Introductiontoswitchgearassembliesandcontrolpanels,PartI Wherearetheseassembliesused?Switchgearandcontrolpanelsarefoundinpowergenerating stations,transformerstations,distributionsubstations,commercialandinstitutionalbuildings,industrial plantsandfactories,refineries,papermills,metalsmeltersandanyotherplacewhereelectricenergyis utilizedorelectricpowerisdistributedtoanynumberofzones.Thereareafewcommontypesof assembliesthatcoveralmostanyapplication.Abroadclassificationaccordingtothelocationofthe switchgearassembliesiswhetherthegearisinstalledindoororoutdoor.Afurtherclassificationforthe indoorgearisstandardventilatedindoor,indoorwithdriphood,indoorforlocationinsprinklersarea, indoorinhazardouslocation,arcproof(typea,borc)andindoorincorrosiveenvironment.Outdoor switchgearcanalsobefurtherclassifiedaswhetherithasanisleornot(walkinvs.nonwalkintypes) withorwithoutaworkingarea.Anothermethodofclassifyingageariswhetheritisabottomortop entry,thepowerandcontrolcablesareenteringfromthebottomorthetopofthegear.Theswitchgear cancontainasswitching/interruptingdevice(s):acircuitbreaker(c.b.),aswitch/fusecombination,a contactor/fusecombination(formotorswitching),forlowvoltage(l.v.)assemblies:aswitchorbreakerin serieswithacontactor(formotorswitching).Certainconfigurationscomeonlyasnondrawout construction,othersasdrawout.Ifspecialrequirementsforthegearareneeded,thespecialproperty canbeusedasacriteriafordefiningthegear,forexample,ifdusttightenclosureisrequiredduetothe presenceofdust(fineorcourse)intheatmospherethisgearisdesignatedasdusttight.Forswitchgear assemblies,asheatisgeneratedfromthehighcurrentflowing,adusttightenclosureisalmost impossiblethusadustproofoneisused,instead.Themajorstandardsthatgovernthedesign, manufacture&testingoftheseassembliesare:CSA,ANSI,IEC,EEMAC,NEMA. Switchgearassemblies&motorcontrolcenters(starters)lineupscanbeclassifiedaccordingtotheir voltageclasses.Thel.v.equipmentisratedintherangeof120/208Vsingleorthreephaseto750VAC. Themediumvoltageonesare2400/4160Vto44KV.Theenclosuresforalllowvoltageconstructionare metalenclosed.Someconstructionsincludepartitionsandbarrierstogiveasaferoperationoverand abovethestandardconstruction.Formediumvoltagegearbothconstructiontypes,metalcladandmetal enclosed,arecommon. Inthissectionthemajorcomponentsoftheswitchgearassemblies,motorstartersandassociated ancillarieswillbegiven.Forl.v.switchgearassemblies:moldedcaseorpower(airmagnetic)circuit breakers(drawoutorfixed)completewithorwithoutintegralovercurrentprotectiondevice(thermal magnetic,solidstateormicroprocessorbased)withorwithoutzoneinterlockingprovision,cradlefor drawoutversionsonly,fixedpotentialandcontrolpowertransformers,currenttransformers,interframe andbackbarriers,mainbusbars,runbacks,busrisers,cablelugs(compressionormechanical), protectivefusesforbreakercontrolcircuits,instrumentcompartments,breakeraccessories,breaker liftingdevices(integralwithgear),fusedorunfusedinterrupterswitches,protective/monitoring/ auxiliaryrelays,meteringdevices(ammeters,voltmeters,watthourmeters/wattmetersanddigital meteringpackagesD.M.P.),controlswitchesandindicatinglights.Formediumvoltageswitchgear assemblies,themaincomponentsare:drawoutcircuitbreakers(oil,air,SF6,vacuum),switching device(loadbreakordisconnect)withorw/ofuses(powercurrentlimitingorpowerexpulsiontype)

withorw/oblownfuseindicator/actuator,instrumenttransformers,capacitortrippingdevice,relays, meters&instruments,mainbus,control&indicatingdevices,jumpers,cablelugs,cablesupports, potheads,barriers,shutters,instrumentcompartments,testswitchesandbreakeraccessories. Forl.v.motorcontrolcentersthecomponentsare:combinationmotorstarters,instrument transformers,motorprotectiondevices,mainbus,cableentrycompartments,verticalbus,control cables,pushbuttons,pilotlights,breakerorswitchhandle,mountingpansandprogrammablelogic controllersplc(processormodule,I/O,networkinterfaceandotherassociatedmodules). Form.v.starters,thecomponentsare:contactors(vacuum&air),fusedcontroltransformer,overload protection,currenttransformers,instrumentcompartments,meters,auxilliaryrelays,timers,control devices,multifunctionmotorprotectionrelays,indicatinglights,powerfusesandsurgearresters. Thereareafewdistincttypesofswitchgearcubiclesandarelistedhereafter:incoming(main) cubicles,transformerfeeders,bustie(sectionalization),generatorexcitercontrol,generatorneutral cubicles,inductionmotorcontrolcubicle,synchronousmotorswitchingboardandpotentialtransformer cubicles(usedinconjunctionwithisolatedphasebusingeneratingstations). Othercomponentsthatcouldbeseenattachedorconnectedtoswitchgearlineupseitherornottoform aunitsubstationare:powertransformers,lowvoltagebusduct/mediumvoltagebusorcableductruns. Ifthetransformersareclosecoupledandinstalledindoor,thendrytypetransformersareused.Ifthey arelocatedoutdoorandconnectedtotheswitchgearbynonsegregatedbusductorcableductorbya throat(witho/dswitchgear)thantheyareoftheoilfilledtype.Anothertypeoftransformersthatcanbe foundindoorsisthecastresincoiltype.Othercomponentsthatareneededfortheproperoperationof theswitchgearorcontrolpanelbutnotnecessarilypartoftheinstallationormaybeinstalledremotely are:thebatteriesthatsupplycontrolpowerfortheproperoperationofthecircuitbreakers,protection devices,meteringpackagesandcontroldevices.Theycouldbeleadacidornickelcadmiumcomplete withachargersystemsizedandratedtooperateallloadsundernormalandpowerlossconditions. Thestationarybatteryisdesignedtoserveasanauxiliary/standbysourceofpowertoalldevices connectedtoit.Thebatteryisnormallymountedonracksandiscontinuouslychargedexceptfor intermittentdischargingintervalsofvaryingtimesandpower.Batteryvoltagegraduallydeclinesduring dischargeandshouldnotbepermittedtodropbelowtheminimumtoleratedbytheloadplustheline drop.Toprotectthebatteryagainstoverdischargealowvoltagerelay(d.c.)isrecommendedaspartof theinstallation.Therateofvoltagedeclinedependsupon:thedemandcurrentoftheload,durationof thedischarge,chemicaldesignandtypeofcells,numberandsizeofplatesineachcell,batterystateof chargeatbeginningofdischarge,ageofbatterycellsandtemperatureofcells.Thecapacityofthe batteryisbasicallyitsabilitytosupplyagivencurrentforagivenperiodoftimeatagivencell temperaturewithoutgoingbelowtheminimumvoltage(batteriesareratedinamperehouratagiven dischargerate).Stationarybatteriesareusuallyratedfor8hour,3hour,1hour,1minutedischarge.The amperehourratingissimplytheproductofthedischargeinamperesmultipliedbythegivendischarge timeperiod.Inthenextfewparagraphsthetypesofplatesandgridalloysfortheleadacidand alkaline(NiCad),theelectrolyteproperties,batterycharging,batterysafetyandfinallybattery maintenancewillbecovered. Fortheleadacidbattery,thepositiveplatesavailableare:thepasted(Faure)platewhichcomprisesofa

latticeworkmetallicgridwiththeopeningsfilledwithleadoxidepaste.Thegridmaybemadeupof leadantimonyorleadcalcium,thepropertiesofwhichwillbegivenlater.Thesecondtypeisthe multitubularplates,whichuseporousplatestocontaintheleadoxide.Thegrid(leadantimony)is basicallyarowofspinesextendingfromthetopbartothebottomcapbar.Poroustubesfilledwithlead oxide(powdered)withthegridformsthepositiveplate.ThisdesignformprvidesmoreAHofcapacity percubicfootofbatteryvolumeatmoderateratesofdischarge.Thethirdandlasttypeistheplante typewhichisconsideredtohavethelongestlifeexpectancyofallleadacidstationarybatterydesigns. Thepositiveplateconsistsofagrid(leadantimony)oflargeareawiththinlayersofleadoxide.Such plateshavecomplexdesignswithcircularopeningswherecorrugatedleadribbonsarerolledintospiral ribbons.Thenegativeplatesirrelevantofthetypeofthepositveplatesarebuiltwithpastedplatedesign. Metallicspongeleadisusedonthenegativeplates.Thenegativegridforthemultitubularandplante (positiveplates)ismadeofleadantimony,withthepastedplate,itiseitherleadcalciumorlead antimony.Thegridofalloys,antimonyorcalcium,servesbothpurposesgivesphysicalsupportand strengthtothesoftleadandactsasanelectricconductor.Thegridachievesandretainsaphysicalshape andconductsthecurrenttoallpartsofthematerial.Pastedplateswithleadcalciumalloygridsareused insealedmaintenancefreeleadacidcellsduetothefactthatthistypedoesnotrequirewateringduring itslifetime.Leadantimonyispreferredforinstallationswhereelevatedtemperatureandfrequent cyclingisencountered.Leadcalciumisalsousedforinstallationsrequiringlongerintervalsbetween maintenancewatering.Thedisadvantageofleadcalciumisthatunderfrequentcyclingthelifeofhe batteryisreducedsignificantly. Forthenickelalkalinebatteriestherearetwotypesofplates,thepockettypeandthesinteredtype. Thepockettypeisusedforbothpositiveandnegativeplates.Theactivematerial(nickelhydrate positiveandcadmiumspongenegativeplusadditivestohelpconductivity)issandwichedbetweentwo perforatedstrips(nickelplatedsteel).Thestripsarecrimpedtogetherandthisassemblyisplacedina Ushapeframe.Afterintermeshingthepositiveandnegativetheinsulatorpinsareputinplace,through theframeandplates.Theseelementsarethanputinacontainerandthecellcover(withventcapand appropriateholeforterminalpoles)isinstalled.Therearethreecommonratings:high(discharge shorterthan1hour),mediumrate(dischargeshorterthan4hrs)andlow(thebatterywillsupposedly carryloadsforupto20hrs). Forleadacidbatteries:theelectrolyteisasolutionofdilutedsulphuricacid.Whenthebatteryisfully charged,thepositiveplateisleadperoxideandthenegativeoneisspongelead.Thespecificgravityof theelectrolyteismaximumatstartofdischarge,thereactionbetweentheacidandtheactivematerial producesleadsulphateandwaterthespecificgravitygraduallydecreases.Whenthebatteryisplaced onchargethereversetakesplace.Thevolumeofacidintheelectrolyteofaleadacidbatteryis measuredbyspecificgravity.Specificgravityforstationarybatteriesusedforswgr,controland emergencylightingisapproximately1.210(thehighestvolumeofacidascomparedtoother applicationsbutinlowerconcentration).Todeterminethestateofchargeofthebattery,thegravity readingiscomparedwiththefullchargevaluepublishedandtothespecificgravitydropofaparticular cellsizeataspecificdischargerate.Thereadinghastobecorrectedtotheambienttemperatureattime ofmeasurementifotherthan25degC.FortheNiCad,theelectrolyteisasolutionofpotassium

hydroxidedilutedinwaterwithnormalspecificgravityof1.16to1.19at25degC,additivesareadded toimproveitscapacity.Whenthebatteryisfullychargedthepositiveplatenickelhydrateishighly oxidizedandthenegativeplateisspongemetalliccadmium.Afterdischargetakesplacethepositive platereducestoloweroxidewhilethemetalliccadmiuminthenegativeplateoxidizes.Noneofthe constituentsofthealkalineelectrolytecombinewiththeactivematerialoftheplatesduringchargingor discharging.Thespecificgravityoftheelectrolytecannotbeusedtoindicatethestateofchargeofthe battery.Thespecificgravityreadingswillvaryfromnormalratingwhenheelectrolytetemperatureis lowerorhigherthan25degC,whenthesolutionleveldropsbelowthenormal,orthebatteryhasbeen inserviceforlongtime. Inthisparagraphchargingofbothtypesofbatterieswillbecovered.Theleadacidstationarybatteries arecontinuouslyfloatchargedwhileonastandbystatusandarechargedwithahighconstantpotential currentlimitedlevelafteradischarge.Thehighervoltagevaluedependsontherechargetimerequired torechargethebattery.Asthechargingtimeisshortenedthecharger'scostincreases.Thechargerisa staticrectifier(scr),itsfunctionistochangethesinglephaseorthreephaseinput(120,208,240,480, 600V60HZ)toad.c.outputsuitableforchargingthebatteryandmaintainingaconstantvoltage throughoutthebattery'sloadrange.Topreventtheselfdischargephenomena(standingloss)thecharger maintainsafloatchargethatcontinuouslymonitorsandcorrectsfortheseinternallosses.Batteries equippedwithleadcalciumgridsratherthanleadantimonyrequireafloatchargepercellhigherthan itscounterpart(eg.2.2Vvs.2.15V).Thefullychargedbattery(leadantimonyalloygrid1.210sp. gravity)willdrawbetween.05to0.1Aper100ahofbatteryratedcapacityattheeighthourdischarge rate.Forleadcalciumalloygrid10%to20%ofanidenticalleadantimonyalloywillbedrawn.Current drawnunderdifferentambienttemperatureconditionsisasfollows:thehigherthetemperaturethe higherthecurrentdrawnandviceversa.Chargerscompensate,usually,forvariationsinfloatcurrent demands.Thefloatingcurrentisdirectlyproportionaltothecell(battery)voltage.Thefastertherateof changeinvoltagethehigherhecurrentdrawnatthefloatingvoltage.Thechargershouldbeableto providethefloatingvoltagewithavariationofnomorethanplusorminus1%throughoutitsampere rating. ChargersforNiCadbatteries(stationary)aresimillartotheonesusedforleadacid,floatchargedwhile onstandbyandahigherchargeafteradischarge(foraprolongedperiod)afterwhichfloatchargelevel isresumeduntilfurtherdischarge.Thevalueofthehigherchargingcurrentisatleast5%higherthan the8hourdischargecapacity.FloatrateforNiCadbatteriesisabout1.4to1.45Vpercellat25degC. Afteradischargethehigherchargeisapplieduntilvoltagerisesto1.6percell(itismaintainedfor15to 30hours).Thesizeofthechargerampereratingisusuallymatchedtotheloaddemandplusthe maximumhighchargingraterequiredbythebattery.Thebatterystartstodischargewhenthedemand exceedsthechargersupplyorwhenthea.c.supplytothechargeriscutoff.Thedatarequiredforthe properselectionofachargerare:totalcurrent,voltage(d.c.),duty(continuous,standby,combination), automaticcontrol(recommended),voltage(ac)andnumberofphases.Standardcomponentsthatare foundinachargerare:a.c.&d.c.fuseprotection,d.c.ammeterandvoltmeter,a.c.onpilotlamp, reversebatteryprotection,a.c&d.c.surgeprotection,"highrate"onpilotlight,automaticcurrentlimit shortcircuit,float/highrate/currentlimitpotentiometers,alarmcircuits,highratechargetimer.

Astoragebatteryisconstantlyliveelectricallyandthereforeasourceofelectricalshock.Toolsshould neverbelaidontopofthebatteryassuchanactioncancausesevereshortcircuits.Smokingis forbiddeninbatteryrooms.Hydrogengaslevelshouldneverexceed4%byvolumeinthebatteryroom thusadequateventilationistobeprovided.Refertothelocalelectricalsafetycode(forexampleCSA C22.1)forrequirementsofthemethodofconnectingthebatteriesandofthebatteryroomventilation. Electrolyteusedinleadacidbatteriesishighlycorrosive.Ifspilledonanyobjectithastobe neutralizedthroughtheuseof1lbofbicarbonatesoda&1lbwater.Electrolyteusedwithalkaline batteries,ifspilledhastobeneutralizedbyfloodingthespillwithsolutionofvinegardilutedwith water50/50proportion.Itishighlyrecommendedtousegoggles(orfaceshield)andrubbergloves whenmaintenanceisperformedonabattery. Maintenancetoabatteryistheproperadditionofwater(tapordistilled)tocorrecttheelectrolyte solutionlevelandtokeeparecordsheetwithpertinentinformation.Tapwatercanbeusedifthe impuritylimitsarenotexceeded.Itisimportanttokeepthebatterycleananddry,theconnectorstight, theelectrolyteattheproperlevel,theelectrolytedensityaccordingtothesupplierrecommendations. Nowcoverageofdistributionpanelsandswitchboardswillbepresentedincludingmoldedcasecircuit breakers,safetyswitches,panelboards,multimeteringequipment,groundfaultcircuitinterrupters.Most ofthecodesdefineacircuitbreakerasadevicedesignedtoopenandcloseacircuitautomaticallyata predeterminedovercurrentvalues(shortcircuitoroverload)withoutinjurytoitselfwhenproperly appliedwithinitsrating.Amoldedcasecircuitbreakerirrelevantofthemanufacturercomprisesof: themoldedcase(frame),operatingmechanism,arcextinguishers,contacts,tripelementsandthe terminals(connectorsi.e.mechanical/compressionlugsorsolidbar).Thefunctionofthemoldedcase istoprovideaninsulatedhousingtoassembleandmountallofthecircuitbreakercomponents.The casesaremoldedfromphenolicmaterial.Itprovidesruggednessandhighdielectricstrenghtothe breakerinacompactdesign.Maximumcurrent,voltageandinterruptingcurrentdeterminethesizeand strengthofthemoldedcasecircuitbreaker.Differentmanufacturersbuildbreakersforthesamerating withdifferentphysicalsizesi.e.noninterchangeable.Thefaceplategivesalltheimportantdatasuchas: catalognumber,serialnumberofbreaker,interruptingratingsatdifferentvoltageclasses,standards registrationnumbersi.e.fortheCSAorUL,calibrationtemperatureforthermalmagneticunits,lugs data&size,electricalaccessories,dateofmanufacturing.Thefunctionoftheoperatingmechanismisto provideameansofopeningandclosingthebreaker.Itisofthequickmake,quickbreakmechanism. Thesebreakersarealsotripfreei.e.ifthebreakeroperatinghandleispushedandholdintheon positionandthereisafaultonthesystem(orthetriptestbuttonispushed,ifavailable)thebreaker wouldtripopen&stayopen.TherearethreedistinctpositionsforthehandletosettleintheON,OFF, TRIP(whichismidwaybetweentheONandOFFpositions).Thebreakerhastoberesetaftertripping bypushingthehandleallthewaytotheOFFpositionandthanpushingittotheONposition.The functionofthearcextinguisheristoconfine,divideandextinguishthearcdrawnbetweenthebreaker contactseachtimethebreakerinterrupts.Thetripelementprovidestheprotectionincaseofprolonged overloadsorshortcircuits.Itactuatestheoperatingmechanismandtripthebreakeropen.Thiselement ismadeupofelectromechanicalorsolidstatecomponents.Theelectromechanicalelementisreferred toasthethermalmagneticanditincludes:thebimetallicelementandtheelectomagnet.The

current(load)flowsthroughorheatsthebimetal.Whenacombinationofhighcurrentlevelandalong durationexistswhichissufficienttodeflectthebimetalfarenoughtophysicallypushthetripbarand unlatchthecontacts,thebreakerwilltripopen.Thereisnofieldadjustmentavailableforthethermal element.Themagnetictripactionisachievedthroughtheuseofanelectromagnetconnectedinseries withtheloadcurrent.Whentheshortcircuitcurrentpassesthroughthecoilthiscausesthe electromagnettoattractthearmature(tripbar)andtheunlatchingactioncausesthebreakertotrip open.Magnetictripisadjustablein250Aframebreakerandover.Twoadjustingmethodsareavailable oneistheindependentadjustmentofeachpoleofthebreakerthusthreeadjustingknobsversusone knobtoadjustallpolessimultaneously.Thermalmagnetictripelementsaretemperaturesensitivethus amodifiedunittocompensateforvariationsinambienttemperature(withamodifieddesign)canbe appliedunderspecificconditions.Anambientcompensatedoverloadtripunitcanbeusedwheneverthe breaker(protectingacableoradownstreamdevice)islocatedinadifferentplacewithdifferent ambienttemperaturethantheprotecteddeviceorconductor,thusderatingorupratingofbreakers becomesunnecessary.Ambientcompensationisobtainedbyusinganadditionalcompensatingbimetal whichcounteractstheeffectofambienttemperaturechangesontheoverloadbimetal.Thereare variousmethodsofconnectingthelineandloadsidesofacircuitbreaker:busbars,panelboardstraps, rearconnectedstuds,pluginadapters,terminals(cablelugsforsingleormulticonductorsforcopper onlyorcopper/aluminumones).Thetrippingunitcanbemadeupofsolidstatecomponentsor microprocessorbasedelements.Thesecomponentsreplacethebimetallic&magneticelementsina conventionalmoldedcasec.b.Internalcurrenttransformersinthebreakerarerequiredtofeedinthe S.S.tripunit.Eachframesizecanaccomodateasetofratingplugs,theseplugssettheratedcontinuous currentofthebreaker.Sometypesofratingplugsareadjustablebetween70100%or50100%ofthe ratedcurrentoftheplugitself.Thebreakercharacteristiccurvesaresimilartothethermalmagnetictrip curvesexceptthatthedifferenttrippingactionsaremoreclearlydefinedandcanbeadjusted.The distinctportionsofthech/cscurveare:thelongtimeampererating&thelongtimedelay(simulates

thethermalsectionofathermalmagneticc.b.)theshorttimepickup&theshorttimedelay(I2tinor out),theinstantaneouspickup(simulatesthemagneticportioninathermalmagneticcurve).These breakerscancomewithabuiltingroundfaultprotection(forsolideffectivegroundedneutralonly) withadjustmentofgroundfaultpickupandtimedelay.Thetimecurrentch/cscurvesforcurrent limitingtypec.b.havebasicallythesameshapeasconventionalc.b.Theonlydifferenceisthecurrent limitingactiondisplayedathigherfaultlevels.Atotalinterruptiontimeoffrom1/4to1/2cycleis consistentwiththecurrentlimitingoperation.Theelectromagneticrepulsioncreatedbycloselyspaced parallelcontactarmscarryingcurrentinoppositedirectionsintensifiedbyanOshapedmagnet surroundingthecontactarmcausesthecontactstoblowopeninanextremelyshortperiodoftime. Circuitswhichproducehighfaultcurrentstypicallyareassociatedwithlowshortcircuitpowerfactors (i.e.highX/Rratios).Thehighspeedcontactseparationenhancestheabilityofthec.b.tolimitboththe peakcurrentandtheletthroughenergy.Theintegralcurrentlimitingbreakerissimilartothestandard thermalmagneticexceptthatitincorporatesacurrentlimitingdevice.Thisdeviceconsistsof3current limitersspeciallydesignedtocoordinatewiththebreakerofwhichtheyareanintegralpart.All normaloverloadsands.c.faultsareinterruptedbythethermalmagneticportionofthec.b.Whena

largefaultoccursthetriggertypecurrentlimiterswillblowandoperatethetripbartoopenthebreaker, thuspreventingsinglephasing. Thestandardmoldedcaseswitch,whichisamorecompactdesignthantheconventionaldisconnect switch,hasnotripunit.Itconsistsofthestandardbreakercontacts,bussingandlugsforthehighest ampereratingineachframesizeandismanuallyoperatedonly. Thesafetyswitchescanbesinglethrowordoublethrow.Allswitchestohavevisiblebladesandsafety handles(interlockbypasslever,crossbarandoperatingspring).Therearetwotypesofswitchcontacts thebuttandtheknifeblade/jawconstruction.Intheformer,onlyoneofthebladescontactsurfaceis heldintensionagainsttheconductingpath,electromagneticforcesduetohighcurrentfaultswilltend toforcethecontactsapartthereforearcingandcontactburningmaybetheresult.Inthelatterthejaws distributeauniformclampingpressureonbothsidesofthebladecontactsurfaces,theelectromagnetic forcesduetothehighs.c.currentswilltendtosqueezethe2sidesofthejawtogetherontotheblade. Theactionoftheblademovinginandoutofthejawsaidsincleaningthecontactsurfaces.The contactsaremadeofcopperandthecurrentcarryingpartsoftheswitchareplated,toreduceheating. Fusedswitcheswillhavefuseclips/holdersplatedandeitherspringreinforcedornot,theclassesfound ontheseswitchesareJ,R,orLfor800Aandover.Themoldedcaseswitchesandthesafetyswitches areinstalledinavarietyofenclosurestomeetpracticallyallapplications.Theenclosuresare designatedaccordingtoNemastandards(1,3R,4,4X,5,...etc.)orCSA(1,2,3,..etc)alltheenclosureshave togothroughasetofqualifyingtestsbeforebeengivensuchadesignation. Now,weshallcoverpanelboards.Thesetypesofboardscanbeclassified,broadly,intotwocategories: lightinganddistribution/power.Anothermethodofclassificationiswhethertheboardcontains breakers,switches(fusedorunfused)oracombinationthereof.Thepanelboardscanalsobeclassified accordingtothemain,acceptingtheincomingcable,whetheritisabreakeraswitchorjustasetof lugs.Theratingranges,forsinglephase(threewire)orthreephase(threeorfourwire)lightingpanels, from120/240Vto600V50A800Amainbreakerormainlug.Theratingsrangeforsinglephase(two orthreewire)orthreephase(threeorfourwire)powerpanelsfrom120/240Vthrough600Va.cor 250Vd.c.,mainbreakerorswitchorlugs,upto1200A.Themajorcomponentsofthebreaker panelboardsaretheboxwhichcomesinstandarddimensions,theinteriorwhichholdsthebreakers andcomesinstandardcurrentcarryingcapacity&mountingspaces,thesolidneutralwhichisabare conductingbarwithlugs,thetrimeitherflushorsurfacewhichcoverstheguttersandhasthedoor thatcoversthebranch/mainbreakers,finallythebreakersplugonorboltedtype.Forthefusible panelsthecomponentsare:thefusibleswitchunit,theinteriorassembly,theenclosuretheboxandthe fronttrimparts,thecoverplates(blanks)andtheneutral. Therearemeteringequipment(centresorsockets)thatareusedforsinglephaseandthreephase systems.TheyareunitsthatactasthepointofplacementfortheP.U.toplaceitsdetachablemeter (watthour).Thesinglephase120/240V,3wireunitsareusedinconjunctionwiththeloadcentrewhich islocatedinsidethesinglefamilyresident.Therearethreetypesofmetersockets:thenoncircuit closing,automaticcircuitclosingandthemanualcircuitclosing.Thefirstmeanswhenthewatthour meterisremovedtheservicetothedownstreamloadisinterrupted,thesecondmeansthata mechanismtoshortthelinetotheloadjawsofthesocketwhenthemeterisdetachedisprovided,the

thirdofferstheabilityofshortingthelinetotheloadjawsofthesocketmanuallythroughtheuseofa sliderorleverbeforeremovingthemeter.Allthesemechanismsaremeantfortemporarilyshortingthe socketandusuallyrated50%ofthecontinuouscurrentcarryingcapacityofthesocket.Thejumperbars arenottobeusedtomake/breakcurrent.The4jawmetersocketisusedon120/240Va.c.,1phase,3 wire.The5jawusedwithsinglephaseloadsfedfrom3phase,4w120/208Vacsystem.For3phase,4 wiresystemsthe7jawmetersocketisusedwiththepropermetertomeasuretheenergyconsumption oftheconnectedloads.Thetypeofsockettrimwillsuitthetypeofsocketinstalled.Thesemeter socketscanbeassembledtogetherinonelineuptometerdifferentloadsinonelocationlikeshopping centers,apartmentbuildings,...etc.Theyarebuiltforindoororoutdoorinstallations. Inthisparagraphpeopleprotectionratherthanequipmentprotectionfromgroundfaultswillbe discussed.Thedeviceusedisknownasgroundfaultinterrupter(GFI).Thehandtohandresistanceof anadultliesbetween1000to4000ohmsfunctionofvoltage,moisturelevelsandmuscularstructure. Theeffectofa60c/sshockonanormaladultareasfollows:over5mapainfulshock,over15mais sufficienttocausefreezing,over30macausesdifficultyinbreathingthatcanleadtosuffocation,50 100mapossibleventricularfibrillation,100200madefiniteventricularfibrillation,over200masevere burns&musclecontractions.Astandardovercurrentdevicewillneversensesuchlowlevelsofcurrent despitethefactthatitisdangeroustothehumanbeing.Groundfaultcircuitinterruptersarecoveredin theULstandard943andtheCSAC22.2no.144.TheGFIshouldtripwhenthegroundcurrentreaches

6maormore,thetimeitshouldtaketotrip=[20/groundfaultcurrent]1.43.Thisdeviceshouldnottrip below4ma,italsocontainsameansoftestingthegroundfaultcircuitry.ThestandardsclassifytheGFI intoclassA(whichisbrieflycoveredabove),portableandnonclassifiedones.TheGFIsensing componentsarethezerosequencecurrentsensorthatmonitorsthebalanceofthecurrentineitherthe singlephase2wirecircuit(thehotandneutralwires)orthesinglephase3wirei.e.2polebreakers(the 2hotandtheneutralwires).Whenthesensordetectsanunbalance,aslowas6ma,itwillsendasignal tothecontrolcircuitry.Thiswillinitiateatripofthebreakerfeedingthefaultycircuit(havingthe leakagecurrenttoground).TherulesthatgoverntheapplicationanduseoftheGFIaregiveninthe localapplicablecode,eg.CSAC22.1.