2014 NatioNal REFERENCE GUIDE - Control Design Transformer Protection ... National Electrical Code...
Transcript of 2014 NatioNal REFERENCE GUIDE - Control Design Transformer Protection ... National Electrical Code...
REF
EREN
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GU
IDE
2014 NatioNal ElEctrical codE®
Changes in Overcurrent and Surge Protection
2 Mersen • NEC Code 2014
Selected 2014 NEC Code Changes in Overcurrent and Surge ProtectionContents
1. New Circuit Breaker Requirements for 1200A Plus Circuits . . . . . . . . . . . . . 3 240.87Arcflashenergyreductionmandated
2. Surge Protective Device Type 4 and New Requirement . . . . . . . . . . . . . . . . . 4 285.13Type4ComponentSPDs 700.8
3. Surge Protection Without Overcurrent Protection . . . . . . . . . . . . . . . . . . . . . 6 240.21(C)(2)1bexception
4. Short-Circuit Current Rating (SCCR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 409.1Panelsnowincludeupto1000volts
5. Solid State Motor Circuit Protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 430.52C(5) 430.130 430.131
6. Ground Fault Protection (GFP) for 1000A Plus Circuits. . . . . . . . . . . . . . . . 12 210.13Newrequirementsandexceptions
7. Sizing Transformer Protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 Table450.3(A) Table450.3(B)
8. PV Shut-off for First Responders. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 690.12
9. Selective Coordination Requirements. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 620.62 700.28EmergencySystems 701.27LegallyrequiredStandbySystems 708.54
10. Selective Coordination Not Required in Hospitals . . . . . . . . . . . . . . . . . . . . 18 517.2CriticalbranchDefinition 517.30(G)Coordination
NationalElectricalCode®andN.E.C.®areregisteredtrademarksoftheNationalFireProtectionAssociation(NFPA),Quincy,MA02269.ThispublicationdoesnotreflecttheofficialpositionoftheNFPA.
TherecommendationsbyMerseninthispublicationareintendedtobeincompliancewiththe2014NEC,howeverjurisdictionsthatadoptthecodearesolelyresponsibleforanymodificationsandinterpretationstobeenforcedbytheirjurisdictions.
TheuserofthecodeshouldidentifywhatregulatoryauthorityhasresponsibilityfortheinstallationapprovalandalwayscomplywithanyregulatoryauthoritymodificationstotheN.E.C.Mersencannotberesponsibleforerrorsandomissions.
Mersen • NEC Code 2014 3
1. New Arc Flash Circuit Breaker Requirements for 1200A or morePrevious Code requirements
Forthefirsttimeinthe2011code,arcflashdangerfromcircuitssuppliedbycertaintypesofcircuitbreakerswasrecognized.Circuitbreakerswithoutaninstantaneoustripwererequiredtouseanadditionalmethodforreducinganarcflashdanger.
TheSection240.87Non-instantaneousTripinthe2011codesaid,“Whereacircuitbreakerisutilizedwithoutaninstantaneoustrip,oneofthefollowingorapprovedequivalentmeansshallbeprovided:
1. Zone-selectiveinterlocking2. Differentialrelaying3. Energy-reducingmaintenanceswitchingwithlocalstatusindicator.”
Thesealternativesareeffective,butcostly.
new Code
240.87 Arc Energy Reduction. Wherethehighestcontinuouscurrenttripsettingforwhichtheactualovercurrentdeviceinstalledinacircuitbreakerisratedorcanbeadjustedis1200Aorhigher,240.87(A)and(B)shallapply.
(A) Documentation. Documentationshallbeavailabletothoseauthorizedtodesign,install,operate,orinspecttheinstallationastothelocationofthecircuitbreaker(s).
(B) Method to Reduce Clearing Time. Oneofthefollowingorapprovedequivalentmeansshallbeprovided: (1)Zone-selectiveinterlocking (2)Differentialrelaying (3)Energy-reducingmaintenanceswitchingwithlocalstatusindicator (4)Energy-reducingactivearcflashmitigationsystem (5)Anapprovedequivalentmeans
Informational Note No. 1: Anenergy-reducingmaintenanceswitchallowsaworkertosetacircuitbreakertripunitto“nointentionaldelay”toreducetheclearingtimewhiletheworkerisworkingwithinanarc-flashboundaryasdefinedinNFPA 70E-2012, Standard for Electrical Safety in the Workplace,andthentosetthetripunitbacktoanormalsettingafterthepotentiallyhazardousworkiscomplete.
Informational Note No. 2: Anenergy-reducingactivearcflashmitigationsystemhelpsinreducingarcingdurationintheelectricaldistributionsystem.NochangeinthecircuitbreakerorthesettingsofotherdevicesisrequiredduringmaintenancewhenaworkerisworkingwithinanarcflashboundaryasdefinedinNFPA 70E-2012, Standard for Electrical Safety in the Workplace.
4 Mersen • NEC Code 2014
1. New Arc Flash Circuit Breaker Requirements for 1200A or more, Continuedreasons for Changes
Manysystemswerecompletelydesignedusingonlyinstantaneoustripcircuitbreakers.Thatcompliedwiththecode,butwasnotmakinguseofavailablesafertechnology.
Thenewcoderequiressafertechnologytobeusedforanycircuitusingacircuitbreakerthatcanbesetat1200ampsormore.Thisdoesnotapplytocircuitswithfuses1200ampsorlarger.
how to ComPly
Everylargecircuitismorelikelytohavehigher,morehazardouslevelsofarcflashdanger.Selectaneffectivedesignoptionthatisthemostcost-effectiveforthelargecircuits.Zone-selectiveinterlockingrequiresupstreamcircuitbreakerstohaveacommunicationschanneltothedownstreamunit.Differentialrelayingcanbecomplexforcommissioninganduse.Energyreducingmaintenanceswitchesandactivearcflashcontroloftenrequireexpensivesolid-statetripcircuitbreakers.Electricalinspectorsseldomapproveothermethodsbecauseoftheirpotentialliability.Apossiblecost-effectivesolutionistodesigninfusibleprotectioninsteadofcircuitbreakers.
helPful ProduCts
TheAmp-Trap2000®familydeliverscurrentlimitingfusesthatcanreducecostsandreducearcflashdangertoaminimumwhentheavailablefaultcurrentisadequate.Thisisfrequentlymoreeconomicalthatothersolutions.
TheAmp-Trap2000ClassL1200ampfusecanlimitthearcflashdanger.Forexample,theMersenA4BQ1200fusewithavailableboltedfaultcurrentat24,000ampsat600volts,willlimitthearcflashincidentenergyto3.8cal/cm2ata24inchworkingdistance.InthisexamplethefusereducesthePPErequireddowntoHazardRiskCategory1.Inhigheravailablefaultcurrentapplications,itcanreducethehazarddowntoHRC0.
2. Surge Protective Device (SPD) Type 4Previous Code requirements
Article285hadthetransitionalphrasingfrom2005tointroducethenewtermSPDandstillusetheoldtermTVSS.ULStandard1449Revision3wassubstantiallyrevisedsothatthenamewaschangedtoemphasizethemajordifferencebetweenthesafetyofaTVSSandanSPD.
TherequirementsforapplyingSPDTypes1,2,and3weredocumented.SPDType1canbeusedanywhereinthecircuitbecauseitisself-protectingwithinitsrating.Type2unitsneedupstreamprotectionsuchastheserviceentrance.TheType3unitsaretobeusedmorethan30feetawayfromtheserviceentrance.ThecodeexplainedtheapplicationforTypes1,2and3SPDs,butwassilentonType4.
ThepriorcodedidnotrequireSPDs,butthroughtheyearstheelectricalindustrydeterminedthattheywereeffectiveinpreventingdamagetoelectroniccircuitsfromvoltagespikesandsurges.ManySPDshavebeenvoluntarilyappliedwithoutanycoderequirements.Aselectronicequipmentbecomesmorecommononallcircuits,thepotentialdamageanddowntimeofcriticalcircuitswasbecomingapparent.
Mersen • NEC Code 2014 5
2. Surge Protective Device (SPD) Type 4, Continued
new Code
285.13 Type 4 and Other Component Type SPDs. Type4componentassembliesandothercomponenttypeSPDsshallonlybeinstalledbytheequipmentmanufacturer.
700.8 Surge Protection. AlistedSPDshallbeinstalledinoronallemergencysystemsswitchboardsandpanelboards.
reasons for Changes
ThetermTVSSwaseditedoutofArticle285.ThecommitteedecidedthattherehadbeensufficienttimefortheindustrytoadjusttotheSPDterm.
SomepeopleweremisapplyingType4SPDs.Paragraph285.13wasaddedtopreventpeoplefromapplyingType4SPDsinthefield.
Type4SPDsdonothavecompliancewithsomeofthesafetyfeaturesmandatedbyType1,2,or3SPDs.Theyareintendedtobeselectedbyapanelshopthathasthecapabilityofchoosingtheappropriatecharacteristics.Type4unitsareoftenDIN-railmountandhaveexposedliveterminals.Thesearesuitableformountingintoanenclosure,butnotintheopen.
Newparagraph700.8requiressurgeprotection.Article700pertainstoemergencysystems,whicharesystemslegallyrequiredtoautomaticallysupplypowertodesignatedloadsuponlossofnormalpower.Thiscanpreventdamageofemergencypowercontrolsanddamagetocriticalelectronicloads.
how to ComPly
UseonlyType1,2,and3SPDsforgeneralfieldaddition.Theyaredesignedtosafelymitigateharmfulsurgesandvoltagespikes.TheType4unitsshouldbecarefullychosenfortheapplication.Sometimesapplyingthemintoanenclosureisadequate.Sometimestheyhavespecificupstreamprotectionneeds.AqualifiedpersonhastoanalyzetheSPDlimitationsinordertoproperlyapplyType4units.
NewormodifiedemergencysystemsshouldhaveSPDsintheirswitchboardsandpanelboards.ThisisthefirstcoderequirementformandatoryuseofSPDs.
helPful ProduCts
MersenhasalargearrayofSurgeProtectiveDevices.InadditiontotheType1and2generalapplicationproducts,MersenhasalargevarietyofType4units.
MersenType4unitsareappliedtogeneralcontrolpanels,PVsystems,windturbines,andpowerelectronics.Type4unitscanbemodularorpluggable,ACorDC,andULorIECrated.
6 Mersen • NEC Code 2014
3. Surge Protection Without Overcurrent ProtectionPrevious Code requirements
Section240.1requiredovercurrentprotectiontobelocatedatthepointwheretheconductorsreceivetheirsupplywitheightexceptions.Thissectioniscommonlycalledthe“TapRules.”ThepriorcodedidnotreferenceanyexceptionsforinstallingType1SPDsthatareselfprotected.
Paragraph285.23(A)(1)gavepermissiontowireType1SPDsbeforeoraftertheserviceentrance.Thisparagraphreferredto230.82(4)asgivingpermissiontoinstalltheseunitsonthesupplysideoftheservicedisconnectingmeans.
new Code
240.21(B) Feeder Taps. Conductorsshallbepermittedtobetapped,withoutovercurrentprotectionatthetap,toafeederasspecifiedin240.21(B)(1)through(B)(5).Theprovisionsof240.4(B)shallnotbepermittedfortapconductors.1. Taps Not over 3m (10 ft) Long. Ifthelengthofthetapconductorsdoesnotexceed3m(10ft)andthetapconductorscomplywithallofthefollowing:
(1)Theampacityofthetapconductorsis
a.Notlessthanthecombinedcalculatedloadsonthecircuitssuppliedbythetapconductors,and
b.Notlessthantheratingoftheequipmentcontaininganovercurrentdevice(s)suppliedbythetapconductorsornotlessthantheratingoftheovercurrentprotectivedeviceattheterminationofthetapconductors.
Exception to b: Where listed equipment, such as a surge protective device(s) [SPD(s)], is provided with specific instructions on minimum conductor sizing, the ampacity of the tap conductors supplying that equipment shall be permitted to be determined based on the manufacturer’s instructions.
240.21(C) Transformer Secondary Conductors. Asetofconductorsfeedingasingleload,oreachsetofconductorsfeedingseparateloads,shallbepermittedtobeconnectedtoatransformersecondary,withoutovercurrentprotectionatthesecondary,asspecifiedin240.21(C)(1)through(C)(6).
Exception to (C)(2)(1)b: Where listed equipment, such as a surge protective device(s) [SPD(s)], is provided with specific instructions on minimum conductor sizing, the ampacity of the tap conductors supplying that equipment shall be permitted to be determined based on the manufacturer’s instructions.
Mersen • NEC Code 2014 7
3. Surge Protection Without Overcurrent Protection, Continuedreasons for Changes
ItwasunclearifType1SPDsshouldhaveovercurrentprotectionintheirsupplysidecircuitornot.TheoldcodeconsideredtheType1unitstobeself-protected,butwasthewiretobeconsideredasprotected?Ifwirewasconsideredprotected,howsmallcoulditbe?
ManySPDmanufacturersmanagedthisbyrecommendingadditionalovercurrentprotectionsizedforthewiresupplyingtheSPD.Butiftheovercurrentprotectionwasnotused,manyelectricalinspectorswouldnotapprovetheinstallation.
how to ComPly
ThenewcodehasexceptionsallowingSPDsandotherlistedequipmenttobeinstalledwithoutadditionalovercurrentprotection.Thisnewexceptionpertainstofeedertapsandtransformersecondarytapswithdistancesnotexceeding10feet.
SelectlistedSPDswithmanufacturerinstructionsthatincludeminimumwiresizing.Thiswiresizingandinstallationhavetocomplywiththeotherpreviousrequirementsforthe10footTapRule.
helPful ProduCts
MersenhaslistedSPDsformostapplications.TheMersenmodelsaredesignedtoprotectserviceentrances,panels,andend-useequipment.
8 Mersen • NEC Code 2014
Previous Code requirements
Forthefirsttimeinthe2005code,industrialcontrolmachineryandpanels,airconditioningequipment,refrigerationequipment,meterdisconnectswitches,andmotorcontrollershadtobemarkedwiththeirSCCR(Short-CircuitCurrentRating).
The2008codedefinedSCCRas,“Theprospectivesymmetricalfaultcurrentatanominalvoltagetowhichanapparatusorsystemisabletobeconnectedwithoutsustainingdamageexceedingdefinedacceptancecriteria.”SeveralcodesectionshavespecificlabelingrequirementssuchasinSection409forIndustrialControlPanelsandSection670forIndustrialMachinery.
The2011coderequiredin409.22andalsoin670.5-Anindustrialpanelshallnotbeinstalledwheretheavailablefaultcurrentexceedsitsmarkedshort-circuitcurrentrating.Thismadeitaclearcodeviolationtoinstallanindustrialcontrolpanelrated600voltsorlesswithalowerSCCRratingthantheavailableshortcircuitcurrent.
Alsothe2011codecontainedaprovisionin110.24requiringfieldmarkingofnewserviceentranceequipmentwiththeavailableshortcircuitcurrent.ThatmadeiteasierforelectricalinspectorstocompareandquestiontheSCCRratings.
new Code
ARTICLE 409: Industrial Control Panels
I.General
409.1Scope.Thisarticlecoversindustrialcontrolpanelsintendedforgeneraluseandoperatingat1000voltsorless.
reasons for Changes
TheNationalElectricalCodewasoriginallyfocusedon600voltequipment.The2014codechangedthefocustoequipmentupto1000voltequipment.ThisincreasesthenumberofpanelsrequiredtohaveSCCRratingsandcompliance.Forexample,a750voltsolarinverterpanelnowhastocomply.
ThecodeagainisemphasizingSCCRlabelingandinstallationrequirements.HistoricallymanufacturersbeganlabelingelectricalequipmentwiththeSCCR,butmanypeoplefailedtorealizeitssignificance.Somepeoplejustassumeditwasunimportantlabeling.Thecodemandatedthelabeling,butthepriorcodeswereunclearhowtousethisinformationuntil2011.
Somepanelbuyersonlycheckedforthelabel,andthatthemanufacturersprovidedit.ButtheequipmentcouldbeatdangerouslylowSCCRlevelsfortheapplication.ThepanelusersneededmoredescriptiononhowtousetheSCCRlabelinformation,whichwasonlygivenin2011.
4. Short Circuit Current Ratings for 1000V
Mersen • NEC Code 2014 9
4. Short Circuit Current Ratings for 1000V, Continuedhow to ComPly
Thenewrequirementexpandsthecontrolpanelscoveredbythisrequirementfrom600voltsupto1000volts.
IndustrialcontrolandmachinepanelshavetobemarkedwiththeirSCCR.ThemanufacturersordesignersofthepanelmustdoananalysisasdescribedinUL508A,evenifthepanelisnotbuilttotheUL508AStandardspecifications.
Thentheinstallermustinsurethatthepanel’sSCCRisnotlessthantheavailablefaultatthesupplyterminalsofthepanel.FinallytheelectricalinspectorhastoverifythattheSCCRisonthenameplateandhavesomeevidencethattheSCCRisnotexceeded.
Compliancecanbecostlyifthepersonwhoisresponsibleforcodecomplianceignoresthiscodeissueuntiltheequipmentisinstalled.Extensivetimecanbeconsumedinnegotiatingwhoshouldpayfortheproblemresolution.Theinstallationfixoftenrequiresreturnofthepaneltothemanufacturerforupgrading.
helPful ProduCts
TheAmp-Trap2000®familydeliverscurrent-limitingfusesthatcanincreasetheSCCRofindustrialcontrolpanels.ProductssuchastheUltraSafeTMUSFMfuseholderdirectlyreplacecircuitbreakershavingthesamewidthastypeIECstarters.TheSurge-Trap®productsprotectagainstvoltagespikesandhaveabuilt-inratingofupto200kASCCR.Thefinger-safepowerdistributionblockscanalsohavea100kAratingwithfuses.
10 Mersen • NEC Code 2014
5. Solid-State Motor Protection with FusesPrevious Code requirements
Theformer430.52textusedthephrasing“Suitablefuses,”insteadofsemiconductorfuses.ItgavepermissiontosubstitutesuitablefusesfortherequirementsofTable430.52aslongastheequipmentwasmarkedtoidentifysuitablereplacementfuses.
SectionXAdjustable-Speed Drive SystemsofArticle430Motors,Motor Circuits and Controllershadnoinformationonshortcircuitandgroundfaultprotectiverequirements.Thatmeantthenon-adjustablespeeddrivecodesectionsprobablyapplied.
new Code
430.52 Rating or Setting for Individual Motor Circuit.
(C) (5) Power Electronic Devices. SemiconductorfusesintendedfortheprotectionofelectronicdevicesshallbepermittedinlieuofdeviceslistedinTable430.52forpowerelectronicdevices,associatedelectromechanicaldevices(suchasbypasscontactorsandisolationcontactors),andconductorsinasolid-statemotorcontrollersystem,providedthatthemarkingforreplacementfusesisprovidedadjacenttothefuses.
430.130 Branch-Circuit Short-Circuit and Ground-Fault Protection for Single Motor Circuits Containing Power Conversion Equipment.
(A) Circuits Containing Power Conversion Equipment. Circuitscontainingpowerconversionequipmentshallbeprotectedbyabranch-circuitshort-circuitandground-faultprotectivedeviceinaccordancewiththefollowing:
(1)Theratingandtypeofprotectionshallbedeterminedby430.52(C)(1),(C)(3),(C)(5),or(C)(6),usingthefull-loadcurrentratingofthemotorloadasdeterminedby430.6.
(2)Wheremaximumbranch-circuitshort-circuitandground-faultprotectiveratingsarestipulatedforspecificdevicetypesinthemanufacturer’sinstructionsforthepowerconversionequipmentorareotherwisemarkedontheequipment,theyshallnotbeexceededevenifhighervaluesarepermittedby430.130(A)(1).
(3)Aself-protectedcombinationcontrollershallonlybepermittedwherespecificallyidentifiedinthemanufacturer’sinstructionsforthepowerconversionequipmentorifotherwisemarkedontheequipment.
InformationalNote:Thetypeofprotectivedevice,itsrating,anditssettingareoftenmarkedonorprovidedwiththepowerconversionequipment.
(B) Bypass Circuit/Device. Branch-circuitshort-circuitandground-faultprotectionshallalsobeprovidedforabypasscircuit/device(s).Whereasinglebranch-circuitshort-circuitandground-faultprotectivedeviceisprovidedforcircuitscontainingbothpowerconversionequipmentandabypasscircuit,thebranch-circuitprotectivedevicetypeanditsratingorsettingshallbeinaccordancewiththosedeterminedforthepowerconversionequipmentandforthebypasscircuit/device(s)equipment.
430.131 Several Motors or Loads on One Branch Circuit Including Power Conversion Equipment. Forinstallationsmeetingalltherequirementsof430.53thatincludeoneormorepowerconverters,thebranch-circuitshort-circuitandground-faultprotectivefusesorinversetimecircuitbreakersshallbeofatypeandratingorsettingpermittedforusewiththepowerconversionequipmentusingthefull-loadcurrentratingoftheconnectedmotorloadinaccordancewith430.53.Forthepurposesof430.53and430.131,powerconversionequipmentshallbeconsideredtobeamotorcontroller.
Mersen • NEC Code 2014 11
reasons for Changes
Theprior430.52textdidnotexplainwhatwasasuitablefuse.Thatmadetherequirementdifficulttomeetorenforce.Semiconductorfusesareveryfastactingcurrent-limitingfuses.TheULStandard248-13doesnotrequireoverloadprotectioninthesefuses.Typicalbranch-circuitratedfusesdocontainoverloadprotection.Somefusesaremorecurrent-limitingandgivebettershort-circuitandground-faultprotection.
Thesameselectionconcernsarepresentforbothpowerelectronicdevicesandpowerconversionequipment.Nowclearlysemiconductorfusescanbeusedforprotection.Iftheyareused,thefuseholderareamustbeclearlymarkedwhichfuseshouldbeusedforprotectingpowerconversionequipment.
how to ComPly
Powerconversionequipmentshouldbecoordinatedwiththemanufacturer’sinstructions.Ifthemanufacturersaysfuses,itcannotbeprotectedbycircuitbreakers.Forexample,ifthepowerconversionequipmentmanufacturerstatesamaximumampereofaULClassJfuse,thatbecomesacoderequirement.
helPful ProduCts
Mersenisthelargestsupplierofsemiconductorfusesintheworld.Semiconductorfusesareproducedinawidevarietyofshapes,sizesandratings.
5. Solid-State Motor Protection with Fuses, Continued
12 Mersen • NEC Code 2014
6. Ground Fault Protection (GFP) for 1000A BranchesPrevious Code requirements
GFPisfortheprotectionofequipment.SometimesthisrequirementisconfusedwithGFCI,whichistoprotectpeoplefromshock.GFCIsarelookingformilliampsofcurrent.TheGFPcanbesettoignoregroundfaultsbelow1200ampsandcanhavetime-delayofonesecondforcurrentsof3,000ampsorabove.Thedetailsareinsection230.95.
PriorcodemandatedGFPforsomeservicesandfeeders.Howeverifalargebranchcircuitfitthesamedescription,itwasnotrequiredtohaveaGFP.
new Code
210.13 Ground-Fault Protection of Equipment. Eachbranch-circuitdisconnectrated1000Aormoreandinstalledonsolidlygroundedwyeelectricalsystemsofmorethan150voltstoground,butnotexceeding600voltsphase-to-phase,shallbeprovidedwithground-faultprotectionofequipmentinaccordancewiththeprovisionsof230.95.
InformationalNote:Forbuildingsthatcontainhealthcareoccupancies,seetherequirementsof517.17.
Exception No. 1: The provisions of this section shall not apply to a disconnecting means for a continuous industrial process where a non-orderly shutdown will introduce additional or increased hazards.
Exception No. 2: The provisions of this section shall not apply if ground-fault protection of equipment is provided on the supply side of the branch circuit and on the load side of any transformer supplying the branch circuit.
reasons for Changes
TheoriginalrequirementsforGFPinservicesandfeedersweretheresultofequipmentburn-downs.Althoughbranchcircuitsthislargeareuncommon,theyexistandsomeburn-downshaveoccurred.Thenewrequirementisintendedtopreventfutureburn-downsinlargebranchcircuitsofgrounded480voltsystems.
how to ComPly
ApplyGFPtobranchcircuitsof480groundedsystemswhentheovercurrentprotectionis1000ampsormore.
helPful ProduCts
MersenA4BQAmp-Trap2000fusesarefasteractingthanregularClassLfuses.Theycangivebetterprotectionevenifaburn-downstarts.
Mersen • NEC Code 2014 13
7. Sizing Transformer ProtectionPrevious Code requirements
Transformerprotectionrequirementsaredividedintotwotables,oneforlowervoltagesandtheotheroneforhighervoltages.Thepriorcodeused600voltsasthethresholdbetweenthetwotables,450.3(A)and(B).
Thesetablesusedifferentcriteriaformaximumovercurrentprotection.Table450.3(A)considerstheimpedanceofthetransformer,and450.3(B)considersfullloadcurrents.Thereweredifferentrulesdependinguponwhetherthevoltagewasover600voltsornot.
new Code
Table 450.3(A) MaximumRatingorSettingofOvercurrentProtectionforTransformersOver1000Volts(asaPercentageofTransformer-RatedCurrent)
Table 450.3(B) MaximumRatingorSettingofOvercurrentProtectionforTransformers1000VoltsandLess(asaPercentageofTransformer-RatedCurrent)
reasons for Changes
TheNationalElectricalCodewaschangedinitsentiretytomoregenerallyapplytocircuitsupto1,000voltsinsteadof600volts.Manyrevisions,mostlyeditorial,weremadetothe2014code.Whensomanyrevisionsaremadeatonetime,sometimesunintendedconsequencesresult.
how to ComPly
Usethetablestoselectthemaximumovercurrentprotectionallowed.Mosttransformerapplicationswillnotchange.Anytransformerapplicationsover600voltsbutnotover1,000voltscouldhavedifferentrequirements.
Manyhigherratedvoltagetransformerfuseselectionscouldbeimproved.Historicallyengineerssizedtheprimaryfusestothemaximumallowedbycodetoavoidnuisanceopenings.Inrecentyearspeoplebecamemoreknowledgeableaboutthedangersofarcflashandtheeffectsofsizingovercurrentprotection.
Transformerfuseapplicationlessthanthemaximumsize,butstilllargeenoughtopreventnuisanceopening,canreducearcflashhazards.Arcflashincidentenergyisproportionaltothedurationofthearcflash.Asmallerampereratedfusewilloperatefasterwiththesameamountofarcfaultcurrent.Evenselectingamoreinverse,lesstime-delayfuse,canreducearcflashenergyusingthesameampererating.
helPful ProduCts
Mersenhasthewidestrangeofcurrent-limitingmediumvoltagefusesfortransformersthatmeettheNorthAmericanANSI/IEEEstandards.TheHMHmodelofmediumvoltagefusescanreduceincidentenergyonthesecondarysideofthetransformerbybeinginstalledintheprimary.Somemediumvoltagefusescanreducearcflashincidentenergytotolerablelevelsusingexistingfusiblegear.
14 Mersen • NEC Code 2014
8. Solar System Shut-Down for First RespondersPrevious Code requirements
TherewerenopreviousrequirementsforrapidpowershutdownonrooftopPVsystems.Thereonlywerenormalshutdownsystemsincorporatingdisconnects,inverters,andelectronicallycontrolledequipment.
new Code
690.12 Rapid Shutdown of PV Systems on Buildings. PVsystemcircuitsinstalledonorinbuildingsshallincludearapidshutdownfunctionthatcontrolsspecificconductorsinaccordancewith690.12(1)through(5)asfollows.
(1)RequirementsforcontrolledconductorsshallapplyonlytoPVsystemconductorsofmorethan1.5m(5ft)inlengthinsideabuilding,ormorethan3m(10ft)fromaPVarray.
(2)Controlledconductorsshallbelimitedtonotmorethan30voltsand240volt-ampereswithin10secondsofrapidshutdowninitiation.
(3)Voltageandpowershallbemeasuredbetweenanytwoconductorsandbetweenanyconductorandground.
(4)Therapidshutdowninitiationmethodsshallbelabeledinaccordancewith690.56(B).
(5)Equipmentthatperformstherapidshutdownshallbelistedandidentified.
Mersen • NEC Code 2014 15
8. Solar System Shut-Down for First Responders, Continuedreasons for Changes
Emergencyresponders,suchasfirefighters,areexposedtodangerousvoltagesfromPVsystemsiftheyareworkingonaroofwithsmokeobstructedview.Thenormalfirefighterproceduresofsuppression,ventilation,andoverhaulentailworkingontheroof.IftheroofhasPVsystemspresent,itcomplicatesaccessandpresentsdangerousshockhazards.
EuropehasextensiveexperiencewiththeirPVsystemsandhasdevelopedsomerapidshutdownsystems.ThenewcodesectionwasdevelopedafterreviewingtherelatedportionofIEC61730,PVModuleSafetyQualification.
how to ComPly
Installarapidshutdownsystemthatwillbringthesystemdownto30voltsorlesswithin10secondsofinitiation.Thecoderequiresthattherapidshutdownsystembealistedproduct.Alistedunitmeetsthekeycriteriaandisalreadyevaluatedforeasycompliance.
helPful ProduCts
Mersen’sPVSafetySystemhasbeenprovidinganIECrapidPVshutdowncapabilityinEuropeforsometime.ShortlythatunitwillbemodifiedandULlistedfortheAmericas.
MersenhasawiderangeofotherPVproducts.Thetraditionalproductsincludefuses,fuseblocks,powerdistributionblocks,disconnectswitches,surgeprotectivedevices,coolingproducts,andlaminatedbusbarsolutions.
RecentlyMersenintroducedamodularPVdatacollectionsystem.ThissystemcollectsimportantdatafromPVstrings,combinerboxes,andotherfieldinstruments,andthensendsthisdataoveraRS485communicationslink.
16 Mersen • NEC Code 2014
9. Selective Coordination RequirementsPrevious Code requirements
Thepreviouscodedefinedselectivecoordinationas,“Localizationofanovercurrentconditiontorestrictoutagestothecircuitorequipmentaffected,accomplishedbythechoiceofovercurrentprotectivedevicesandtheirratingsorsettings.”
new Code
Article 100 Definitions. Coordination (Selective). Localizationofanovercurrentconditiontorestrictoutagestothecircuitorequipmentaffected,accomplishedbytheselectionandinstallationofovercurrentprotectivedevicesandtheirratingsorsettingsforthefullrangeofavailableovercurrents,fromoverloadtothemaximumavailablefaultcurrent,andforthefullrangeofovercurrentprotectivedeviceopeningtimesassociatedwiththoseovercurrents.
Elevators, Dumbwaiters, Escalators, Moving Walks, Platform Lifts, and Stairway Chairlifts 620.62 Selective Coordination. Wheremorethanonedrivingmachinedisconnectingmeansissuppliedbyasinglefeeder,theovercurrentprotectivedevicesineachdisconnectingmeansshallbeselectivelycoordinatedwithanyothersupplysideovercurrentprotectivedevices.
Selectivecoordinationshallbeselectedbyalicensedprofessionalengineerorotherqualifiedpersonengagedprimarilyinthedesign,installation,ormaintenanceofelectricalsystems.Theselectionshallbedocumentedandmadeavailabletothoseauthorizedtodesign,install,inspect,maintain,andoperatethesystem.
Emergency Systems 700.28 Selective Coordination. Emergencysystem(s)overcurrentdevicesshallbeselectivelycoordinatedwithallsupply-sideovercurrentprotectivedevices.
Selectivecoordinationshallbeselectedbyalicensedprofessionalengineerorotherqualifiedpersonsengagedprimarilyinthedesign,installation,ormaintenanceofelectricalsystems.Theselectionshallbedocumentedandmadeavailabletothoseauthorizedtodesign,install,inspect,maintain,andoperatethesystem.
Legally Required Standby Systems 701.27 SelectiveCoordination.Legallyrequiredstandbysystem(s)overcurrentdevicesshallbeselectivelycoordinatedwithallsupply-sideovercurrentprotectivedevices.
Selectivecoordinationshallbeselectedbyalicensedprofessionalengineerorotherqualifiedpersonsengagedprimarilyinthedesign,installation,ormaintenanceofelectricalsystems.Theselectionshallbedocumentedandmadeavailabletothoseauthorizedtodesign,install,inspect,maintain,andoperatethesystem.
708.54 Selective Coordination. Critical operations power system(s) overcurrent devices shall be selectively coordinated with allsupply-sideovercurrentprotectivedevices.
Selectivecoordinationshallbeselectedbyalicensedprofessionalengineerorotherqualifiedpersonsengagedprimarilyinthedesign,installation,ormaintenanceofelectricalsystems.Theselectionshallbedocumentedandmadeavailabletothoseauthorizedtodesign,install,inspect,maintain,andoperatethesystem.Exception: Selective coordination shall not be required between two overcurrent devices located in series if no loads are connected in parallel with the downstream device.
Mersen • NEC Code 2014 17
9. Selective Coordination Requirements, Continuedreasons for Changes
Thecodewasbeinginterpretedasallowinginstallationstohavelimitedcoordination,insteadoffullyselectivecoordination.Manypeoplewereunsureiftheyhadselectivecoordinationornot.Evensomeengineersdisagreedwhatthecoderequirementswereforcoordination.Someengineersreasonedthatifthesystemwascoordinatedonoverloads,itwasgoodenough.IEEEStandardshavedefinedselectivecoordinationformanyyearsandthemoreliberalinterpretationofselectivecoordinationwasnotincompliance.
Anexampleofanon-selectivelycoordinatedsystemiswhenabranchcircuitisshortedout,causingthefeederandmaybeeventhemaintode-energize.Thiscanhappeninatypicalbuildingthatwasnotdesignedwithselectivecoordinationasagoal.Thenwhyisituncommontoseeentirebuildingslosetheirpowerduetoabranchovercurrent?
Overcurrentscanbebrokenintotwotypes—overloadsandshortcircuits.Typicallyanoverloadislessthan10timestheratedcircuitcurrentandtheshortcircuitisover10times.Overloadsarethemostcommonelectricalproblem.Thesecommonoverloadsareveryeasytoselectivelycoordinatebecausemostfusesandcircuitbreakersaredesignedforthisperformance.Aslongastheupstreamovercurrentdevicehasahighertriprating,overloadsarealmostautomaticallycoordinated.
Thelesscommonovercurrentistheshortcircuit.Thisiswhenselectivecoordinationcanbecomeanengineeringtask.Unfortunately,shortcircuitsaremorelikelyduringafireorexplosionandthatisthesametimethatelevatorsandemergencyelectricalsystemsaremostneeded.Shortcircuitshavehighcurrentsandtheovercurrentprotectivedevicesrespondveryrapidly.Therapidresponsetimeshavetobecoordinatedsothatthesmallestportionoftheelectricalsystemistakenoutofservice.Ifthisisaccomplished,thesystemisselectivelycoordinated.
Electricalinspectorswerebeingaskedtoruleonthecomplianceofasystemtotheselectivecoordinationcoderequirements.Sinceevenengineerssometimesdisagreed,theelectricalinspectorswereputinadifficultposition.
how to ComPly
Thenewcodedefinitionisspecificthatthecoordinationmustbeforalltypesofovercurrentsindependentofhowlongtheprotectiondevicestaketooperate.Thisshouldresolvetheengineers’discussionabouttheintentofselectivecoordination.
Thecodecommitteefoundawaytohavetheelectricalinspectorenforcewithouthavingtobeanengineer.Thecoderequiresaqualifiedperson,acceptabletotheelectricalinspector,documenttheselectivecoordinationstatusoftheinstallation.Theelectricalinspectorcannowjustrequirethedocumentation.
Selectivecoordinationcanbeaccomplishedveryeasilywhenoriginallyselectingelectricalequipment.However,oncetheequipmentisonthejobsite,sometimestheadjustmentrangesofequipmentdonotpermitselectivecoordinationwithoutreplacingequipment.Theleastexpensivecircuitbreakertype,moldedcase,isproblematicforselectivecoordination.
helPful ProduCts
TheeasiestwaytocomplyistouseAmp-Trap2000fuses.Aslongasthesupplyfusesareatleasttwicetheampereratingoftheloadfuses,theAmp-Trap2000fusesareselectivelycoordinated.Thisfamilyoffusesgoesupthrough6,000amps.
TheMersenelevatorFusibleShuntPanelassistsineasyselectivecoordination.ItusesULClassJfusespermittingeasycoordinationbetweenupstreamfusesandupstreamcircuitbreakers.Thecurrent-limitingfusescutoffthefaultcurrentatalowenoughleveltoavoidtrippingtheupstreambreakerinmanyapplications.
18 Mersen • NEC Code 2014
10. Selective Coordination Not Required in HospitalsPrevious Code requirements
The2005Codeselectivecoordinationrequirementwasexpandedtohealthcarefacilities,emergencysystemsandlegallyrequiredstandbysystems.Theeffectsofthisexpansionwerewelldiscussedduringthe2008and2011codecycles,resultinginsomeclarification.Thecodemakingcommunityreviewedthebasicsofselectivecoordinationanddecidedtokeeptherequirementsforselectivecoordination.
Selectivecoordinationisadescriptionofhowanelectricalsystemactsunderovercurrents.Mostpeopleexpectthatasingleovercurrentinthesystemwouldde-energizethelocalproblemandlettherestofthesystemcontinuetooperate.Iftheelectricalsystemwasnotengineeredtobehaveasaselectivelycoordinatedsystem,alocalproblemcanresultinshuttingoffsubstantiallymoreofthesystemthannecessarytoisolatetheproblem.
Article517usedthephrase,“emergencysystem”inthedefinitionofhospitalessentialsystems.ThatmadehospitalessentialsystemssubjecttotherequirementsofArticle700EmergencySystems.ThereforeArticle517requiredselectivecoordination.
new Code
Health Care Facilities
517.2 Definitions. Critical Branch. Asystemoffeedersandbranchcircuitssupplyingpowerfortask illumination,fixedequipment,selectreceptacles,andselectpowercircuitsservingareasandfunctionsrelatedtopatientcareandthatisautomaticallyconnectedtoalternatepowersourcesbyoneormoretransferswitchesduringinterruptionofnormalpowersource.[99:3.3.30]
517.30 Essential Electrical Systems for Hospitals. (G) Coordination. Overcurrent protective devices serving the essential electrical system shall be coordinated for the periodoftimethatafault’sdurationextendsbeyond0.1second.
Exception No. 1: Between transformer primary and secondary overcurrent protective devices, where only one overcurrent protective device or set of overcurrent protective devices exists on the transformer secondary.
Exception No. 2: Between overcurrent protective devices of the same size (ampere rating) in series.
Informational Note: The terms coordination and coordinated as used in this section do not cover the full range of overcurrent conditions.
DeviceClosesttoFaultMustOpenWithoutOpeningUpstreamProtection
FaultedCircuit
Mersen • NEC Code 2014 19
10. Selective Coordination Not Required in Hospitals, Continued
reasons for Changes
TheNFPAorganizationdefineswhichcommitteehasjurisdictionoveroccupancies.NFPAassignedtheultimateresponsibilityforHealthCareFacilitieselectricalsystemstotheNFPA99committee.ThisHealthCareFacilitiesCodehas15chapters,oneofwhichiselectricalsystems.
Thismulti-disciplinecommitteedecidedthatselectivecoordinationshouldnotbearequirementinhospitals.TheNFPArulesdictatethattheNationalElectricalCodecannotcontradictNFPA99.AsresulttheNECCommitteeforHealthCareFacilitieswasdirectedtocomplywiththedeletionofselectivecoordinationrequirements.
TheNECcommitteethencomplied.Theychangedthedefinitionofessentialelectricalsystemstodeleteanyreferencetoemergencysystems.Thatdeletedthelinktotherequirementforselectivecoordination.ThentheyaddedverbatimthecoordinationrequirementfromNFPA99:3.3.30.FinallytheyaddedanInformationalNoteremindingthatcoordinationinthisarticledoesnotcoverthefullrangeofcurrents.
how to ComPly
TheNECrequirementisdeletedforselectivecoordinationinhospitals.Becausethepriorcodewasstricter,thereisnonewrequirement.However,becauseofpotentiallegalliabilityofnotcomplyingwithpreviouscodes,goodpracticewouldbetocontinuethepracticeofselectivecoordinationwiththehospital’sapproval.
Whendesigninganewelectricalsystem,thesectionsforselectivecoordinationshouldbeidentifiedfirst.Althoughcircuitbreakerscanbeselectivelycoordinatedforagivensystem,theuseoftheAmp-Trap2000familyoffusesismoreeconomical.
WithintheAmp-Trap2000familyoffusesasimple2:1ratioofthefusesizesensuresselectivecoordination.Thisisduetothecurrent-limitingactionofthefuseswhicharemuchfaster-actingthancircuitbreakers.Thereductionoftimeandcomplexityfromusingcircuitbreakersystemscanreducetheengineeringefforttocomplywiththeselectivecoordinationrequirements.
Ifthehospitalpreferscircuitbreakers,fusescanbeusedonlyasatransitionbetweensectionsoftheelectricalsystemthataredifficulttoselectivelycoordinate.
helPful ProduCts
TheselectivecoordinationrequirementcanbeeasilymetinnewsystemsdesignusingtheAmp-Trap2000familyoffuses.Thisfamilyenablesmeetingtherequirementseveniffutureelectricalsystemmodificationsvarytheavailablefaultcurrents.
TheMersenFusedCoordinationPanelboardenablesselectivityindifficultapplications.Itconsistsofcircuitbreakersandfusesarrangedinapanelboardtoeasilyachieveselectivecoordination.
TheElevatorSwitch,alsocalledtheFusibleShuntTripDisconnect,isbuiltforselectivecoordinationofelevatorapplications.Itfeaturesafiresafetyinterfacerelaywithafirealarmvoltagemonitoringrelayandmechanicallyinterlockedauxiliarycontacts.UseofMersen’sAmp-Trap2000ClassJfuseseasilypermitsselectivecoordination.
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