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NEC 690.12 Rapid Shutdown Primer - HiQ Solar...1. “NFPA 70®: National Electrical Code® (NEC®),...

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HiQ Solar, Inc. Page 1 of 6 NEC 690.12 Rapid Shutdown Primer Introduction The 2014 edition of the National Electrical Code 1 (NEC) was the first to introduce a mandatory requirement called Rapid Shutdown, intended as an aid to firefighters by reducing the risk of shock hazard when fighting fires. This new requirement applies to PV systems on buildings in the US and is contained in Section 690.12 of the 2014 and later editions of the NEC. At a high level the requirement is that controlled conductors must be at safe voltage levels quickly after initiation of Rapid Shutdown. Controlled conductors were defined in the 2014 edition as any conductor more than 10 feet from the PV array. Since then the requirements have evolved further in the 2017 edition. This article is not intended to be academically thorough or rigorous – some excellent articles are listed at the end for those that need depth. This is a general overview focused on 3-phase commercial inverter installations. Summary of Requirements A brief overview of how the Rapid Shutdown requirements have evolved is given in Table 1. 690.12 Rapid Shutdown evolution No requirement <30V beyond 10’ of the array boundary within 10s [i] <30V beyond 1’ of the array boundary within 30s 80V max within array boundary NEC 2011 and prior NEC 2014 NEC 2017 NEC 2017 after 1 st Jan, 2019 Table 1: Overview of Rapid Shutdown requirements [i] Since increased to 30s – see later in this document
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Page 1: NEC 690.12 Rapid Shutdown Primer - HiQ Solar...1. “NFPA 70®: National Electrical Code® (NEC®), 2014 Edition”, by National Fire Protection Association 2. Article in SolarPro

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NEC690.12RapidShutdownPrimer

IntroductionThe2014editionoftheNationalElectricalCode1(NEC)wasthefirsttointroduceamandatoryrequirementcalledRapidShutdown,intendedasanaidtofirefightersbyreducingtheriskofshockhazardwhenfightingfires.ThisnewrequirementappliestoPVsystemsonbuildingsintheUSandiscontainedinSection690.12ofthe2014andlatereditionsoftheNEC.AtahighleveltherequirementisthatcontrolledconductorsmustbeatsafevoltagelevelsquicklyafterinitiationofRapidShutdown.Controlledconductorsweredefinedinthe2014editionasanyconductormorethan10feetfromthePVarray.Sincethentherequirementshaveevolvedfurtherinthe2017edition.Thisarticleisnotintendedtobeacademicallythoroughorrigorous–someexcellentarticlesarelistedattheendforthosethatneeddepth.Thisisageneraloverviewfocusedon3-phasecommercialinverterinstallations.

SummaryofRequirementsAbriefoverviewofhowtheRapidShutdownrequirementshaveevolvedisgiveninTable1.

690.12RapidShutdownevolution

Norequirement <30Vbeyond10’ofthearrayboundarywithin

10s[i]

<30Vbeyond1’ofthearray

boundarywithin30s

80Vmaxwithinarrayboundary

NEC2011andprior ✔ NEC2014 ✔ NEC2017 ✔ NEC2017after1stJan,2019 ✔Table1:OverviewofRapidShutdownrequirements

[i]Sinceincreasedto30s–seelaterinthisdocument

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2014NECRequirementsThefollowingistakenfromtheBillBrooksarticlelistedattheend2,andgivestheexactwordingoftheRapidShutdownrequirementinthe2014code,asfollows:“690.12RapidShutdownofPVSystemsonBuildingsPVsystemcircuitsinstalledonorinbuildingsshallincludearapidshutdownfunctionthatcontrolsspecificconductorsinaccordancewith690.12(1)through(5)asfollows.(1)RequirementsforcontrolledconductorsshallapplyonlytoPVsystemconductorsofmorethan1.5m(5ft)inlengthinsideabuilding,ormorethan3m(10ft)fromaPVarray.(2)Controlledconductorsshallbelimitedtonotmorethan30voltsand240volt-ampereswithin10secondsofrapid-shutdowninitiation.(3)Voltageandpowershallbemeasuredbetweenanytwoconductorsandbetweenanyconductorandground.(4)Therapid-shutdowninitiationmethodsshallbelabeledinaccordancewith690.56(B).(5)Equipmentthatperformstherapidshutdownshallbelistedandidentified.”Sincethislanguagewasintroduced,aTIA(TentativeInterimAmendment)hasbeenissuedthatrelaxestheallowedtimelimitfrom10sto30s3,4withaneffectivedateof24thAugust,2016.

DiscussionOpeningtheACdisconnectservingautility-interactiveinvertercausestheinvertertoshutdown(UL1741anti-islandingrequirementsmandatethisforutility-interactiveinvertersintheUS).However,thisdoesn’tensurethatallconductorsontheDCsidebetweentheinverterandthePVarraywillbecomede-energized–thePVmoduleswillstillbeproducingavoltageanytimethereissufficientirradiance.Commonpracticeforcentralandstringinverterinstallationshasbeentomounttheinvertersonawallordownontheground,andtoinstalllongrunsofwireuptothePVarray.TheRapidShutdownrequirementcomplicatesthis–shuttingtheinverteroffdownonthegrounddoesn’tde-energizetheDCwiresrunninguptotheroof.Anobviousnextstepistoputremote-controlledorauto-sensingDCdisconnectswithin10feetofthearray,andsuchproductsareavailableforsale.Unfortunatelythereareseveralproblemswiththisapproach.Firstlyitaddsextracost,installtime,complexityandpointsoffailure.Secondly,whentheDCsideofsomeinvertersgoesopen-circuit,capacitorsinsidetheinverterkeepthevoltagehighforupto5minutes(amaximumtimeallowedbyUL1741.)Thisisfarlongerthantheallowedtimerequiredbytheoriginallanguageofthe2014NEC.Forthereasonsmentionedaboveitisincreasinglycommontomountinvertersontheroof,withinthedefinedboundaryofthearray.DoingthismeansthatonethrowoftheACdisconnectshutstheinvertersdown,andanyhighDCvoltagesarewithintheboundaryofthearray,wheretheyareallowed.Anoverviewofdifferentapproachestocomplyingwiththe2014requirementsisshowninFigure1.

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Figure1: DifferentapproachestocomplyingwiththeRapidShutdownrequirement.(a)Centralandwall-mountedstringinvertersoftenaddanintelligent(i.e.expensive)DCdisconnectswitch(b)thatsenseswhentheinverterhasshutdownanddisconnectsthearray.Alternatively(c)hasthestringinvertermountedwithin10feetofthearrayonacradle.(d)TheHiQTrueStringinvertertucksnaturallyunderthearrayandeasilyfulfillsthe10’and1’requirementsforRapidShutdown

2017NECRequirementsThesectiondealingwithRapidShutdownhasbeensignificantlyexpandedinthe2017edition5.Again,BillBrooksprovidesagoodsummary,listedattheendofthispaper6.Ofthemanyupdatesmade,thefollowingarenotableinthecontextof3-phaseinverters:

• Thearrayboundarynowhasa1’perimeterfromtheedgeofthePVmodulesinsteadof10’.• EquipmentmustbespecificallycertifiedforRapidShutdownuse.• Therearethreewaysthatanarraycanbecompliant:

o Thespecificcomponentpartstogetherarelistedasanassemblytocomply.o Thearrayhasnoexposedmetal,andismorethan8’awayfromanygroundedmetalo Withinthearrayboundariesthereisnoconductorwithavoltagehigherthan80Vwhen

RapidShutdownisinitiated.ThisdifferssignificantlyfromtheNEC2014requirement,asDCconductorscouldstillbeatupto1,000Vinsidetheboundaryaftershutdownisinitiated.

Theserulesrequireequipmentthatcomplies,whichconsequentlymeansthatmethodsmustbedevelopedforcertifyingtheequipment.Forthisreason,theimplementationisphased–whilethe‘1’rule’isinimmediateeffectforstatesthathaveadoptedthe2017NEC,therulesrestrictingthevoltageto80Vinsidethefootprintofthearrayarenotduetocomeintoeffectuntil1stJanuary,2019.Therearemanyotherrequirements,includingthelabelingandaccessibilityofshutdownswitchesetc.–refertothe2017NECformoredetails.

10#

1#

(a)

(c)

(d)

(b)

Manda

tedWa

lkway

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References1. “NFPA70®:NationalElectricalCode®(NEC®),2014Edition”,byNationalFireProtection

Association2. ArticleinSolarPromagazinebyBillBrooks,January2015:“RapidShutdownforPVSystems:

UnderstandingNEC690.12”http://solarprofessional.com/articles/design-installation/rapid-shutdown-for-pv-systems?v=disable_pagination

3. TIA14-10,effectivedateAugust24th,2016.http://www.nfpa.org/assets/files/AboutTheCodes/70/TIA_70_14_10.pdf

4. http://ecmweb.com/news/nfpa-issues-three-tias-related-2014-nec5. “NFPA70®:NationalElectricalCode®(NEC®),2017Edition”,byNationalFireProtection

Association6. PresentationtoAEEDealerConferencebyBillBrooks:http://aeesolar.com/wp-

content/uploads/2017/01/2017DC-Rapid-Shutdown-2017-NEC.pdf

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Appendix:HiQSolar’sTrueStringInvertersandthePushforArrayMountingWhenitcomestoarraymounting,notallinvertersarecreatedequal.Ifyou’reamanufacturerofcentralinvertersyouarequietlycryingatthispoint,andamakerofmicroinverterscheeringloudly.However,microinvertersareusuallytooexpensiveforcommercialrooftops,andcentralinvertersarebeingusedlessandlessinfavorof3-phasestringinverters.Sotheproblemfacedbymanyinstallersisthattheywanttouse3-phasestringinverters,butsomehowhavetocomplywiththeRapidShutdownrequirement.Most3-phasestringinvertersweredesignedtobemountedverticallyonawallinashelteredenvironment.Usuallytheycannotlieflatontheirbacks.TheyalsofrequentlyhaveLCDscreensgivingsysteminformation,andtheseareknowntoneedfrequentreplacementwhenusedindirectsunlightandharshenvironments.However,it’snotusuallypracticaltobuildasuitablewalltomounttheseinverterson,whichiswhyattemptsarebeingmadetomountthemonangledcradlessuchasisillustratedinthepictureatthestartofthisdiscussion.It’sobviousthatthisisnoone’sideaofaperfectsolution.

CradleCompromisesorPurpose-DesignedSolutionTheHiQSolarTrueStringinvertersweredesignedfromtheoutsettobearray-mounted.Belowisaquickcomparisonofourapproachwiththelarge3-phasestringinvertersthatareincreasinglycommon. 3-phaseStringonaCradle

HiQTrueStringmountedunderthearray

1. Satisfies2014NEC

690.12RapidShutdown10’rule?

Wheninstalledcorrectlyandwithin10feetofthearray,yes

Wheninstalledcorrectlyandwithin10feetofthearray,yes

2. Satisfies2017NEC690.12RapidShutdown1’rule?

Possible,butawkward-notdesignedforthis

Wheninstalledcorrectlyandwithin1footofthearray,yes

3. Easeofdesigningwith

Requiresextrawidewalkwaysortakesupspaceinmandatedwalkways

Sitsunderthearray,buteasytoaccessunlikemicroinverters

4. Easeofinstallation

Typicallyweighmorethan150lb.,hardtolift,requiresmorethanoneperson.Requiresextraeffortandcosttobuyandassemblethecradle

Weighs24lb.Easytolift,easytoinstall,easytocarryspares.Easytoinstallbyoneperson.Connector-basedelectricalconnections.

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3-phaseStringonaCradle

HiQTrueStringmountedunderthearray

5. Reliability LCDs,fansetc.requiremaintenance

andregularreplacement.Oftentheseinvertersuseelectrolyticcapacitors.Sitsinfullsun.Notbeingusedasoriginallyintended

NEMA6,noelectrolytics,nodisplay,nofans.Maintenance-free.Robust,singlecircuitboard,automotivegradecomponents.Beingusedasintended

6. Easeofreplacementlater

150lb.+,hardtogetreplacementunitsontoarooflater,requiresseveralpeopleinthecrewtodoso

Tuckoneunderyourarm,climbaladder.Unclicktheconnectors,clickinthenewone.Easy

7. Other Usuallystringsareparalleled,makingpoorgranularityofmonitoring,fault-findingandarcdetection

EachstringhasseparateMPPT,monitoring.Singlestringarcdetection,placednexttothemodules,makesarcdetectionreliabilitybetter,andreducesoccurrenceoffalse-positives

SummaryHiQ’sTrueStringinvertersweredesignedtobemountedinmanylocations,includingunderthePVarray,andnaturallycomplywiththerequirementsof690.12oftheNEC. TheHiQsolutionalsoprovidesadditionalbenefitsofreducedcost,easierinstallationandmaintenance.


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