nec 690.12 rapid shutdown primer - hiq solar...1. “nfpa 70®: national electrical code® (nec®),...
Post on 11-Jul-2020
1 Views
Preview:
TRANSCRIPT
HiQSolar,Inc. Page1of6
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
HiQSolar,Inc. Page2of6
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.
NEC690.12RapidShutdownPrimerv1.0 9February2017
HiQSolar,Inc. Page3of6
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
NEC690.12RapidShutdownPrimerv1.0 9February2017
HiQSolar,Inc. Page4of6
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
NEC690.12RapidShutdownPrimerv1.0 9February2017
HiQSolar,Inc. Page5of6
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.
NEC690.12RapidShutdownPrimerv1.0 9February2017
HiQSolar,Inc. Page6of6
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.
top related