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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

NationalElectricalCodeandN.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-reducingmaintenanceswitchallowsaworkertosetacircuitbreakertripunittonointentionaldelaytoreducetheclearingtimewhiletheworkerisworkingwithinanarc-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-Trap2000familydeliverscurrentlimitingfusesthatcanreducecostsandreducearcflashdangertoaminimumwhentheavailablefaultcurrentisadequate.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.ThissectioniscommonlycalledtheTapRules.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 manufacturers 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 manufacturers 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.

ThentheinstallermustinsurethatthepanelsSCCRisnotlessthantheavailablefaultatthesupplyterminalsofthepanel.FinallytheelectricalinspectorhastoverifythattheSCCRisonthenameplateandhavesomeevidencethattheSCCRisnotexceeded.

Compliancecanbecostlyifthepersonwhoisresponsibleforcodecomplianceignoresthiscodeissueuntiltheequipmentisinstalled.Extensivetimecanbeconsumedinnegotiatingwhoshouldpayfortheproblemresolution.Theinstallationfixoftenrequiresreturnofthepaneltothemanufacturerforupgrading.

helPful ProduCts

TheAmp-Trap2000familydeliverscurrent-limitingfusesthatcanincreasetheSCCRofindustrialcontrolpanels.ProductssuchastheUltraSafeTMUSFMfuseholderdirectlyreplacecircuitbreakershavingthesamewidthastypeIECstarters.TheSurge-Trapproductsprotectagainstvoltagespikesandhaveabuilt-inratingofupto200kASCCR.Thefinger-safepowerdistributionblockscanalsohavea100kAratingwithfuses.

10 Mersen NEC Code 2014

5. Solid-State Motor Protection with FusesPrevious Code requirements

Theformer430.52textusedthephrasingSuitablefuses,insteadofsemiconductorfuses.ItgavepermissiontosubstitutesuitablefusesfortherequirementsofTable430.52aslongastheequipmentwasmarkedtoidentifysuitablereplacementfuses.

SectionXAdjustable-Speed Drive SystemsofArticle430Motors,Motor Circuits and Controllershadnoinformationonshortcircuitandgroundfaultprotectiverequirements.Thatmeantthenon-adjustablespeeddrivecodesectionsprobablyapplied.

new Code430.52 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-faultprotectiveratingsarestipulatedforspecificdevicetypesinthemanufacturersinstructionsforthepowerconversionequipmentorareotherwisemarkedontheequipment,theyshallnotbeexceededevenifhighervaluesarepermittedby430.130(A)(1).

(3)Aself-protectedcombinationcontrollershallonlybepermittedwherespecificallyidentifiedinthemanufacturersinstructionsforthepowerconversionequipmentorifotherwisemarkedontheequipment.

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

Powerconversionequipmentshouldbecoordinatedwiththemanufacturersinstructions.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

MersensPVSafetySystemhasbeenprovidinganIECrapidPVshutdowncapabilityinEuropeforsometime.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?

Overcurrentscanbebrokenintotwotypesoverloadsandshortcircuits.Typicallyanoverloadislessthan10timestheratedcircuitcurrentandtheshortcircuitisover10times.Overloadsarethemostcommonelectricalproblem.Thesecommonoverloadsareveryeasytoselectivelycoordinatebecausemostfusesandcircuitbreakersaredesignedforthisperformance.Aslongastheupstreamovercurrentdevicehasahighertriprating,overloadsarealmostautomaticallycoordinated.

Thelesscommonovercurrentistheshortcircuit.Thisiswhenselectivecoordinationcanbecomeanengineeringtask.Unfortunately,shortcircuitsaremorelikelyduringafireorexplosionandthatisthesametimethatelevatorsandemergencyelectricalsystemsaremostneeded.Shortcircuitshavehighcurrentsandtheovercurrentprotectivedevicesrespondveryrapidly.Therapidresponsetimeshavetobecoordinatedsothatthesmallestportionoftheelectricalsystemistakenoutofservice.Ifthisisaccomplished,thesystemisselectivelycoordinated.

Electricalinspectorswerebeingaskedtoruleonthecomplianceofasystemtotheselectivecoordinationcoderequirements.Sinceevenengineerssometimesdisagreed,theelectricalinspectorswereputinadifficultposition.

how to ComPly

Thenewcodedefinitionisspecificthatthecoordinationmustbeforalltypesofovercurrentsindependentofhowlongtheprotectiondevicestaketooperate.Thisshouldresolvetheengineersdiscussionabouttheintentofselectivecoordination.

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,emergencysysteminthedefinitionofhospitalessentialsystems.ThatmadehospitalessentialsystemssubjecttotherequirementsofArticle700EmergencySystems.ThereforeArticle517requiredselectivecoordination.

new CodeHealth 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 periodoftimethatafaultsdurationextendsbeyond0.1second.

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,goodpracticewouldbetocontinuethepracticeofselectivecoordinationwiththehospitalsapproval.

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.UseofMersensAmp-Trap2000ClassJfuseseasilypermitsselectivecoordination.

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