bonding conductor between gas andwater services. The services, some 10mapart,wereateitherendsofadomesticpremises.The10mm2conductor,connectedtobothservices,disappearedunder the floor,andameasurementbetweenbothends indicatedaresistancehigherthanexpected.Furtherinvestigationrevealedthatjustunderthefloorateachend, the10mm2 conductorhadbeen terminated in a connector block and the joinbetween the two, about 8 m, had been wired with a 1 mm2 conductor. Only a milli-ohmmeterwouldhavedetectedsuchafault.

Alow-resistanceohmmetershouldhaveano-loadsourcevoltageofbetween4Vand24Va.c.ord.c.,andbecapableofdeliveringana.c.ord.c.short-circuitcurrentofnotlessthan200mA.Itshouldhavearesolution(i.e.adefeasibledifferenceinresistance)ofatleast0.01mV.

Insulationresistancetesters

Aninsulationresistancetestisthecorrecttermforthisformoftesting,notameggertest,asmeggerisamanufacturer’stradename,notthenameofthetest.

Aninsulationresistancetestermustbecapableofdelivering1mAwhentherequiredtestvoltageisappliedacrosstheminimumacceptablevalueofinsulationresistance.

Hence, an instrument selected for use on a low-voltage (50 V a.c.–1000 V a.c.) systemshouldbecapableofdelivering1mAat500Vacrossaresistanceof1MΩ.

Loopimpedancetester

Thisinstrumentfunctionsbycreating,ineffect,anearthfaultforabriefmoment,andisconnectedtothecircuitviaaplugorby‘flyingleads’connectedseparatelytoline,neutralandearth.

The instrument shouldonlyallowanearth fault toexist foramaximumof40ms,and a resolution of 0.01 V is adequate for circuits up to 50 A. Above this circuitrating, the ohmic values become too small to give such accuracy using a standardinstrument,andmorespecializedequipmentmayberequired.

RCDtester

Usuallyconnectedbytheuseofaplug,although‘flyingleads’areneededfornon-socketoutlet circuits, this instrumentallowsa rangeofout-of-balancecurrents to flow throughtheRCDtocauseitsoperationwithinspecifiedtimelimits.

Thelistinstrumentshouldnotbeoperatedforlongerthan2s,anditshouldhavea10percentaccuracyacrossthefullrangeoftestcurrents.

Earthelectroderesistancetester

Thisisa3-or4-terminal,battery-poweredresistancetester.ItsapplicationisdiscussedinChapter4.

PFCtester

ThisiseitherpartofacombinedPFC/Looptesteroramulti-functioninstrument.ItisusedtomeasureProspectiveShort-CircuitCurrent(PSCC)linetoneutral,orProspectiveEarthFaultCurrent(PEFC)linetoearth.

Approvedtestlamporvoltageindicator

Aflexiblecordwithalampattachedisnotanapproveddevice,norforthatmatteristheubiquitous‘testascope’or‘neonscrewdriver’,whichencouragesthepassageofcurrent,atlowvoltage,throughthebody!

AtypicalapprovedtestlampisshowninFigure1.1.

TheHealthandSafetyExecutive,GuidanceNoteGS38,recommendsthattheleadsandprobes,associatedwithtest, lamps,voltageindicators,voltmeters,etc.havethefollowingcharacteristics:

1. Theloadsshouldbeadequatelyinsulatedand,ideally,fused.2. Theleadsshouldbeeasilydistinguishedfromeachcitherfaycolour.3. Theleadsshouldbeflexibleandsufficientlylongfortheirpurpose,4. Theprobesshouldincorporatefingerbarriers,topreventaccidentalcontact

withliveparts.5. Theprobesshouldbe insulatedandhaveamaximumof2mmofexposed

metal,butpreferablyhavespring-loadedenclosedtips.

Provingunit

Thisisanoptionalitemoftestequipment,inthattestlampsshouldbeprovedonaknownlivesupplywhichcould,ofcourse,beanadjacentsocketorlightingpoint,etc.However,toproveatestlamponsuchaknownlivesupplymayinvolveentryintoenclosureswiththeassociated hazards that such entry could bring. A proving unit is a compact device notmuchlargerthanacigarettepacket,whichiscapableofelectronicallydeveloping230Vd.c.across which the test lamp may be proved. The exception to this are test lampsincorporating 230 V lamps which will not activate from the small power source of theprovingunit.

FIGURE1.1Approvedtestlamp.

Test lamps must to proved against a voltage similar to that to be tested. Hence,provingtestlampsthatincorporateaninternalcheck;thatis,shortingouttheprobestomakeabuzzersoundisriotacceptableifthevoltagetobefetedishigherthanthatdeliveredbythetestlamp.

Careoftestinstruments

TheEAWR(1989)requiresthatallelectricalsystems,andthisincludestestinstruments,bemaintained to prevent danger. This does not restrict such maintenance to just a yearlycalibration,butrequiresequipmenttobekeptingoodconditioninorderthatitissafetouse at all times. In consequence it is important to ensure the continual accuracy ofinstrumentsbycomparing test readingsagainstknownvalues.This ismostconvenientlyachievedbytheuseof‘checkboxes’whicharereadilyavailable.

Whilst test instruments and associated leads, probes and clips, etc. used in the electricalcontracting industry are robust in design andmanufacture, they still need treatingwithcareandprotectingfrommechanicaldamage.Keeptestgearinaseparateboxorcaseawayfromtoolsandsharpobjects,andalwayscheckthegeneralconditionofatesterandleadsbeforetheyareused.

Questions

1.Statethestatutorydocumentmostrelevanttoinspectionandtesting.2.Whatistheminimumshort-circuitcurrenttobedeliveredbyalowresistance

ohmmeter?3.Whatcurrentmustbedeliveredaninsulationresistancetesterwhenusedat

500Vacrossaresistanceof1MΩ?

4.StatethetwotestscarriedoutbyaRFCtester.5. What is the maximum length of exposed tip on the leads of a voltage

indicator?

Answers

1.ElectricityatWorkRegulations(1989).2.200mA.3.1mA.4.ProspectiveShort-CircuitCurrent(PSCC)andProspectiveEarthFaultCurrent

(PEFC).5.2mm.

CHAPTER2InitialVerification


InitialverificationdocumentationSequenceoftestsInspectionchecklist


knowthecorrectsequenceofteststobecarriedout,beawareoftheinformationrequiredbyaninspector,beawareoftheextentoftheinspectionsrequired.

CircumstancesWhichRequireanInitialVerification

Newinstallationsoradditionsoralterations.

GeneralReasonsforInitialVerification

1.Toensureequipmentandaccessoriesaretoarelevantstandard.2.ToprovecompliancewithBS7671.3.Toensurethattheinstallationisnotdamagedsoastoimpairsafety.

InformationRequired

Assessmentofgeneralcharacteristicssections311,312and313togetherwithinformationsuchasdrawings,charts,etc.,inaccordancewithRegulation514.9.1(seeBS7671:2008).

DocumentationRequiredandtoBeCompleted

Electrical Installation Certificate (EIC) signed or authenticated for the design andconstructionandthenfortheinspectionandtest(couldbethesameperson).AscheduleoftestresultsandascheduleofinspectionsmustaccompanyanEIC.

SequenceofTests

TheIETRegulationsindicateapreferredsequenceoftestsandstatethatif,duetoadefect,compliancecannotbeachieved,thedefectshouldberectifiedandthetestsequencestartedfrom the beginning. The tests for ‘Protection by separation’ and ‘Insulation of non-conductingfloorsandwalls’allrequirespecialistequipmentandinconsequencewillnotbediscussedhere.Thesequenceoftestsforaninitialinspectionandtestisasfollows:

1.Continuityofprotectiveconductors.2.Continuityofringfinalcircuitconductors.3.Insulationresistance.4.Protectionagainstdirectcontactbybarriersorenclosures.5.Polarity.6.Earthelectroderesistance.7.Earthfaultloopimpedance.8.Additionalprotection(RCDs).9.Prospectivefaultcurrentbetweenliveconductorsandtoearth.10.Phasesequence.11.Functionaltesting.12.Voltagedrop(notnormallyrequiredforinitialverification).

BS 7671:2008 requires tests 1-5 to be carried out in that order before the installation isenergized and, if there is an earth electrode, its testing should be included. It does notrequirethelivetests7-11tofollowasequenceanditem12isnotusuallyrequiredforaninitialverification.

Even though no sequence is specified, itwould always be appropriate to conduct test 7beforetest8ashighvaluesofloopimpedanceortheabsenceofanearthpathcouldresultin dangerous voltages appearing between exposed and extraneous conductive parts andpersonsshouldbetoldnottotouchmetalworkwhilstthetestisbeingconducted.

OneothertestnotincludedinPart6oftheIETRegulationsbutwhichneverthelesshastobecarriedoutisexternalearthfaultloopimpedance(Ze).

Beforeanytestingiscarriedout,adetailedphysicalinspectionmustbemadetoensurethatall equipment is to a relevant British or Harmonized European Standard, that it iserected/installedincompliancewiththeIETRegulations,andthatitisnotdamagedsuchthat it could cause danger. In order to complywith these requirements, the Regulationsgiveachecklistofitemsthat,whererelevant,shouldbeinspected.

However, before such an inspection, and test for that matter, is carried out, certaininformation must be available to the verifier. This information is the result of theassessmentoffundamentalprinciplesBS7671Section131andtheAssessmentofGeneral

Characteristics required by IETRegulations Part 3, sections 311, 312, 313, and drawings,charts and similar information relating to the installation. It is at this point that mostreaders who work in the real world of electrical installation will be lying on the floorlaughinghysterically.

Let us assume that the designer and installer of the installation are competentprofessionals,andalloftherequireddocumentationisavailable.

Interestingly,oneoftheitemsonthechecklististhepresenceofdiagrams,instructionsandsimilarinformation.IfthesearemissingthenthereisadeviationfromtheRegulations.

Anotheritemonthelististheverificationofconductorsforcurrent-carryingcapacityandvoltagedropinaccordancewiththedesign.Howonearthcanthisbeverifiedwithoutallthe information?A30ATypeBcircuitbreaker (CB)orType2miniaturecircuitbreaker(MCB)protectingalengthof4mm2conductormaylookreasonable,butisitcorrect,andareyoupreparedtosigntosaythatitisunlessyouaresure?Letuslookthenatsomeitemsthatwouldneedinspecting.

1.Connectionofconductors:Areterminationselectricallyandmechanicallysound?Is insulation and sheathing removed only to a minimum to allow satisfactorytermination?

2. Identification of conductors: Are conductors correctly identified in accordancewiththeRegulations?

3. Routing of cables: Are cables installed such that account is taken of externalinfluencessuchasmechanicaldamage,corrosion,heat,etc.?

4.Conductor selection: Are conductors selected for current-carrying capacity andvoltagedropinaccordancewiththedesign?

5. Connection of single pole devices: Are single pole protective and switchingdevicesconnectedinthelineconductoronly?

6.Accessoriesandequipment:Areallaccessoriesanditemsofequipmentcorrectlyconnected?

7.Thermaleffects:Are fire barriers presentwhere required and protection againstthermaleffectsprovided?

8. Protection against shock: What methods have been used to attain both basicprotectionandfaultprotection?

9.Mutual detrimental influence: Arewiring systems installed such that they canhave no harmful effect on non-electrical systems, or those systems of differentcurrentsorvoltagesaresegregatedwherenecessary?

10.Isolationandswitching:Arethereappropriatedevicesforisolationandswitchingcorrectlylocatedandinstalled?

11.Undervoltage:Whereundervoltagemaygiveriseforconcern,arethereprotectivedevicespresent?

12.Labelling: Are all protective devices, switches (where necessary) and terminals

correctlylabelled?13.Externalinfluences:Haveall itemsofequipmentandprotectivemeasuresbeen

selectedinaccordancewiththeappropriateexternalinfluences?14.Access:Areallmeansofaccesstoswitchgearandequipmentadequate?15.Noticesandsigns:Aredangernoticesandwarningsignspresent?16.Diagrams: Are diagrams, instructions and similar information relating to the

installationavailable?17. Erection methods: Have all wiring systems, accessories and equipment been

selectedandinstalledinaccordancewiththerequirementsoftheRegulations,andarefixingsforequipmentadequatefortheenvironment?

Alldefectsandomissions,etc.innewworkmustberectifiedand,inthecaseofanadditionsuchas,say,ashowercircuit,defectsfoundintheexistinginstallationthatareunrelatedtothenewworkshouldberecordedontheEIC.

Questions

1.Aninstallationistohavethefollowingtestsconducted:(1) loopimpedance,(2)polarity, (3) ringcircuitcontinuity,and (4) insulationresistance.What isthecorrectsequenceforcarryingoutthetests?

2.Whichtestisnotnormallyrequiredforaninitialverification?3.ThedetailsofwhichsectionsofBS7671arerequiredtobemadeavailabletoa

personcarryingputinspectionandtestingofaninstallation?4.Whatinspectionchecklistitemrelatestodamagetocables?

Answers

1.(3),(4),(2),(1).2.Voltagedrop.3.131,311,312,313.4.Routingofcables.

CHAPTER3TestingContinuityofProtectiveConductors

(Low-ResistanceOhmmeter)Importantterms/topicscoveredbythischapter:

ProtectivebondingconductorsCircuitprotectiveconductorsParallelearthpaths(R1+R2)values


knowwhattestinstrumenttouse,understandtheimportanceofdisconnectingprotectiveconductorsfortesting, know the importance of isolation, where protective conductors cannot be

disconnected,beawareoftheeffectsofparallelearthpaths, be able to determine the approximate value of a protective conductor, given its

length,knowthepreferredmethodofcpccontinuitytesting,knowwhy(R1+R2)valuesareimportant.

All protective conductors, including main protective and supplementary bondingconductors, must be tested for continuity using a low-resistance ohmmeter. A visualinspectionissufficientforshortlengthswheretheconductorsarevisiblethroughouttheirlength.

Formainprotectivebondingconductorsthereisnosinglefixedvalueofresistanceabovewhich the conductorwould be deemed unsuitable. Eachmeasured value, if indeed it ismeasurable for very short lengths, should be compared with the relevant value for aparticularconductorlengthandsize.SuchvaluesareshowninTable3.1.

Where a supplementary bonding conductor has been installed between simultaneouslyaccessibleexposedandextraneousconductivepartsasan

Table3.1Resistance(inΩ)ofCopperConductorsat20°C

additiontofaultprotectionandthere isdoubtas totheeffectivenessof theequipotentialbonding,thentheresistance(R)oftheconductormustbeequaltoorlessthan50/Ia.So,R≤50/Iawhere50isthevoltageabovewhichexposedmetalworkshouldnotrise,andIaistheminimumcurrentcausingoperationofthecircuitprotectivedevicewithin5s.

Forexample,supposea45ABS3036fuseprotectsacookercircuit,thedisconnectiontimeforthecircuitcannotbemet,andsoasupplementarybondingconductorhasbeeninstalledbetweenthecookercaseandanadjacentcentralheatingradiator.Theresistance(R)ofthatconductorshouldnotbegreaterthan50/Ia,andIainthiscaseis145A(seeFigure3.2BoftheIETRegulations);thatis,50/145=0.34Ω.

Howthendoweconductatesttoestablishcontinuityofmainorsupplementarybondingconductors?Quitesimplereally:justconnecttheleadsfromalow-resistanceohmmetertotheendsof thebondingconductor(Figure3.1).Oneendshouldbedisconnected fromitsbondingclamp,otherwiseanymeasurementmayincludetheresistanceofparallelpathsofotherearthedmetalwork.Remember tozero/null the instrument firstor, if this facility isnot available, record the resistance of the test leads so that this value can be subtractedfromthetestreading.

FIGURE3.1Testingmainprotectivebonding.

ImportantNoteIf the installation is in operation, then never disconnect protective bondingconductorsunlessthesupplycanbeisolated.Withoutisolation,personsandlivestock

areatriskofelectricshock.Inthisinstance,orwheretheconnectionstoextraneousconductive parts are not accessible, the test is conducted either between theconnected bonding conductors or between extraneous conductive parts. Theresistancevalueobtainedshouldbenogreaterthan0.05Ω.

Thecontinuityofcircuitprotectiveconductorsmaybeestablishedinthesameway,butasecondmethodispreferred,astheresultsofthissecondtestindicatethevalueof(R1+R2)forthecircuitinquestion.

Thetestisconductedinthefollowingmanner:

1.Temporarilylinktogetherthelineconductorandcpcofthecircuitconcernedinthedistributionboardorconsumerunit.

2. Test between line and cpc at each outlet in the circuit. A reading indicatescontinuity.

3.Recordthetestresultobtainedatthefurthestpointinthecircuit.Thisvalueis(R1+R2)forthecircuit,andisimportantforusewiththeformulaZs=Ze+(R1+R2)forconfirmingmeasuredvaluesofZsorforcalculationwhereZscannotbemeasured.Itshouldalsobenotedthatforlightingcircuitsthetestshouldbecarriedoutattheswitches,asthesearethefurthestpointforeachluminaire.

Figure3.2illustratestheabovemethod.

Theremaybesomedifficultyindeterminingthe(R1+R2)valuesofcircuitsininstallationsthatcomprisesteelconduitandtrunking,and/orsteel-wire-armoured(SWA)andmineral-insulatedmetal-sheathed(MIMS)cables,becauseoftheparallelearthpathsthatarelikelytoexist.Inthesecases,continuitytestsmayhavetobecarriedoutattheinstallationstagebeforeaccessoriesareconnectedorterminationsmadeoffaswellasaftercompletion.

Althoughitisnolongerconsideredgoodworkingpracticetousesteelconduitortrunkingas a protective conductor, it is permitted, and hence its continuitymust be proved. Theenclosure must be inspected along its length to ensure that it is sound and then thestandardlow-resistancetestisperformed.

FIGURE3.2Testingcpccontinuity.

Questions

1.Whatinstrumentisusedfortestingthecontinuityofprotectiveconductors?2. What would be the approximate resistance value of a 10 mm2 protective

bondingconductor,15mlong?3. What may be the effect on a resistant test reading taken between the

connectedendsofaprotectivebondingconductor?4.Where,onalightingcircuit,shouldacpccontinuitytestbeconducted?5.WhatisthesignificanceofthereadingattheendofthecircuitinQ.4above?6.Whyisavalueof(R1+R2)important,otherthanconfirmingcpccontinuity?

Answers

1.Low-resistanceohmmeter.2.0.03Ω.3.A lowervalueof resistance than the actual conductorvaluedue toparallel

earthpaths.4.Atallpointsonthecircuit.5.Itis(R1+R2forthecircuit.6.ItcanbeusedintheformulaZs=Ze+(R1+R2)toconfirmameasuredvalue

ofZsoftocalculateaZsvaluewheremeasurementisnot-possible.

CHAPTER4TestingContinuityofRingFinalCircuitConductors(Low-ResistanceOhmmeter)


Low-resistanceohmmeterRingfinalcircuitinterconnectionsSpurs(R1+R2)valuesInterpretationoftestvalues


knowthereasonsforconductingaringfinalcircuitcontinuitytest,understandtheproblemsthatinterconnectionsmaycreate,understandwhyinitialconductorcross-connectionsaremadeforthetest,knowhowincorrectinitialcross-connectionsarerevealed,knowwhyLtocpcvaluesforflat-sheathedcablesvaryslightlyduringthetest,beabletointerprettestresults.

Therearetwomainreasonsforconductingthistest:

1.Toensurethattheringcircuitconductorsarecontinuous,andindicatethevalueof(R1+R2)forthering.

2.Toestablishthatinterconnectionsintheringdonotexist.

Whatthenareinterconnectionsinaringcircuit,andwhyisitimportanttolocatethem?Figure4.1showsaringfinalcircuitwithaninterconnection.

Themost likelycauseofthesituationshowninFigure4.1 iswhereaDIYenthusiasthasaddedsocketsP,Q,RandStoexistingringsA,B,C,D,EandF.

FIGURE4.1RingCircuitwithaninterconnection.

FIGURE4.2Measurementacrossdiameterofacircle.

Initselfthereisnothingwrongwiththis.Theproblemarisesifabreakoccursat,say,pointY,ortheterminationsfailinsocketCorP.ThentherewouldbefoursocketsallfedfromthepointXwhichwouldthenbecomeaspur.

So, how do we identify such a situation with or without breaks at point Y? A simpleresistance test between the ends of the line, neutral or circuit protective conductorswillonlyindicatethatacircuitexists,whetherthereareinterconnectionsornot.Thefollowingtestmethodisbasedonthephilosophythattheresistancemeasuredacrossanydiameterofaperfectcircleofconductorwillalwaysbethesamevalue(Figure4.2).

Theperfectcircleofconductorisachievedbycross-connectingthelineandneutrallegsofthering(Figure4.3).Thetestprocedureisasfollows:

FIGURE4.3Measurementacrossdiameterofaringcircuit.

FIGURE4.4Ringcircuitcross-connectionsL—N.

1. Identifytheopposite legsof thering.This isquiteeasywithsheathedcables,but

with singles, each conductor will have to be identified, probably by takingresistancemeasurementsbetweeneachoneandtheclosestsocketoutlet.Thiswillgivethreehighreadingsandthreelowreadings,thusestablishingtheoppositelegs.

2.Takearesistancemeasurementbetweentheendsofeachconductorloop,r1,rnandr2.Recordthesevalues.

3.Cross-connecttheoppositeendsofthelineandneutralloops(Figure4.4).4.Measurebetweenlineandneutralateachsocketonthering.Thereadingsobtained

shouldbe,foraperfectring,substantiallythesame,andapproximatelyhalfofthereadingof individual loops. IfaninterconnectionexistedsuchasshowninFigure4.1, then sockets A—F would all have similar readings, and those beyond theinterconnectionwouldhavegraduallyincreasingvaluestoapproximatelythemidpoint of the ring, then decreasing values back towards the interconnection. If abreakhadoccurredatpointYthenthereadingsfromsocketSwouldincreasetoamaximumatsocketP.Oneortwohighreadingsarelikelytoindicateeitherlooseconnectionsorspurs.Anullreading,thatis,anopencircuitindication,isprobablyareversepolarity,eitherline-orneutral-cpcreversal.Thesefaultswouldclearlyberectified and the test at the suspect socket(s) is repeated. If the reading increasesdramatically to the centre of the ring and then decreases again, it is likely thatincorrectinitialcross-connectionsofthelegsoftheringhavebeenmadeatStep3.

5.Repeat theaboveprocedure,but in thiscasecross-connect the lineandcpc loops(Figure4.5).

Inthisinstance,ifthecableisoftheflattwintype,thereadingsateachsocketwillincreasevery slightlyand thendecreasearound the ring.Thisdifference,due to the lineandcpcbeingdifferent sizes,willnotbe significantenough tocauseanyconcern.Themeasuredvalueisveryimportant;itisR1+R2forthering.

Asbefore,looseconnections,spursand,inthiscase,L—Ncross-polaritywillbepickedup.

FIGURE4.5Ringcircuitcross-connectionsL—cpc.

ThedetailsinTable4.1aretypicalapproximateohmicvaluesforahealthy70mringfinalcircuitwired in 2.5mm2/1.5mm2 flat twin and cpc cable. (In this case the cpc will beapproximately1.673theLorNresistance.)

As already mentioned, null readings may indicate a reverse polarity. They could alsoindicatetwistedconductorsnot intheir terminalhousing.TheexamplesshowninFigure

4.6mayhelptoexplainthesesituations.

Table4.1ResistanceValuefora70mRingCircuit

L1-L2(r1) N1-N2(rn) cpc1-cpc2(r2)Initialmeasurements 0.52 0.52 0.86Readingateachsocket 0.26 0.26 0.32-0.34Forspurs,eachmetreinlengthwilladdthefollowingresistancetotheabovevalues

0.015 0.015 0.02

FIGURE4.6Reasonsfornullreadings.

Questions

1.Statethereasonsforconductingaringfinalcircuitcontinuitytest.2.WhatinstrumentistobeusedforthetestinQ1above?3.Whyareinterconnectionsinringcircuitsunacceptable?4.Whyaretheendsofcircuitconductorscross-connectedfortestpurposes?5.Whataretheeffectsontestresultsofcorrectandincorrectinitialconductor

cross-connections?6.Whatmayanullreadingatasocketoutletindicate?7.WhatdoestheL—cpcreadingateachsocketoutletonaringsignify?8.Whywill the L—cpc readings increase slightly and thendecrease around a

ringcircuitwiredinflatsheathedcable?9.Aringfinalcircuit iswiredin2.5mm2 singles (L,Nandcpc) inconduit. If

eachloophasanend-to-endvalueof0.4Ω,whatwouldbetheapproximateexpectedvalueof(R1+R2)?

Answers

1.Ensuringtheringiscontinuousandwithnointerconnections,andtoestablishavaluefor(R1+R2).

2.Alow-resistanceohmmeter.3.Abreakintheringbeyondaninterconnectionmayleavetwoormoresocket

outletsonaspur.4.Tocreateaperfectcircleofconductor,theresistanceacrossanydiameterof

whichwillgivethesamevalue.5. Correct cross-connections give the same reading at each socket outlet,

incorrectwill result ingreatly increasedanddecreased readingsaround thering.

6.Twistedortouchingconductorsnotinthesocketoutletterminalorareversepolarity.

7.(R1+R2)forthering.7.Becausethecpcissmallerinsizethanthelineconductor.8.0.2Ω.

CHAPTER5TestingInsulationResistance(Insulation

ResistanceTester)Importantterms/topicscoveredinthischapter:

InsulationresistancetesterParallelresistancesDisconnectionofequipmentTestprocedureTestvaluesSELV,PELVandFELVcircuitsSurgeprotectivedevices


beawareofwhythetestisrequired,knowthetestinstrumenttobeused,understandthatinsulationisameasureofresistancesinparallel,knowbetweenwhichconductorsthemeasurementsshouldbemade,knowthetestvoltagesandminimumvaluesofinsulationresistance,beawareoftheneedtotestoncircuits/equipmentthathavebeenisolated,beawareofthereasonsfordisconnectingvariousitemsofequipment, beable to calculateoverallvaluesof insulation resistancegiven individual circuit

values.

This isprobably themostusedandyetabused testof themall.Affectionatelyknownas‘meggering’,aninsulationresistancetestisperformedinordertoensurethattheinsulationof conductors, accessories and equipment is in a healthy condition, and will preventdangerousleakagecurrentsbetweenconductorsandbetweenconductorsandearth.Italsoindicateswhetheranyshort-circuitsexist.

Insulationresistance,asjustdiscussed,istheresistancemeasuredbetweenconductorsandismadeupofcountlessmillionsofresistancesinparallel(Figure5.1).

FIGURE5.1Parallelresistanceofcableinsulation.

The more resistances there are in parallel, the lower the overall resistance, and, inconsequence, the longer a cable, the lower the insulation resistance.Add to this the factthatalmostallinstallationcircuitsarealsowiredinparallel,anditbecomesapparentthattests on large installationsmay, ifmeasured as awhole, give pessimistically lowvalues,eveniftherearenofaults.

Underthesecircumstances, it isusualtobreakdownsuchlargeinstallationsintosmallersections, floorby floor,distributioncircuitbydistributioncircuit, etc.Thisalsohelps, inthecaseofperiodictesting,tominimizedisruption.Thetestprocedureisasfollows:

1.Ensurethesupplytothecircuit/sinquestionisisolated.2.Disconnectallitemsofequipmentsuchascapacitorsandindicatorlampsasthese

are likely togivemisleadingresults.Removeany itemsofequipment likely tobedamagedby the test, suchasdimmer switches, electronic timers, etc.Removealllampsandaccessoriesanddisconnectfluorescentanddischargefittings.Ensureallfusesareinplace,andcircuitbreakersandswitchesareintheonposition.Insomeinstances itmaybe impracticable to remove lamps,etc.and in thiscase the localswitchcontrollingsuchequipmentmaybeleftintheoffposition.Whereelectronicdevicescannotbedisconnected,testonlybetweenlivesandearth.

3.Jointogetherallliveconductorsofthesupplyandtestbetweenthisjoinandearth.Alternatively,testbetweeneachliveconductorandearthinturn.

4.Testbetweenlineandneutral.Forthreephasesystems,jointogetherall linesandtestbetweenthisjoinandneutral.

5. Then test between each of the lines.Alternatively, test between each of the liveconductorsinturn.Installationsincorporatingtwo-waylightingsystemsshouldbetested twice with the two-way switches in alternative positions. Note: all cpcsshouldbeconnectedtotheearthingarrangement(earthbar)duringthistest.

Table5.1givesthetestvoltagesandminimumvaluesofinsulationresistanceforELVandLVsystems.

If a value of less than 2 MΩ is recorded it may indicate a situation where a fault isdeveloping,butasyetstillcomplieswiththeminimumpermissiblevalue.Inthiscaseeachcircuitshouldbetestedseparatelyinordertolocatetheproblem.

InthecaseofSELV,PELVandelectricalseparation,Table5.1appliestotheirowncircuitconductors. When they are with other circuits the insulation resistance between theirconductorsandthoseoftheothercircuitsshouldbebasedonthehighestvoltagepresent.ForFELVcircuitsthetest

Table5.1InsulationResistanceTestRequirements

System TestVoltage MinimumInsulationResistanceSELVandPELV 250Vd.c. 0.5MQLVupto500V 500Vd.c. 1.0MQOver500V 1000Vd.c. 1.0MQ

voltageandtheminimumvalueifinsulationisthesameasthatforLVcircuitsupto500V(i.e.500Vd.c.and1MΩ).

Wheresurgeprotectivedevicesexist,theyshouldbedisconnected.Ifthisisnotpracticablethe test voltage may be reduced to 250 V d.c. but the minimum value of insulationresistanceremainsat1MΩ.

Example5.1

An installationcomprising sixcircuitshas individual insulation resistancesof2.5, 8, 200,200,200and200MΩ,andsothetotalinsulationresistancewillbe:

=0.4+0.125+0.005+0.005+0.005=0.545

Thisisclearlygreaterthanthe1.0MΩminimumbutlessthan2MΩ.Hadthisvalue(1.83)beenmeasuredfirst,thecircuitswouldneedtohavebeeninvestigatedtoidentifytheone/sthatweresuspect.

NoteIt is important that a test for cpc Continuity is conducted before an insulationresistance (IR) test. If a cpcwas broken, and an IR test between line and cpcwascarried out first, the resultwould be satisfactory, even if therewas an L-cpc faultbeyond the break.A subsequent cpc continuity testwould reveal the break,whichwouldberectified,leavinganL-cpcfaultundetected!!

Questions

1.Whatisthepurposeofaninsulationresistancetest?2.Whatinstrumentshouldbeused?3.Whydocapacitors,neons,etc.needtobedisconnected?4.Whydoitemsofelectronicequipmentneedtobedisconnected?5.Whatactionshouldbetakenregardingswitchesandprotectivedevices?6.Whatisthetestvoltageandminimumvalueofinsulationresistancefora25

VFELVcircuit?7.Whattestvoltageandminimumvalueofinsulationresistanceareappropriate

forcircuitsincorporatingsurgeprotectivedevices?8.Belowwhatvalueofoverallinsulationresistancewouldaninstallationneed

tobeinvestigatedcircuitbycircuit?9. Why may a large installation give a pessimistically low overall insulation

resistancevalue?

10.Whatwouldbethetotal insulationresistanceofaninstallationcomprisingcircuitswiththefollowingvalues:3MΩ,12MΩ,100MΩand150MΩ?

Answers

1.Toensurethatconductorinsulationhasnotdeterioratedorbeendamagedtoanextentthatexcessiveleakagecurrentscanflow.

2.Aninsulationresistancetester.3.Toavoidmisleadingtestresults4.Toavoiddamagetosuchequipment.5.AllswitchesON,allfusesIN,allcircuitbreakersON.6.500Vd.c.;lMΩ.7.250Vd.c.;lMΩ.8.2MΩ.9.Becausetherearealargenumberofcircuitsallinparallel.10.2.3MΩ.

CHAPTER6SpecialTests

Thenext two tests are special in that they arenot often required in the general type ofinstallation.Theyalsorequirespecialtestequipment.Inconsequence,therequirementsforthesetestswillonlybebrieflyoutlinedinthisshortchapter.

ProtectionbyBarriersorEnclosures

If,onsite,basicprotectionisprovidedbyfabricatinganenclosureorerectingabarrier,itmustbeshownthattheenclosurecanprovideadegreeofprotectionofatleastIPXXBorIP2Xor,whererequired,atleastIPXXDorIP4X.

AnenclosurehavingadegreeofprotectionIP2Xcanwithstandtheingressofsolidobjectsexceeding 12mmdiameter and fingers, IPXXB is protection against finger contact only.IP4Xgivesprotectionagainstsolidobjectsandwiresexceeding1mmindiameter,IPXXDprotectsagainstwiresexceeding1mmindiameteronly.

ThetestforIPXXBorIP2Xisconductedwitha‘standardtestfinger’whichissuppliedatatestvoltagenot less than40Vd.c.andnotmore than50Vd.c.Oneendof the finger isconnectedinserieswithalampandlivepartsintheenclosure.Whentheendofthefingeris introduced into the enclosure, provided the lampdoesnot light then the protection issatisfactory(Figure6.1).

ThetestforIPXXDorIP4Xisconductedwitharigid1mmdiameterwirewithitsendcutatrightangles.Protectionisaffordedifthewiredoesnotentertheenclosure.

ProtectionbyNon-ConductingLocation

This is a rare location and demands specialist equipment to measure the insulationresistance between insulated floors andwalls at various points.Appendix 13 ofBS 7671outlinesthetestsrequired.

FIGURE6.1BSfingertest.

CHAPTER7TestingPolarity(Low-ResistanceOhmmeter)


EdisonscrewlampholdersRadialsocketoutletcircuitsSupplypolarity


knowtheinstrumenttobeused,knowwhyBSEN60238,E14andE27lampholdersareexemptfrompolaritytesting, know why ring final circuit polarity is not usually carried out during polarity

testing,knowhowtocheckforline—cpcreversalsonradialsocketoutletcircuits,knowwhatlivepolaritytestshouldbeconducted.

Thissimpletest,oftenoverlooked,isjustasimportantasalltheothers,andmanyseriousinjuries and electrocutions could have been prevented if only polarity checks had beencarriedout.

Therequirementsare:

1.Allfusesandsinglepoleswitchesandprotectivedevicesareinthelineconductor.2. The centre contact of an Edison screw type lampholder is connected to the line

conductor (except E14 and 27 types to BS EN 60238, as these have threads ofinsulatingmaterialandthelampmustbefullyinsertedbeforeLandNcontactsaremade).

3.Allsocketoutletsandsimilaraccessoriesarecorrectlywired.

Although polarity is towards the end of the recommended test sequence, itwould seemsensible,onlightingcircuits,forexample,toconductthistestatthesametimeasthatforcontinuityofcpcs(Figure7.1).

As discussed earlier, polarity on ring final circuit conductors is achieved simply byconducting the ring circuit test. For radial socket outlet circuits, however, this is a littlemoredifficult.Thecontinuityofthecpcwillhavealreadybeenprovedbylinkinglineandcpcandmeasuringbetweenthesameterminalsateachsocket.Whilstaline—cpcreversalwould not have shown, a line—neutral reversal would, as there would have been noreadingat thesocket inquestion.Thiswouldhavebeenremedied,andsoonly line—cpcreversalsneedtobechecked.Thiscanbedonebylinkingtogethercpcandneutralatthe

origin and testing between the same terminals at each socket. A line—cpc reversal willresultinnoreadingatthesocketinquestion.

Forlightingcircuits,thetestisthesameastheR1+R2test,sopolarityischeckedthen.Thesameappliestotheradialsocketoutletcircuitsifthesocketfrontsareopentotestattheactualcableterminations,asline—cpcreversalswillbevisible.

Livepolarity

Whenthesupplyisconnected,itisimportanttocheckthattheincomingsupplyiscorrect.Thisisdoneusinganapprovedvoltageindicatorattheintakepositionorclosetoit.

FIGURE7.1Lightingcircuitpolarity.

Questions

1.Whatinstrumentisusedfortestingpolarity?2.WhyareBSEN60238E14andE27lampholdersexemptfrompolaritytesting?3.Atwhatpointinatestsequenceisthepolarityofaringfinalcircuitchecked?4.Howareline—cpcreversalsidentifiedinradialsocketoutletcircuits?5.Whereshouldlivepolaritytestsbeconducted?

Answers

1.Low-resistanceohmmeter.2.Thelampholderscrewthreadismadeofaninsulatingmaterial.3.WhentheringfinalcircuitcontinuityKitisbeingconducted.4.Bycross-connectingneutralandcpcandtestingbetweenNandcpcateach

socket.5.Atthesupplyintaketotheinstallation.

CHAPTER8TestingEarthElectrodeResistance(Earth

ElectrodeResistanceTesterorLoopImpedanceTesters)


EarthelectroderesistanceareaPotentialdividerCurrentandpotentialelectrodesAveragevalueofearthelectroderesistanceUseofearthfaultloopimpedancetester


knowthetestinstrumentsthatmaybeused,understandwhatismeantbytheresistanceareaofanearthelectrode, be able to state the electrodes involvedwhen using an earth electrode resistance

tester,knowtheextentoftheresistanceareaofanelectrode,knowhowtoconductatestusinganearthelectroderesistancetester,knowwhattestmaybeconductedwhenthesystemisTTandisRCDprotected,beabletodeterminethevalueofearthelectroderesistancefromtestresults.

Inmanyruralareas, thesupplysystemisTTandhencerelianceisplacedonthegeneralmassofearthforareturnpathunderearthfaultconditions.Connectiontoearthismadebyanelectrode,usuallyoftherodtype,andpreferablyinstalledasshowninFigure8.1.

Inordertodeterminetheresistanceoftheearthreturnpath,itisnecessarytomeasuretheresistance that the electrode haswith earth. If wewere tomake suchmeasurements atincreasinglylongerdistancesfromtheelectrode,wewouldnoticeanincreaseinresistanceofuptoabout2.5-3mfromtherod,afterwhichnofurtherincreaseinresistancewouldbenoticed(Figure8.2).

FIGURE8.1Earthelectrodeinstallation.

Themaximumresistancerecordedistheelectroderesistanceandtheareathatextendsto2.5-3mbeyondtheelectrodeisknownastheearthelectroderesistancearea.

There are twomethodsofmaking themeasurement, oneusingaproprietary instrumentandtheotherusingaloopimpedancetester.

Method1:ProtectionbyOvercurrentDevice

Thismethodisbasedontheprincipleofthepotentialdivider(Figure8.3).

ByvaryingthepositionoftheslidertheresistanceatanypointmaybecalculatedfromR=V/I.

The earth electrode resistance test is conducted in a similar fashion with the earthreplacingtheresistanceandapotentialelectrodereplacingtheslider(Figure8.4).InFigure8.4,theearthingconductortotheelectrodeundertestistemporarilydisconnected.

FIGURE8.2Earthelectroderesistancearea.

FIGURE8.3Potentialdivider.

FIGURE8.4Earthelectroderesistancetest.

Themethodoftestisasfollows:

1.Placethecurrentelectrode(C2)awayfromtheelectrodeundertest,approximately10timesitslength(i.e.30mfora3mrod).

2.Placethepotentialelectrodemidway.3.Connecttestinstrumentasshown.4.Recordresistancevalue.5.Movethepotentialelectrodeapproximately6meithersideofthemidposition,and

recordthesetworeadings.6.Takeanaverageofthesethreereadings(thisistheearthelectroderesistance).

For TT systems the result of this test will indicate compliance if the product of theelectroderesistanceandtheoperatingcurrentoftheovercurrentdevicedoesnotexceed50V.Clearlythiswillnotbeachievedwhenelectroderesistancesarehighandhencewillbemoreappropriateforelectrodesusedforearthconnectionsfortransformersandgeneratorswherethevaluesneedtobeverysmall.GenerallyspeakingthevaluesobtainedwillresultintheneedforRCDprotection.

Method2:ProtectionbyaResidualCurrentDevice

In this case, anearth fault loop impedance test is carriedoutbetween the incoming lineterminalandtheelectrode(astandardtestforZe).

ThevalueobtainedisaddedtothecpcresistanceoftheprotectedcircuitsandthisvalueismultipliedbytheoperatingcurrentoftheRCD.Theresultingvalueshouldnotexceed50V.If it does, then Method 1 should be used to check the actual value of the electroderesistance.

Questions

1.Whatinstrumentsmaybeusedforearthelectroderesistancetesting?2.Whatistheextentoftheresistanceareaofanearthelectrode?3. For a 4 m electrode under test, at what distance away should the current

electrodebeplaced?4.Where should a potential electrode be initially placedwhen conducting an

earthelectroderesistancetest?5.Wherearethealternativepositionsforthepotentialelectrode?6.Whatwould be the resistance of an earth electrode if the test results gave

valuesof127Ω,129Ωand122Ω?7.What test may be performedwhen the system is TT and protected by an

RCD?

Answers

1.Earthelectroderesistancetesterorearthfaultloopimpedancetester.2.Approximately2.5mradiusfromtheelectrode.3.40mminimum.4.Centrallybetweentheelectrodeundertestandthecurrentelectrode.5.6meithersideofthepotentialelectrode’sinitialposition.6.126Ω.7.Anearthfaultloopimpedancetest.

CHAPTER9TestingEarthFaultLoopImpedanceTester


EarthfaultlooppathComparisonofresultswithmaximumvaluesTheruleofthumbRCDandcboperationCalculationofloopimpedanceExternalearthfaultloopimpedance


knowwhatinstrumentisrequired,beconversantwiththevariousearthfaultlooppaths,knowthetestprocedure,knowhowtoadjustmaximumvaluesforcomparisonwithtestvalues,knowtoovercometheproblemsofRCDorcboperationduringthetest,beawareoftherequirementsfortestingexternalearthfaultloopimpedance.

This is very important but, sadly, poorly understood. So let us remind ourselves of thecomponentpartsoftheearthfaultlooppath(Figure9.1).Startingatthepointoffault:

1.Thecpc.2.Theearthingconductorandmainearthingterminal.3.Thereturnpathvia theearthforTTsystems,andthemetallicreturnpath in the

caseofTN-SorTN-C-Ssystems. Inthe lattercasethemetallicreturn is thePENconductor.

4.Theearthedneutralofthesupplytransformer.5.Thetransformerwinding.6.Thelineconductorbacktothepointoffault.

FIGURE9.1Earthfaultlooppath.

Overcurrentprotectivedevicesmust,underearthfaultconditions,disconnectfastenoughtoreduce theriskofelectricshock.This isachieved if theactualvalueof theearthfaultloopimpedancedoesnotexceedthetabulatedmaximumvaluesgivenintherelevantpartsoftheIETRegulations.

Thepurposeofthetest,therefore,istodeterminetheactualvalueoftheloopimpedance(Zs),forcomparisonwiththosemaximumvalues,anditisconductedasfollows:

1.Ensurethatallmainequipotentialbondingisinplace.2.ConnectthetestinstrumenteitherbyitsBS1363plug,orthe‘flyingleads’,tothe

line,neutral andearth terminalsat the remoteendof the circuitunder test. (If aneutralisnotavailable,e.g.inthecaseofathree-phasemotor,connecttheneutralprobetoearth.)

3.Presstotestandrecordthevalueindicated.

Itmustbeunderstoodthatthisinstrumentreadingisnotvalidfordirectcomparisonwiththetabulatedmaximumvalues,asaccountmustbetakenoftheambienttemperatureatthetimeoftestandthemaximumconductoroperatingtemperature,bothofwhichwillhaveaneffectonconductorresistance.Hence,the(R1+R2)couldbegreateratthetimeoffaultthanatthetimeoftest.

So, ourmeasured value ofZsmust be corrected to allow for these possible increases intemperature occurring at a later date. This requires actually measuring the ambienttemperatureandapplyingfactorsinaformula.

ClearlythismethodofcorrectingZsistimeconsumingandunlikelytobecommonlyused.Hence,aruleofthumbmethodmaybeappliedwhichsimplyrequiresthatthemeasuredvalue ofZs does not exceed 0.8 of the appropriate tabulatedmaximum value. Table 9.1gives the 0.8 values of tabulated loop impedance for direct comparison with measured

values.

Ineffect,aloopimpedancetestplacesaline/earthfaultontheinstallation,andifanRCDispresentitmaynotbepossibletoconductthetestasitwillkeeptrippingout.Unlesstheinstrument can compensate for this, thevalueofZswill have tobe calculatedusing themeasuredvaluesofZeand(R1+R2)andthe0.8ruleapplied.Remember,Zs=Ze+(R1+R2).

ExternalLoopImpedanceZe

ThevalueofZe ismeasuredat theoriginof the installationon the supply sidewith themeans of earthing disconnected, to avoid parallel paths. Do not conduct this test if theinstallationcannotbeisolated.

ImportantNoteNeverbypassanRCDinorder toconduct this test.Also,as this testcreatesahighcurrent,somelowerratedcbsmayoperateonoverload.Donotreplacewithahigherratedbreakerfortestpurposes;usethecalculationmethod.

Table3.5CorrectedMaximumZsValuesforComparisonwithMeasuredValues

Questions

1.Whatinstrumentisusedforearthfaultloopimpedancetesting?2.WhichearthingsystemincludesaPENconductor?3.Beforetesting,whatactionshouldbetakenregardingequipotentialbonding?4.Whyisthe0.8ruleapplied?5. Isameasuredvalueof loopimpedanceof1.2Ωsatisfactoryif thetabulated

maximumvalueis1.44Ω?6. How may a value for loop impedance Zs be obtained if an RCD or a cb

operateswhenthetestisconducted?7.What action is required regarding the earthing conductor of an installation

beforeconductingatestforexternalloopimpedanceZe?8.Why is the action inQ7 above required andwhat othermeasuremust be

taken?

Answers

1.Anearthfaultloopimpedancetester.2.TN-C-S.3.Ensureitisconnected.4.Tocompensateforincreasedambientandconductoroperatingtemperature.5.No,asthecorrectedmaximumwouldbe0.8×1.44=1.15Ω.6.CalculationfromZs=Ze+(R1+R2).7.Itmustbedisconnected.8.Toavoidparallelpaths.Thesupplytotheinstallationmustbeisolated.

CHAPTER10AdditionalProtection(RCDTester)

Importantterms/topicscoveredbythischapter:

RCD/RCBOtestrequirementsUsesforRCDs/RCBOsDeterminationofRCD/RCBOrating


knowwhatinstrumentshouldbeused,knowthetestrequirementsforvarioustypesofRCD/RCBO,knowtheinstrumentsettingsrequired,beabletoidentifywhereRCDs/RCBOsarerequired,knowhowtodeterminetheratingofRCDs/RCBOs.

RCD/RCBOOperation

WhereRCDsandRCBOsareusedasadditionalprotectionagainstshock,itisessentialthattheyoperatewithinsetparameters.TheRCDtestersusedaredesignedtodojustthis,andthebasictestsrequiredareasfollows(Table10.1):

Note

AloopimpedancetestmustbeconductedbeforetheRCDtestashighvaluesofloopimpedanceortheabsenceofanearthpathcouldresultindangerousvoltages appearing between exposed and extraneous conductive parts andpersons should be told not to touch metalwork whilst the test is beingconducted.MostRCDtestershave the facility to test, separately, eachhalf cycleof thesupply and so each test should bedone at 0° and 180°.Thehighest readingshouldberecorded.

1.SetthetestinstrumenttotheratingoftheRCD.2.Setthetestinstrumenttohalf-ratedtrip(1/2IΔn).3.OperatetheinstrumentandtheRCDshouldnottrip.4.Settheinstrumenttodeliverthefull-ratedtrippingcurrentoftheRCD(IΔn).5.OperatetheinstrumentandtheRCDshouldtripoutintherequiredtime.6.A30mARCDorless,operatingat5×IΔn,shouldtripin40ms.

Table10.1RCD/RCBOTestRequirements

RCDType Half-Rated Full-RatedTripCurrentBS4239andBS7288sockets Notrip <200ms

BS4239withtimedelay Notrip 1/2timedelay+200mstotimedelay+200ms

BSEN61009orBSEN61009RCBO Notrip <300msAsabovebutTypeSwithtimedelay Notrip 130ms≤l≤500ms

NoteThislasttestisnotrequiredforRCDsratedover30mA.

ThereseemstobeapopularmisconceptionregardingtheratingsandusesofRCDsinthattheyarethepanaceaforallelectricalillsandtheonlyusefulratingis30mA!

First, RCDs are not fail-safe devices; they are electromechanical in operation and can

malfunction.Second,generalpurposeRCDsaremanufacturedinratingsfrom5to500mAandhavemanyuses.Theacceptedlethallevelofshockcurrentis50mAandhenceRCDsratedat30mAorlesswouldbeappropriateforusewhereshockisanincreasedrisk.ThefollowinglistindicatestheresidualcurrentratingsandusesofRCDsasstatedinBS7671.

RequirementsforRCDProtection

30mA

Allsocketoutletsratedatnotmorethan20Aandforunsupervisedgeneraluse.Mobileequipmentratedatnotmorethan32Aforuseoutdoors.Allcircuitsinabath/showerroom.PreferredforallcircuitsinaTTsystem. All cables installed less than 50 mm from the surface of a wall or partition in

prescribedzonesandnotprotectedbyanyothermethod,andalsoatanydepthiftheconstructionofthewallorpartitionincludesmetallicparts.

Inzones0,1and2ofswimmingpoollocations.Allcircuitsinalocationcontainingsaunas,etc.Socketoutletfinalcircuitsnotexceeding32Ainagriculturallocations.CircuitssupplyingClassIIequipmentinrestrictiveconductivelocations.Eachsocketoutletincaravanparksandmarinasandfinalcircuitforhouseboats.Allsocketoutletcircuitsratednotmorethan32Aforshowstands,etc. All socket outlet circuits rated notmore than 32A for construction sites (where

reducedlowvoltage,etc.isnotused).Allsocketoutletssupplyingequipmentoutsidemobileortransportableunits.Allcircuitsincaravans.Allcircuitsincircuses,etc.AcircuitsupplyingClassIIheatingequipmentforfloorandceilingheatingsystems.

100mA

Socketoutletfinalcircuitsofratingexceeding32Ainagriculturallocations.

300mA

Attheoriginofatemporarysupplytocircuses,etc.Wherethereisariskoffireduetostorageofcombustiblematerials.Allcircuits(exceptsocketoutlets)inagriculturallocations.

500mA

Any circuit supplying one ormore socket outlets of rating exceeding 32A, on a

constructionsite.

Where loop impedance values cannot be met, RCDs of an appropriate rating can beinstalled.Theirratingcanbedeterminedfrom

whereIΔnistheratedoperatingcurrentofthedevice,50isthetouchvoltage,andZsisthemeasuredloopimpedance.

Questions

1.WhattestinstrumentisrequiredforRCD/RCBOtesting?2.What is themaximumoperating time foraBSEN61008RCDat full rated

current?3.What is themaximumoperatingtimefora30mARCDwhentestedat150

mA?4.WhatmaximumratingofRCDshouldbeusedfora63Asocketoutletona

constructionsite?5.WhatratingofRCDisrequiredforacaravaninstallation?6.Whatwould be the requiredmaximum rating of an RCDwhere the earth

faultloopimpedancewas167Ω?

Answers

1.AnRCDtester.2.300ms.3.40ms.4.500mA.5.30mA.6.300mA.

CHAPTER11ProspectiveFaultCurrent(PFC/PSCCTester)

There is a requirement to determine the prospective fault current at the origin of aninstallation and at relevant points throughout.At the origin thismay be ascertained byenquiryormeasurement,whereasatotherpointsmeasurementistheonlyoption.

WherethelowestratedprotectivedeviceintheinstallationhasabreakingcapacityhigherthanthePFCattheorigin,thenmeasurementatotherpointsisnotneeded.

The purpose of this test is to verify that the breaking capacity of a protective device issuitablefortheprospectivefaultcurrentatthepointthatitisinstalled.

Aprotectivedevicewithabreakingcapacityof,say,3kAinstalledinadistributionboardwherethePFCis6kAcouldresultinseriousdamageand/orfireintheeventofafault.

BSEN60898circuitbreakershave twovaluesofbreakingcapacity, theservicerating IcsandthefaultratingIcn.TheIcnratingismarkedonthedevice,e.g. ;atthisvalueoffaultcurrentthebreakerwilloperatebutmaynotbeusableafterwards.

PFCisagenerictermandcanbeeitherprospectiveshort-circuitcurrent,PSCC(betweenlinesorlineandneutral)orprospectiveearthfaultcurrent,PEFC(betweenlineandearth).Both should bemeasured and the highest value recorded, although there is no harm inrecordingboth.

Thetestersaredesignedforsingle-phaseuse,sowhereavalueofPSCCisrequiredforathree-phase system itmaybedeterminedbymultiplying the single phase by 2, ormoreaccurately1.732.

CHAPTER12CheckofPhaseSequence(PhaseSequence

Indicator)For three-phase systems it is important to have knowledge of the phase rotation of thesupplyandatvariouspointswithinaninstallation.ItisconventionforthisrotationtobenormallyBrown,Black,Grey, or L1, L2, L3. The direction of three-phasemotors can bereversed simply by reversing any two phases. In consequence the correct sequence isessentialtoensuretherightrotation.

Parallelingoftwothree-phasegeneratorsorofageneratortothethree-phasepublicsupplysystemrequirestheirphasesequencestobesynchronized.

The instrument is simply a small three-phasemotorwith a dial that indicates inwhichdirectionthesupplyisrotating(Figure12.1).

FIGURE12.1Phasesequenceindicator.

CHAPTER13FunctionalTesting

AllRCDshaveabuilt-intestfacilityintheformofatestbutton.Operatingthistestfacilitycreatesanartificialout-of-balanceconditionthatcausesthedevicetotrip.Thisonlychecksthemechanicsof the trippingoperation; it doesnot check the conditionof the electricalinstallationandhenceisnotasubstituteforthetestsdiscussedinChapter10.

Thereshouldbeanotice inaprominentpositionatornear theoriginof the installationwherethedeviceislocatedindicatingthatthetestbuttonshouldbeoperatedquarterly.Fortemporary installations it is recommended that this operation be carried out at moreregularintervals.

All other items of equipment such as switchgear, controlgear interlocks, etc. must bechecked to ensure that they are correctlymounted and adjusted, and that they functioncorrectly.

This could involve the operation of, for example, two-way switching, dimmer switches,timers,thermostats,mainisolators,circuitbreakers,etc.

CHAPTER14VoltageDrop(ApprovedVoltmeter)

Theremay be a requirement to determine the voltage at the terminals of equipment toensure that items of electrical equipment will function correctly and safely. As themaximum volt drop will occur when the circuit is at full load and at maximum cableoperating temperature it would be unlikely that an accurate instrument measurementwouldbeachievable.Hencethecalculationmethodisused.

ThisissimplybasedongoodoldOhm’slaw:V=I×R.

Allweneedisthelengthandcsaofthecable/conductorsorameasuredvalueofresistanceandthefullloadcurrent.

Example14.1

Amotorwithafullloadcurrentof10Aisfedfroma230Vsupplybya70°Cthermoplasticcableof total resistance (L+N)0.222Ωmeasuredat20°C.What is theexpectedvoltagedropandisitacceptable?

VoltdropV=I×R=10×0.222×1.2=2.66V(the1.2factorconvertsthe20°Cresistancetowhatitwouldbeat70°C).Thisisacceptable,asthemaximumis11.5V.

Alternativelywe could use the length, the csa and the tabulated resistance inmΩ/m at20°C.

In theexampleabove the lengthwouldhavebeen15mandthesingleconductorcsa2.5mm2whichhasaresistanceof7.41mΩat20°C.

Table14.1MaximumPermissibleVoltageDrop

LVLighting3% LVPower5%Single-phase230V 6.9V 11.5VThree-phase400V 12V 20V

CHAPTER15PeriodicInspection


CircumstancesrequiringperiodicinspectionandtestingGeneralreasonsforperiodicinspectionandtestingConditionstobeinvestigatedDocumentationtobecompletedGeneralareasofnon-compliancethatmayberevealed


knowwhyperiodicinspectionandtestingisrequired,knowwhatgeneralconditionswithinaninstallationneedinvestigation,knowwhatdocumentationneedstobecompleted,knowwhatactionisrequiredifthereisinsufficientinformation/drawings,etc.,understandtheextenttowhichdismantlingandsamplingshouldtakeplace, be aware of the conditions that may permit an installation to be exempt from

periodicinspectionandtesting.

PeriodicInspectionandTesting

This is the province of the experienced inspectorwho has not only the knowledge andtechnical expertise to competently carry out the testing process but who is also fullyconversantwithcorrectelectricalinstallationpractices.

The purpose of the periodic inspection and testing is to establish whether or not theinstallation is in a satisfactory condition for continued use. This is achieved by relevantinspectionandappropriatetesting.Themostimportanttestistheloopimpedancetest,asthiswillestablishifdisconnectiontimesarebeingmet.

Therearemanyinstanceswheretestingisnotrequired.Forexample,themainpurposeofconductingaringcircuitcontinuitytestistoestablishifthereareinterconnectionsinthering.Thus,iftherearerecordsofthetestresultsfrompreviousinspectionsandtherehasbeen nowork carried out on the circuit, then it is impossible for an interconnection tohappenonitsown!Hencetheringcircuittestisawasteoftime.

Infact,evenR1+R2testscanbeavoidedastheZstestswillshowthecontinuityofcpcs.Theonlyothertestwhichshouldbecarriedoutisinsulationresistance,astheremayhavebeensomedeteriorationsincethelastinspection.

Clearly,iftherearenoprevioustestresults,morecomprehensivetestingwillberequired.

In any case the inspector should conduct a walk round to establish the extent of anysamplingofthecircuitstobeinspected.Thissamplingmaybereducedorincreasedastheinspectionproceeds,dependingonthefindings.

It should also be noted that in its true sense, Periodic Inspection and Testing does notincludefaultfindingasthisistimeconsumingandfinanciallyprohibitive.Remember,thepurposeistoreportontheconditionoftheinstallation,nottorectifyit.

CircumstancesWhichRequireaPeriodicInspectionandTest

Testandinspectionisdue;insurance,mortgage,licensingreasons;changeofuse;changeofownership; after additions or alterations; after damage; change of loading; to assesscompliancewithcurrentregulations.

GeneralReasonsforaPeriodicInspectionandTest

1.Toensurethesafetyofpersonsandlivestock.2.Toensureprotectionofpropertyfromfireandheat.3.Toensurethattheinstallationisnotdamagedsoastoimpairsafety.4. To ensure that the installation is not defective and complies with the current

regulations.

GeneralAreasofInvestigation

Safety,Ageing,Damage,Corrosion,Overloading,Wearand tear,External influencesandSuitability(asanaidememoiretheauthorcallsthishisSADCOWESlist!).

DocumentationtoBeCompleted

Anelectricalinstallationconditionreport(EICR),ascheduleoftestresultsandascheduleofinspections.

SequenceofTests

Thereisnorequiredsequence.However,thesequenceforanInitialVerificationispreferredifpossible.

Periodic inspection and testing could be such a simple and straightforward process.Nevertheless,itusuallytendstobecomplicatedandfrustrating.

On the domestic scene, I doubt if any house owner actually decides to have a regularinspection,thecommentbeing,‘IfitworksitmustbeOK’.Itisusuallyonlywhenthereisa change of ownership that themortgage companies insist on an electrical survey. Theworstcasesare,however,inindustryandcommerce.

Periodic inspections are often requested by clients, reluctantly, to satisfy insurers or animpendingvisitbytheHSE.Eventhenitisusuallythecasethat‘youcan’tturnthatoff’or‘whycan’tyoujusttestthisbitandthenissueacertificateforthewholelot’.

Under the rare circumstances that an inspection and test is genuinely requested due toresponsibleconcernsforthesafetyofstaff,etc.,itisdifficulttoconvincetheclientthat,asthere are no drawings, or information about the installation, and that no switchgear islabelled,etc.,youaregoingtobeonsiteforaconsiderabletimeandataconsiderablecost.

When there are no drawings or items of information, especially on a large installation,theremaybeadegreeofexploratoryworktobecarriedoutinordertoensuresafetywhilstinspectingandtesting.Ifitisfeltthatitmaybeunsafetocontinuewiththeinspectionandtest, then drawings and information must be produced in order to avoid contraveningSection6oftheHealthandSafetyatWorkAct.

However, let us assume (in ourwildest dreams) that, aswith an Initial Verification, theoriginal installation was erected in accordance with the Wiring Regulations, and anyalterations and/or additions have been faithfully recorded and all the originaldocumentation/diagrams/charts,etc.arereadilyavailable!

Aperiodicinspectionandtestunderthesecircumstancesshouldberelativelyeasy,aslittledismantling of the installation will be necessary, and the bulk of the work will beinspection.

Inspection shouldbecarriedoutwith the supplydisconnectedas itmaybenecessary togainaccesstowiringinenclosures,etc.,andhencewithlargeinstallationsitwillprobablyneed considerable liaisonwith the client to arrange convenient times for interruptionofsuppliestovariouspartsoftheinstallation.

This is also the case when testing protective conductors, as these must never bedisconnectedunless thesupplycanbe isolated. It isparticularly important in thecaseofmainprotectivebondingconductorswhichneedtobedisconnectedinordertomeasureZe.

Ingeneralaninspectionshouldreveal:

1.Anyaspectsoftheinstallationthatmayimpairthesafetyofpersonsandlivestockagainsttheeffectsofelectricshockandburns.

2.Thattherearenoinstallationdefectsthatcouldgiverisetoheatandfire,andhencedamageproperty.

3.Thattheinstallationisnotdamagedordeterioratedsoastoimpairsafety.4.Thatanydefectsornon-compliancewiththeRegulations,whichmaygiveriseto

danger,areidentified.

Aswasmentionedearlier,dismantlingshouldbekepttoaminimumasthisprocessmaycreatefaults.Henceacertainamountofsamplingwillberequired.

Theamountofsamplingwouldneedtobecommensuratewiththenumberofdefectsbeingfound.

It should be noted that if an installation is effectively supervised in normal use, thenperiodicinspectionandtestingcanbereplacedbyregularmaintenancebyskilledpersons.This would only apply to, say, factory installations where there are permanentmaintenancestaff.

Questions

1. State few circumstances that would result in the need for a periodicinspection.

2.Statethreeinstallationconditionsthatmayneedinvestigation.3.Statethethreeitemsofdocumentationthatwillneedtisbe-completed.4. When may exploratory work be required before commencing a periodic

inspectionandtestofalargeinstallation?5.Whyshoulddismantlingbekepttoaminimum?6. When may periodic inspection and testing be replaced by routine

maintenance?

Answers

1.Anytwo,fromduedata,mortgage,insurance,etc.,2.AnythreefromSADCOWESlist.3.Periodic/conditionreport.4.Wherethereisalackofinformation/drawings,etc.,anditmaybeunsafeto

continuewithoutthem.

5.Toavoidcausingdamageandcreatingfaults.6.When the installation isundereffective supervisionand themaintenance is

carriedoutbyskilledpersons.

CHAPTER16Certification

Havingcompletedalltheinspectionchecksandcarriedoutalltherelevanttests,itremainsto document all this information. This is done on Electrical Installation Certificates,Electrical Installation Condition Reports, schedules, test results, Minor ElectricalInstallationWorksCertificates and any other documentation youwish to append to theforegoing.ExamplesofsuchdocumentationareshowninBS7671andthe IETGuidanceNote3oninspectionandtesting.

Thisdocumentationisvitallyimportant.Ithastobecorrectandsignedorauthenticatedbyacompetentperson.ElectricalInstallationCertificatesandElectricalInstallationConditionReportsmustbeaccompaniedbyascheduleoftestresultsandascheduleofinspectionsforthemtobevalid.ItshouldbenotedthatbothElectricalInstallationCertificatesandMinorElectrical InstallationWorksCertificates should be signed or otherwise authenticated bycompetentpersonsinrespectofthedesign,theconstructionandtheinspectionandtestingoftheinstallation.TheElectricalInstallationConditionReportissignedbytheinspector.

(For larger installations theremay bemore than one designer, hence the certificate hasspace for twosignatures, i.e.designer1anddesigner2.) Itcouldbe,ofcourse, that foraverysmallcompany,onepersonsignsallthreeparts.Whateverthecase,theoriginalmustbegiventothepersonorderingthework,andaduplicateretainedbythecontractor.

One important aspect of an EIC is the recommended interval between inspections. Thisshould be evaluated by the designer andwill depend on the type of installation and itsusage. In some cases the time interval ismandatory, especiallywhere environments aresubject to use by the public. The IET Guidance Note 3 give recommended maximumfrequenciesbetweeninspections.

An Electrical Installation Condition Report is very similar in part to an ElectricalInstallationCertificateinrespectofdetailsoftheinstallation,i.e.maximumdemand,typeofearthingsystem,Ze,etc.Therestoftheformdealswiththeextentandlimitationsoftheinspectionandtest,recommendations,andasummaryoftheinstallation.Therecordoftheextentandlimitationsoftheinspectionisveryimportant.Itmustbeagreedwiththeclientorotherthirdpartyexactlywhatpartsoftheinstallationwillbecoveredbythereportandthosethatwillnot.Theintervaluntilthenexttestisdeterminedbytheinspector.

Withregardtothescheduleoftestresults,testvaluesshouldberecordedunadjusted,anycompensationfortemperature,etc.beingmadeafterthetestingiscompleted.

AnyalterationsoradditionstoaninstallationwillbesubjecttotheissueofanElectricalInstallationCertificate,exceptwheretheadditionis,say,asinglepointaddedtoanexistingcircuit,whentheworkissubjecttotheissueofanMEIWC.

Summary:

1. The additionof points to existing circuits requires aMinorElectrical InstallationWorksCertificate.

2.AnewinstallationoranadditionoralterationthatcomprisesnewcircuitsrequiresanElectricalInstallationCertificate.

3.AnexistinginstallationrequiresanElectricalInstallationConditionReport.

NotePoints(2)and(3)mustbeaccompaniedbyascheduleoftestresultsandascheduleofinspections.

Astheclient/customeristoreceivetheoriginalsofanycertification,itisimportantthatallrelevantdetails are completed correctly.This ensures that future inspectors are awareoftheinstallationdetailsandtestresultswhichmayindicateaslowprogressivedeteriorationinsomeoralloftheinstallation.

Thesecertificates,etc.couldalsoformpartofa‘seller’spack’whenaclientwishestosellaproperty.

ThefollowingisageneralguidetocompletingthenecessarydocumentationandshouldbereadinconjunctionwiththeexamplesgiveninBS7671andtheIETGuidanceNote3.

ElectricalInstallationCertificate

1.Detailsofclient:Name:Fullname.Address:Fulladdressandpostcode.Description:Domestic,industrial,commercial.Extent:Whatworkhasbeencarriedout (e.g. fullrewire,newshowercircuit,etc.).Tickrelevantbox.

2.Designer/constructor/tester:Detailsofeachorcouldbeoneperson.Note: Departures are not faults, they are systems/equipment, etc. that are notdetailedinBS7671butmaybeperfectlysatisfactory.

3.Nexttest:Whenthenexttestshouldbecarriedoutanddecidedbythedesigner.

4.Supplycharacteristicsandearthingarrangements:Earthingsystem:Tickrelevantbox(TT,TN-S,etc.).Liveconductors:Tickrelevantboxes.Nominalvoltage:Obtainfromsupplier,butusually230Vsingle-phaseUandU0but400VUand230U0forthree-phase.Frequency:Fromsupplierbutusually50Hz.PFC:Fromsupplierormeasured.Supplierusuallygives16kA.Ze:Fromsupplierormeasurement.Supplierusuallygives0.8VforTN-S;0.35VforTN-C-Sand21VforTTsystems.Mainfuse:UsuallyBS1361,ratingdependsonmaximumdemand.

5.Particularsofinstallation:Meansofearthing:Tick‘supplier’sfacility’forTNsystems,‘earthelectrode’forTTsystems.Maximumdemand:Valuewithoutdiversity.Earthelectrode:MeasuredvalueorN/A.Earthingandbonding:Conductors:Actualsizesandmaterial,usuallycopper.Main switch or circuit breaker (could be separate units or part of a consumercontrolunit):BSnumber;Rating,currentandvoltage;Location;‘notaddress’;thatis,whereitislocatedinthebuilding;Fuseratingifinaswitch-fuse,elseN/A;RCDdetailsonlyifusedasamainswitch.

6.Commentsonexistinginstallation:Write down any defects found in other parts of the installationwhichmay havebeenrevealedduringanadditionoranalteration.

7.Schedules:Indicate the number of test and inspection ‘schedules that will accompany this

certificate’.

ElectricalInstallationConditionReport

1.Detailsofclient:Name:Fullname(couldbealandlord,etc.).Address:Fulladdressandpostcode(maybedifferenttotheinstallationaddress).Purpose:Forexample,duedate;changeofowner/tenant;changeofuse,etc.

2.Detailsofinstallation:Occupier:Couldbetheclientoratenant.Installation:Couldbethewholeorpart(givedetails).Address:Fullandpostcode.Description:Tickrelevantbox.Age:Ifnotknown,sayso,oreducatedguess.Alterations:Tickrelevantboxandinsertagewhereknown.Lastinspection:Insertdateor‘notknown’.Records:Tickrelevantbox.

3.Extentandlimitations:Full details of what is being tested (extent) and what is not (limitations). If notenoughspaceonformaddextrasheets.

4.Nextinspection:Filledinbyinspectorandsigned,etc.underdeclaration.

5.Supplydetails:AsperanElectricalInstallationCertificate.

6.Observations:Tickrelevantbox,ifworkisrequired,recorddetailsandenterrelevantcode(C1,C2,C3andF1)inspaceonright-handside.

7.Summary:Comment on overall condition. Only the identification of a code C1 or C2 willrequireaninstallationtobeclassifiedasbeingUNSATISFACTORY.

8.Schedules:Attachcompletedschedulesofinspectionsandtestresults.

ObservationCodes

C1Dangerpresent,immediateremedialactionrequired.Thisisusedwherethereis,forexample,anexposedlivepartthatcanbetouched.Itsissuggestedthatifpracticable,thisberectifiedondiscoverybut,ifnot,thentheownermustbeinformedinwritingasamatterofurgency.

C2Potentiallydangerous,urgentremedialactionrequired.This would be the case, say, wheremain protective bondingwas not present. Itwouldonlybecomedangerousiftherewasafaulttoearthandapersonhappenedtobesimultaneouslytouchingaccessibleexposedandextraneousconductiveparts.

C3Improvementrecommended.This would be used, for example, if there was a label missing for non-standardcolours.Itisanomissionbutitdoesnotmaketheinstallationunsafefortheuser.

F1Furtherinvestigationneededwithoutdelay.Thiswouldbe thecasewhenacodeC1orC2defect is suspectedbutbecauseofextentandlimitationsthecircuit/sinquestioncannotbeaccessed.

MinorElectricalInstallationWorksCertificate

Onlytobeusedwhensimpleadditionsoralterationsaremade,notwhenanewcircuitisadded.

1.Description:Fulldescriptionofwork.Address:Fulladdress.Date:Datewhenworkwascarriedout.Departures: These are not faults, they are systems/equipment, etc. that are notdetailedinBS7671butmaybeperfectlysatisfactory(thisisusuallyN/A).

2.Installationdetails:Earthing:Tickrelevantbox.Methodoffaultprotection:99%ofthetimethiswillbeautomaticdisconnectionofsupply.Protectivedevice:Entertypeandrating.Forexample,BSEN60898CBtypeB,20A.Comments:Noteanydefects/faults/omissionsinotherpartsoftheinstallationseenwhileconductingtheminorworks.

3.Tests:Earthcontinuity:MeasuredandthentickinboxifOK.Insulationresistance:Standardtestsandresults.EFLI(Zs):Standardtestsandresults.Polarity:StandardtestsandthentickinboxifOK.RCD:Standardtests,recordoperatingcurrentandtime.

4.DeclarationName,address,signature,etc.

ContentsofaTypicalScheduleofTestResults

1.Contractor: Fullnameoftester.2.Date: Dateoftest3.Signature: Signatureoftester.

4.Vulnerableequipment:Dimmers,electronictimers,CHcontrollers,etc.(i.e.anythingelectronic).

5.Address:Full,orifinalargeinstallation,thelocationofaparticularDB.

6.Zeatorigin: Measuredvalue.

7.RFC:RecordthehighestvaluethatisPEFCorPSCC(shouldbethesameforTN-C-S).

8.Confirmationofsupplypolarityandphasesequence:

Tickbox.

9.Instruments:Recordserialnumbersofeachinstrument,oronenumberforacompositeinstrument.

10.CircuitDescription: Detailsofcircuit,e.g.firstfloorlights.11.kVAratingofprotection: Takenfromdevice.

12.Typeandrating:Forexample,BSEN60898CBtypeB,32A,orBS8840A,etc.

13.Referencemethod: EnterA’,B’,‘C,‘100’,etc.14.Wiringconductors: Sizeofliveandcpc,e.g.2.5mm2/1.5mm2.15.Testresults: Enterallmeasuredresults,notcorrectedvalues.

ScheduleofInspections(asperBS7671)

ForEICsdonotleaveboxesuncompleted:N/Ainaboxifitisnotrelevant;inaboxifithas been inspected and is OK. For EICRs, the same as the EIC except when defects,omissions,etc.arefound,thenenteroneoftheappropriatecodesC1,C2,C3,orF1.

APPENDIX12394SamplePaper

SectionA

1.

a. For the initial verification of a new installation, list six items ofinformationregardingtheincomingsupplyandthreeitemsregardingtheinstallationthatshouldbemadeavailabletotheInspector.(9marks)

b. StatethethreereasonsfortheissueofanElectricalInstallationCertificate.(3marks)

c. State the documentation that must accompany an Electrical InstallationCertificate.(2marks)

d. State the Statutory document that relates to Inspection and Testing. (1mark)

2.

a. StatefourmethodsofprovidingBasicProtectiononly.(4marks)b. StatetwomethodsofprovidingbothBasicandFaultProtection.(2marks)c. Give an example of Electrical Separation in a domestic installation. (1

mark)d. StatetheIPcodesapplicabletoanaccessiblehorizontaltopsurfaceofan

enclosure.(2marks)e. State the conditions that would allow ‘routing of cables in prescribed

zones’tobeusedastheonlymethodofprotectionwherecablesareburiedlessthan50mmfromthesurfaceofawall.(3marks)

f. Statethethreeteststhatrequiretheuseofalow-resistanceohmmeter.(3marks)

3.

a. Explain,withregardtoringfinalcircuitcontinuity

i. why,whenLsandNshavebeencrossconnected,thereadingsateachsocketmayvaryconsiderablyaroundthering;(2marks)

ii. thesignificanceofthehighestreadingwhenLandcpcaretestedateachsocket.(2marks)

b.Listthefirstfivetests,asperBS7671:2008,tobeconductedonanewlightindustrialunitwhereallcircuitsareradials.ThesupplyearthingsystemisTN-C-S.(5marks)

c.Statetwomethodsofprovidingadditionalprotection.(2marks)d.ExplainindetailwhyanRCDtestshouldnotbeconductedbeforeanearth

faultloopimpedancetest.(4marks)

SectionB

Allquestionsinthissectionrelatetothefollowingscenario:

Avillagecricketclubhashadanewclubhousebuiltcomprisingchangingrooms,amainoffice, a loungeandbararea, aplayers’waitingandviewingarea, andmaleand femaletoiletsandshowerfacilities.

Thebuilding isa traditionalbrickand timberconstructionwith internalblockwalls.Allcables are 70°C thermoplastic flat sheathed 6242/3Y, ‘chased in’ to full plaster depth andaccessoriesare flushmounted.AllcircuitsareRCBOprotectedtoBSEN61009-1 typeB.Themainprotectivebondingtogasandwaterservices is10mm2copper.Themaximumlengthofthisbondingconductoris10m.

Thesupplyis230V50Hzsingle-phaseandtheearthingsystemisTN-C-SwithameasuredZevalueof0.23ΩandaPFCof1kA.Thedistributionfuseboardis12-waymetal-clad.

TableA1.1givescircuitdetails,TableA1.2indicatesconductorresistances.

Alltestsarecarriedoutat20°C.

TableA1.1

TableA1.2

ConductorSizemm2 ResistanceinmΩ/mat20°C1.0 18.11.5 12.12.5 7.416.0 3.08

10.0 1.83

4.

a. Statethemethodusedforprotectionagainstshockforthisinstallation.(2marks)

b. Explainwhythelighting,cookerandhanddryercircuitshavebeenRCDprotected.(4marks)

c. Explaintheconsiderationstobemaderegardingtheentryofthemaintailsandearthingconductorintothedistributionboard.(5marks)

d. Determine the expected resistance R2 of the main protective bondingconductor.(4marks)

5.

a. Thekitchenringfinalcircuithasbeensecurelyisolated.Describeindetailhowaringfinalcircuitcontinuitytestwouldbecarriedout.(10marks)

b. Whatwouldbe:

i. the expected L toN resistance at each socket after correct L–Ncross-connection?(2marks)

ii. theexpectedLtocpcresistanceateachsocketaftercorrectL–cpccrossconnection?(3marks)

6.

a. Drawafullylabelleddiagramoftheearthfaultlooppathforcircuit5.(8marks)

b. Explainwhy the PEFC and the PSCC for this installationwould be thesamevalue.(2marks)

c. DeterminetheexpectedZsvaluesforcircuits1,6and9andconfirmiftheyareacceptable.(5marks)

2395SamplePaper

SectionA

1.

a. Statethefourresponsibilitiesofaninspectorwhilstcarryingoutaperiodicinspectionandtestofaninstallation.(4)

b. Statetheactiontobetakenbyaninspectorpriortocarryingoutaperiodicinspection and test of a complex installation, where no diagrams,drawings,charts,etc.areavailable.(5)

c. List the three documents that must be completed for the periodicinspectionandtestofaninstallation.(3)

d. StateoneStatutoryand twonon-statutorypublications thatwouldapplytotheperiodicinspectionandtestofaninstallation.(3)

2.

a. State the human senses that would be used when inspecting a metalconduitsystemina30-year-oldinstallation.(2)

b. List three considerations thatwoulddetermine the frequencyofperiodicinspectionandtestingofaninstallation.(3)

c. ListthreerequirementsofH&SEGS38regardinginstrumenttestleads.(3)d. Describetheprocedureforthesafeisolationofsupplies.(7)

3.

a. State the action to be taken, giving reasons, regarding the earthingconductorduringatestofexternalearthfaultloopimpedance.(2)

b. Determine, from the following test results,whichcircuitsdonot complywiththerequirementsofBS7671(showallcalculations):

CircuitNo. MeasuredZsΩ MaximumTabulatedZsΩ1 1.37 1.752 2.15 2.733 0.68 0.874 6.0 7.285 1.72 2.186 0.5 0.54

(3)

c. Describe, indicating all test values, the procedure for carrying out aninstrumenttestona20mARCDusedforadditionalprotection.(10)

SectionB

A small 30-year-old dry-powder coating company is situated adjacent to an 11 kV/400V/230VDistributionNetworkOperator’ssubstation.TheearthingsystemisT.N-C-Swithanexternalearthfaultloopimpedance(Ze)of0.015andaprospectivefaultcurrent(PFC)of15kA.TheSupplyisthree-phasefourwirewith100ABS1361fusesandtheservicetailsare35mm2witha25mm2earthingconductor.

Gas andwater services are located some 30m from the electricity intake and nomainprotectivebondingconductorsarepresent.

Attheintakeposition,aTP&Ndistributionboard,housingBS88fuses,isusedtosupplyallfinalcircuitsinthefactoryarea.AnSP&NconsumerunithousingBS3036fusesislocatednexttothedistributionboardandsuppliesfinalcircuitsinasmallkitchenarea.

The wiring system throughout is 70°C thermoplastic, copper single core conductorsenclosedinmetaltrunkingandconduit.

Theprocessofdry-powdercoatingofmetalpartsinvolvestheuseofacidbaths,waterjets,atunnelovenandelectrostaticallychargedpowderspraying.

Newownershaverequestedaperiodicinspectionandtestofthewholeinstallationbeforetheycontinuewiththeproductionprocesses.

Alloriginaldocumentation,diagrams,charts,etc.havebeenlost.

Alltestingiscarriedoutatatemperatureof20°C.

TableA1.3givesresistancevaluesofcopperconductorsat20°C.

TableA1.3Conductorresistance

Conductorcsamm2 mΩ/mat20°C1.5 12.12.5 7.414.0 4.616.0 3.0810.0 1.8316.0 1.15

4.

a. State three considerations to be made by the inspector in order todeterminetheinitialamountofsamplingtobecarriedout.(3)

b. Explain the circumstances thatmay require an increase in the samplingrateabovetheinitialamountdetermined.(3)

c. Statethreecircumstanceswherecableswouldnotbeinspectedandwould,

therefore, not be included in the extent and limitations section of theElectricalInstallationConditionReport.(3)

d. List,apartfromage, threegeneralareasof investigationtobeconsideredbytheinspectorcarryingouttheinspectionofthisinstallation.(3)

e. State three external influences that should be considered for thisinstallation.(3)

5.

a. Explain why the protective devices in the SP&N consumer unit do notcomplywithBS7671:2008.Indicatetheclassificationcodetoberecorded.(5)

b. State the cross-sectional area of themain protective bonding conductorsthatshouldbeinstalled,theclassificationcodetoberecordedduetotheiromission,andtheexpectedtestresistanceiftheywereinstalled.(6)

c. List, apart from socket outlets not exceeding 20 A, four situations thatrequireadditionalprotectionbyRCDs.(4)

6.

a. Describehowa test forcpccontinuity,henceobtainingavalue for (R1+R2),wouldbecarriedoutonaradialcircuitsupplyingsingle-phasespray-boothmotor.Thiscircuithasbeencorrectlyisolatedatitsorigin.(9)

b. Calculatetheexpectedvoltagedropinthemotorcircuitin(a)above,ifthemotor has a design current of 20 A and is supplied by 4 mm2 liveconductorswithameasuredlinetoneutralresistanceof0.15Ω.(6)

APPENDIX22394SamplePaper(Answers)

SectionA

1.

a. anysixfrom:EarthingsystemNumberandtypeofliveconductorsVoltageFrequencyPFCZe

TypeandratingofsupplyprotectivedeviceAnythreefrom:Typeandcompositionofwiring,type,numberofpoints,etc.MethodoffaultprotectionIdentificationofprotectivedevices,andisolators,switches,etc.DetailsofcircuitsorequipmentvulnerabletoatypicaltestDetailsofprotectivebondingconductors

b. Newinstallation;Addition;Alterationc. Scheduleoftestresults;Scheduleofinspectionsd. EAWR

2.

a. Insulation;Barriersorenclosures;Obstacles;Placingoutofreachb. SELV;PELV;Doubleinsulation;Reinforcedinsulation(anytwo)c. Shaverpointd. IPXXDorIP4Xe. Installationmustbeunderthesupervisionofaskilledorinstructedpersonf. Continuityorprotectiveconductors;Ringcircuitcontinuity;Deadpolarity

3.

a.

i. Incorrectcross-connectionii. R1+R2forthering

b.Continuityofprotectiveconductors

i. Insulationresistanceii. Polarityiii. Earthfaultloopimpedance

iv. OperationofRCDs

c.RCD;Supplementaryequipotentialbondingd.IftheRCDtestwasdonefirstandtheearthlooppathwastoohigh,afault

would have been placed on the circuit and the RCD may not operate,placingeveryoneatrisk

SectionB

4.

a. Automaticdisconnectionofsupplyb. These circuits only need RCD protection because the cables supplying

themarelessthan50mmfromthesurfaceofthewallsc. The tails and earthing conductor should enter theDB through the same

holetoavoidelectromagneticeffects.TheentryholeshouldbetoIPXXDorIP4Xiftopentry,IPXXBorIP2Xelsewhereandcablesprotectedagainstmechanicaldamage.

d. 10mof10mm2bondingconductor 1000

5.

a.

Selectalow-resistanceohmmeterCheckfordamageandbatteryconditionandcurrentcalibrationNullorzerotestleads(GS38leads)IdentifylegsofringMeasureindividualloops,r1,rnandr2Cross-connectoppositeLsandNsMeasurebetweenLandNateachsocket(shouldbethesamevalue)RepeatwithLsandcpcscrossed(highestreadingisR1+R2)Record(R1+R2)Reinstatesystem

b. i.r1andrneach soreadingateachsocket

ii. soreadingateachsocket

6.a.

4marksfordiagram,4marksforlabels(halfeach)NOMARKSIFDIAGRAMINCORRECT

b.Theearthfaultcurrentandtheshort-circuitcurrenttakethesamepath,i.ethePENconductor

c.

Zs=0.23+0.1=0.33Ωok,0.8×maxis1.09Ω

Zs=0.23+0.13=0.36Ωok,0.8×maxis1.75Ω

Zs=0.23+0.58=0.81Ωok,0.8×maxis5.83Ω

2395SamplePaper(Answers)

SectionA

1.

a. Ensuretheirownsafetyandthatofothers,etc.(1)Compareresultswithrelevantcriteria(1)ConfirmcompliancewithBS7671(1)Takeaviewoftheconditionoftheinstallation(1)(4marks)

b. Exploratorysurveytoestablishifsafetocarryoutinspectionandtestingwithoutdiagrams/drawings,etc. Ifnot,thentheclientcanberequiredtoproducethem.(5marks)

c. EICR,schedulesofinspectionsandschedulesoftestresults(3marks)d. EAWR,BS7671,GN3,On-siteguide,etc.(3marks)

2.

a. Touchandsight(2marks)b. Typeofinstallationandequipment;useofinstallation;externalinfluences;

qualityandfrequencyofmaintenance(anythree)(3marks)c. Nomorethan4mmprobetips;fingerguards;coloured;suitablyinsulated;

fused;suitablelength(anyfour)(3marks)d. Seekpermissiontoisolate(1)

Isolateandlockoff(1)Retainkey(1)SelectanapprovedvoltageindicatortoGS38(1)Proveindicatoronknownsupplywithsamevoltageassystemundertest(1)Checksystemisde-energized(1)Reprovevoltageindicator(1)(7marks)

3.

a. Disconnecttoavoidparallelpaths(2marks)

CircuitNo. MeasuredZsΩ CorrectedMaximumZsΩ1 1.37 1.75x0.8=1.42 2.15 2.73x0.8=2.183 0.68 0.87x0.8=0.74 6.0 7.28x0.8=5.825 1.72 2.18x0.8=1.746 0.5 0.54x0.8=0.43

b. Circuits4and6donotcomply(3marks)

c. Ensureearthingissatisfactory(1)SelectRCDtester(1)CheckleadsaretoGS38(1)ConnectleadstoL,NandEonloadsideofRCD(1)Testat20mAonboth0°and180°(1)CheckRCDtripswithin300ms(1)Recordlongesttime(1)Repeattestat100mAonboth0°and180°(1)CheckRCDtripswithin40ms(1)Recordlongesttime(1)(10marks)

SectionB

4.

a. Anythreefromtheliston‘Settinginspectionandtestingsamples’GN3(3marks)

b. Ifinspectionortestingoftheoriginalsamplerevealspoorresults(3marks)c. Cables in conduit or trunking; under floors; in roof spaces; within the

buildingfabricorunderground(anythree)(3marks)d. AnyotherthreefromtheSADCOWESlist(3marks)e. Water;dust;corrosion;heat(Anythree)(3marks)

5.

a. BS3036fuseshaveaverylowbreakingcapacity(4kAmax)andthePSCCattheorigin,wherethesefusesarelocated,is15kA;henceashort-circuiton any of the circuits fed by these fuses is likely to cause seriousdamage/arcing/fireintheSP&Nconsumerunit(5marks)

b. 10mm2;C2; (6marks)c. Circuitssupplyingmobileequipmentnotexceeding32A,outdoors;Cables

inwallslessthan50mm;AllLVcircuitsinbathrooms;Circuitsinsaunas;Swimmingpools;Agriculturallocations,etc.(4marks)

6.

a. Isolate/disconnectatmotorendofcircuit(1)Selectalow-resistanceohmmeter(1)Checkforinstrumentdamage(1)Checkbatterycondition(1)CheckleadsaretoGS38(1)LinklinetocpcatDBormotor(1)Testbetweenlineandcpcatotherend(1)RecordresultReinstatesystem(1)(9marks)

b. Circuitresistance=0.15×1.2=0.18ΩMotorcurrent=20AVoltdrop=20×0.15×1.2=3.6volts(6marks)

APPENDIX32394/5SampleMCQPaperandAnswers

1. InordertocomplywithBS7671,whichoneofthefollowingshouldaninspectorbe?

a. Anapprovedcontractorb. Acompetentpersonc. Aqualifiedelectriciand. Aninstructedperson

2.Whichoneofthefollowingfulfilstherequirementforsafeisolationofacircuit?

a. Switchoffandinformallpersonnelb. Switchoffanddisplaynoticesc. Lockoffanddisplaynoticesd. Lockoffandgivekeytoclient

3. Which one of the following is the correct procedure for the use of a voltageindicatorwhencarryingoutsafeisolation?

a. Checktheindicatorviaitsowntestbuttonb. Checktheindicatorontheisolatedcircuitc. Checktheindicatoronaprovingunitd. Checktheindicatorisconnectedtoearth

4.Whichoneofthefollowingisthecorrectactionforaninspectoraftercompletingthesafeisolationofacircuit?

a. Keepthekeyinatool-boxb. Handkeytotheclientc. Giveduplicatekeytoclientd. Keepkeyonperson

5.Thesupplytoanofficecomplexistobeisolatedinordertocarryoutaninspectionand test.Which one of the following is the inspector’s first step in the isolationprocess?

a. Switchoffandprovedeadb. Seekpermissiontoisolate

c. Carryoutacontinuitytestd. Informtheenergysupplier

6.ApropertywhichincludesasolarPVsystemistobeinspectedandtested.Whichoneofthefollowingactionsmustbetakentoensuresafeisolation?

a. IsolatebothmainandPVsuppliesb. IsolatePVsupplyonlyc. Isolatemainsupplyonlyd. LinkoutthePVmetering

7.Whichoneofthefollowingcanonlybeconductedwiththesupplyisolated?

a. RCDtestb. Phaserotationatamotorc. Ringfinalcircuitcontinuityd. Earthfaultloopimpedance

8.WhichoneofthefollowingisthestatusofBS7671?

a. Statutoryb. Non-statutoryc. Advisoryd. Mandatory

9. Which one of the following would be the most suitable as a reference for aninspectorconductinganinspectionandtest?

a. BS7671b. GS38c. EAWRd. GN3

10.Whichoneofthefollowingdocumentsrequiresthedetailsofthemethodoffaultprotection?

a. Electricalinstallationcertificateb. Electricalinstallationconditionreportc. Minorworkscertificated. Scheduleoftestresults

11.GS38requiresthatlowvoltagetestleadsshouldbe:

a. fused,havefingerguardsandnomorethan4mmexposedtipsb. fused,havefingerguardsandmorethan4mmexposedtipsc. non-fused,havefingerguardsandnomorethan4mmexposedtipsd. non-fused,havefingerguardsandnomorethan2mmexposedtips

12. Which one of the following is the instrument to be used for an insulationresistancetest?

a. Aresistancetesterb. Ahigh-readingohmmeterc. anohmmeterd. aninsulationresistancetester

13.WhichoneofthefollowingunitsisdisplayedonanRCDtester?

a. msb. Msc. mAd. MΩ

14.Thetechnicalspecificationforalow-resistanceohmmeterrequirestheinstrumenttodeliverano-loadvoltageandashort-circuitcurrent:

a. between4V–24Va.c.;notexceeding200mAb. between4V–24Vd.c.;notlessthan100mAc. between4V–24Va.c.ord.c.;notlessthan200mAd. between4V–24Va.c.ord.c.;notexceeding200mA

15. The following tests are to be conducted on an installation: i. Earth fault loopimpedance;ii.RCDoperation;iii.Continuityofprotectiveconductors;iv.insulationresistance.Whichoneofthefollowingisthecorrectsequenceforthesetests?

a. 1,2,3,4b. 3,2,1,4c. 4,3,2,1d. 3,4,1,2

16.Which one of the following tests automatically conducts a dead circuit polaritytest?

a. Insulationresistanceb. Ringfinalcircuitcontinuityc. Protectivebondingcontinuity

d. RCDoperation

17.Whichoneofthefollowingtestsrequirestheinstrumentleadstobetested‘open’and‘shorted’beforetestingcommences?

a. Insulationresistanceb. Conductorcontinuityc. RCDoperationd. Polarity

18.Whichoneofthefollowinggivesdetailsofthecorrectuseofavoltageindicator?

a. GN3b. BS7671c. GS38d. EAWR

19. In order to significantly reduce the risk of electric shock under ‘fault-free’conditions,itisimportantthat:

a. disconnectiontimesaremetb. basicprotectionisprovidedc. theearthingconductoris≥6.0mm2

d. a‘non-standardcolours’noticeisdisplayed

20. A test for continuity of a main protective bonding conductor requires itsdisconnectionatoneend.Thisistoeliminate:

a. theriskofshockduringthetestb. thetestleadresistancec. excessivevoltdropduringthetestd. theintroductionofparallelpaths

21.Whichoneofthefollowingwouldbetheeffectontheresistanceofacableifbothitscsaandlengthweredoubled?

a. Halvedb. Stayedthesamec. Doubledd. Quadrupled

22.Alengthof2.5mm2flatsheathedcablehasend-to-endliveconductorresistancesof0.37Ω.Whichoneofthefollowingwouldbetheapproximateresistanceofthe

associated1.5mm2cpc?

a. 1.67Ωb. 1.48Ωc. 0,62Ωd. 0.19Ω

23.Whichoneofthefollowingwouldbetheoverallvalueofinsulationresistanceofaninstallationifindividualcircuitvalueswere10MΩ;

MΩ;25MΩand45MΩ?

a. 95MΩb. 23.75MΩc. 4.37MΩd. 0.23MΩ

24.Whichoneofthefollowingwouldnotberecordedonascheduleoftestresultsforaringfinalcircuitcontinuitytest?

a. r1b. rnc. LtoNateachsocketd. Ltocpcateachsocket

25.Whichoneofthefollowingwouldbetheeffectontheinsulationresistanceofacableifbothitscsaandlengthweredoubled?

a. Halvedb. Stayedthesamec. Doubledd. Quadrupled

26.WhichoneofthefollowingearthingsystemsincludesaPENconductor?

a. TTb. TN-Sc. ITd. TN-C-S

27.Whenconductinganearth electrode resistance testonagenerator electrode, anacceptable value should be the average of three readings and an instrumentaccuracyof:

a. 100%b. >5%c. >2%d. ≤2%

28.Anexternalearthfaultloopimpedancetestmustbecarriedoutwiththeearthingconductor:

a. disconnectedandtheinstallationenergizedb. connectedandtheinstallationenergizedc. disconnectedandtheinstallationisolatedd. connectedandtheinstallationisolated

29. When conducting an earth fault loop impedance test on a radial circuit theearthingconductoroftheinstallationmustbe:

a. disconnectedandallprotectivebondingconductorsinplaceb. disconnectedandallprotectivebondingconductorsdisconnectedc. connectedandallprotectivebondingconductorsinplaced. connectedandallprotectivebondingconductorsdisconnected

30. Which one of the following would be the maximum value of Zs permitted toachievetherequireddisconnectiontime, foramaximummeasuredvalueofearthfaultloopimpedanceof1.15Ω?

a. 2.3Ωb. 1.92Ωc. 1.44Ωd. 0.92Ω

31. Which one of the following needs to be compensated for when comparingmeasuredvaluesofZswithmaximumtabulatedvalues?

a. Cablelengthb. Cablecsac. Changeintemperatured. Typeofprotectivedevice

32.ThevalueofZs tobe recorded for anearth fault loop impedance testona ringfinalcircuitisthevaluemeasuredatasocketoutlet:

a. nearestthedistributionboardb. thatgivesthehighestreading

c. nearestthemidpointoftheringd. thatgivesthelowestreading

33. Which one of the following is the requirement for RCDs used for additionalprotection?

a. >30mAandtrippingin40msat5×IΔn

b. ≤30mAandtrippingin40msat5×IΔn

c. <30mAandtrippingin40msat5×IΔn

d. ≥30mAandtrippingin300msat5×IΔn

34.Whichoneof the following is themaximumtestcurrent required fora300mARCDinstalledforprotectionagainstfire?

a. 1500mAb. 300mAc. 100mAd. 30mA

35. Which one of the following is the rating of an RCD installed for additionalprotectionifthemaximumtestcurrentis100mA?

a. 100mAb. 30mAc. 20mAd. 10mA

36.Whenconductingaprospectivefaultcurrent testat theoriginofan installation,theearthingconductormustbe:

a. disconnectedb. linkedtotheneutralc. connectedd. excludedfromthetest

37.Aprospectivefaultcurrenttestattheoriginofathree-phaseinstallationgavethefollowingresults:PEFC–4.7kA;PSCC–5.5kA.Whichoneofthefollowingwouldberecordedonascheduleoftestresults?

a. 11kAb. 10.2kAc. 5.5kAd. 4.7kA

38.ItisrecommendedthatafunctionaltestonanRCDviaitsintegraltestbutton,becarriedout:

a. annuallyb. half-yearlyc. everythreemonthsd. everyfourmonths

39.Disconnectiontimesexceedingthepermittedmaximumvaluesareadirectresultof:

a. insulationresistancevaluesapproachingtheirminimumb. poorlyconnectedmainprotectivebondingconductorsc. earthfaultloopimpedancevaluesexceedingBS7671requirementsd. earthfaultloopimpedancevaluesunacceptablylow

40.Aleakagecurrentof11mAbetweenLandEoccurringina230VcircuitwouldbetheresultofaL–Einsulationresistancevalueof:

a. 2.53MΩb. 0.02MΩc. 0.5MΩd. 1.0MΩ

Answers

1b 11a 21b 31c2c 12d 22c 32b3c 13a 23c 33b4d 14c 24c 34b5b 15d 25a 35c6a 16b 26d 36c7c 17a 27d 37a8b 18c 28c 38c9d 19b 29c 39c10c 20d 30c 40b

IndexPagenumbersinitalicsdenoteanillustration,boldindicatesatable

A

additionalprotectionxi–xii,xv–xvi,55–8,56

additionsandalterations4,5,11,68,74

ambienttemperaturecorrection49

approvedtestlamp(voltageindicator)8,9

B

barriersandenclosuresxix,35,36

basicprotectionxii,xv–xvi

BSfingertest35,36

BuildingRegulationsPartP4–5

C

certification:competency5,73;documents2,5,73–6;observationcodes77

circuitbreakers13,59

City&Guilds2394course:sampleMCQpaper&answers95–103;samplepaper81–4,82–3;samplepaper(answers)89–91

City&Guilds2395course:sampleMCQpaper&answers95–103;samplepaper85–8,87;samplepaper(answers)92–4

ClassIIequipmentxvi

conductoroperatingtemperature49

conductorresistance49

continuityofprotectiveconductors17–20,18,19–20

continuityofringfinalcircuitconductors23–7,24–7,27

continuitytesters6

D

dutyholdersxii,3–4

E

earthelectroderesistance:earthfault loopimpedancetest44–5;electrodeinstallation42; potentialdivider42,43–4, 44;

resistancearea41–2,43;tester7

earthfaultloopimpedancetest:earthelectroderesistance44–5;earthfaultlooppath47,48;externalloopimpedanceZe

49;methodandcalculationprocess48–9,50–2

earth-freelocalequipotentialbondingxvii

Edisonscrewtypelampholder37

ElectricalInstallationCertificate(EIC)5,11,73–6,79

ElectricalInstallationConditionReport(EICR)2,5,69,73–4,76–7,79

electricalseparationxvii,xvii,xix

electricalsystemsandequipmentxii,3–4

ElectricityatWorkRegulations(EAWR)19893–4,9

electricshock:IPCodesxviii–xix;protectionmeasuresxv–xvii,xvii,xix;risklevelsxiii–xv,xiv

electricsystemsandequipment3–4

exposedconductivepartxii,xvi

extentandlimitations73–4

externalloopimpedanceZe49

extraneousconductivepartxii,xvi

F

faultprotectionxi,xvi

functionaltesting63

I

Icnrating59

IETwiringregulations2–3

initialverification2,11–14

inspectionschedule2,11,69,73,79

insulationresistance29–32,30,31

insulationresistancetester6

IPCodesxviii–xix,xix

L

lightingcircuits20,37,38,38

LocalBuildingControlAuthority(LABC)4,5

loopimpedancetester7

low-resistance ohmmeters: protective conductors 18, 19–20, 19–20; ring final circuit conductors 23–7, 24–7, 27; test

instrument6

M

meggeringseeinsulationresistance

MinorElectricalInstallationWorksCertificate(MEIWC)2,5,73–4,77–8

N

non-conductinglocationxvi–xvii,35

non-statutoryregulations2–3

P

periodicinspectionandtesting2,67–71

PeriodicInspectionReport(PIR)2

PFCtester8

phasesequenceindicator61,61

polarity37–8,38

potentialdivider42,43–4,44

prospectivefaultcurrent(PFC/PSCC)59

protectiveconductorsxiii

protectiveequipotentialbondingxvi

provingunit8

R

radialsocketoutletcircuits38

RCDs:additionalprotectionxv–xvi;earthfaultloopimpedancetest45,49,55;operationaltest55–6,56;requirementsfor

protection56–8;testinstrument7

S

SELVxv,31,31

statutoryregulationsxi,2

supplypolarity38

T

testinstruments5–9,9

testresultsschedule2,11,69,73,74,78–9

testsequence:initialverification12–13;periodicinspectionandtesting67–70

V

voltagedrop65,66