Download pdf - NEC 690.12 Rapid Shutdown Primer - HiQ Solarhiqsolar.com/wp-content/uploads/2018/11/hiq-solar-nec... · 2018-11-12 · NEC 690.12 Rapid Shutdown Primer v1.0 9 February 2017 HiQ Solar,

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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

NEC690.12RapidShutdownPrimerv1.0 9February2017


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.



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.

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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



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.



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.