Also in 2014 we get 705.12(D)(2)(3)(c) which should be very useful in distribution panelboards.
-N On Thu, Mar 27, 2014 at 3:00 PM, Brian Mehalic <[email protected]>wrote: > The "120% rule" in 2014 is 705.12(D)(2)(3)(b). Ugh. Anyway, the inverter > current is "125 percent of the inverter(s) output circuit current", aka the > minimum OCPD and conductor ampacity value per 705.60(B) and 690.8(B)(1). > > This is actually a bit of wiggle room: in 2011 the 120% rule was based on > the inverter output circuit OCPD size, which is often larger than 125% of > the inverter output circuit current. > > Cheers, > > > Brian Mehalic > NABCEP Certified Solar PV Installation Professional(tm) R031508-59 > IREC ISPQ Certified Affiliated Instructor/PV US-0132 > > PV Curriculum Developer and Instructor > Solar Energy International > http://www.solarenergy.org > > > On Thu, Mar 27, 2014 at 2:34 PM, Troy Harvey <[email protected]>wrote: > >> I am wondering about the busbar 120% rule, and if there is any wiggle >> room in the 2014 NEC. >> >> Fundamentally I don't understand the 120% rule. If my solar breaker is >> installed properly at the bottom of the busbar, and the grid-tie breaker is >> installed at the top, and the busbar itself is rated for 120% of the panel >> rating, I don't see any means by which a solar breaker of a size >> substantially larger than 120% could cause a problem. There can be no >> place on the busbar under any situation (that I can think of) that would >> exceed 120% because the supply current is coming from opposite ends of the >> bus bar - even in the worst case load situation. So even if I had a huge PV >> system (100A), backfeeding the bottom of a 200A panel, I don't see a >> situation where there is more than 200A over any one section of busbar. Am >> I wrong, or is the NEC just too prescriptive for its own good? >> >> Also would you say that the 120% is based on the inverter max output or >> backfeed breaker size? >> >> >> thanks, >> >> Troy Harvey >> --------------------- >> Principal Engineer >> Heliocentric >> 801-453-9434 >> [email protected] >> >> >> >> >> _______________________________________________ >> List sponsored by Home Power magazine >> >> List Address: [email protected] >> >> Change email address & settings: >> http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org >> >> List-Archive: >> http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org >> >> List rules & etiquette: >> www.re-wrenches.org/etiquette.htm >> >> Check out participant bios: >> www.members.re-wrenches.org >> >> >> > > _______________________________________________ > List sponsored by Home Power magazine > > List Address: [email protected] > > Change email address & settings: > http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org > > List-Archive: > http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org > > List rules & etiquette: > www.re-wrenches.org/etiquette.htm > > Check out participant bios: > www.members.re-wrenches.org > > > -- Nathan Charles Engineer NABCEP Certified PV Installation Professional #042013-20 Paradise Energy Solutions (717) 283-2021 direct
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