For further discussion, I don't see how my original scenario is any different from this attached scenario, which I think everyone would agree is allowed. All conductors and busbars are subject to the same potential loads and fault currents. (Image attached).
On Wed, Oct 28, 2020 at 5:01 PM Jason Szumlanski < ja...@floridasolardesigngroup.com> wrote: > Of course the feeder conductors and bus bar could be subjected to a fault. > But we're not talking about faults here. Fault protection is the job of the > PV OCPD And primary supply OCPD to protect the downstream busbar and > feeders. If that wasn't the case, you would need a new OCPD on BOTH the > load and line side of a solar connection as a feeder tap, not just the load > side. > > If your interpretation is correct regarding the location of the OCPD, that > sounds like a sub-feed breaker is the only way to comply, and I haven't > seen such an animal for a typical residential load center. You can get > these for NQ panelboards and similar panelboards from other manufacturers > of course. It doesn't say as close as practicable or anything like that. It > says that a busbar connection is allowed when there are feeder CONDUCTORS > connected to feed through LUGS. What does "overcurrent device .. *at* the > supply end" mean? I emphasize "at." It's unclear how you would implement > this other than a sub-feed breaker I suppose, but that's not what it says. > It refers to feeder conductors on lugs on busbars, not feeder conductors on > load-side terminals of an overcurrent device. > > My point is that 705.12 should have been wrapped up neatly in a bow, but > the lack of clarity, still, is astonishing. Why add a section about > feed-through lugs if it's going to be so vague? > > Jason > > > > > On Wed, Oct 28, 2020 at 3:37 PM Brian Mehalic <br...@solarenergy.org> > wrote: > >> Hey Jason, >> Here's the 2020 text: >> >> 6) Connections shall be permitted on busbars of panelboards that supply >> lugs connected to feed-through conductors. The feed-through conductors >> shall be sized in accordance with 705.12(B)(1). Where an overcurrent device >> is installed at the supply end of the feed-through conductors, the busbar >> in the supplying panelboard shall be permitted to be sized in accordance >> with 705.12(B)(3)(1) through 705.12(B)(3)(3). >> >> >> The OCPD on the supply end of the feed-through conductors would be in the >> form of a sub-feed breaker at the point of supply to those conductors, >> re-establishing overcurrent protection of the conductors (likely at the >> same ampacity as the main breaker in the supplying panel. The feed-through >> conductors are basically an extension of the busbar in the supplying panel; >> they can either be protected by the main, or in the presence of multiple >> sources of power in the supplying panel (such as a backfed PV system >> breaker) they can be protected based on (B)(3)(1) - "the 125% rule" - or >> they can be protected by a new overcurrent device at their point of supply, >> in which case current on them is limited based on that OCPD size; in this >> latter scenario the busbar in the supplying panel is allowed to be sized >> based on one of (B)(3)(1) - (3) because it is protected downstream at its >> end. >> >> The theory is pretty much the same as 705.12(B)(1) for feeders - when not >> connecting at the end of the feeder, use the "125% rule" or re-establish >> overcurrent protection for that portion of the feeder subject to multiple >> power sources. >> >> In your drawing the 200 A feeder conductors, as well as the busbar below >> the PV system breaker, could be subject to > 200 A in the event of a fault >> somewhere along those conductors. >> >> Brian Mehalic >> NABCEP Certified Solar PV Installation Professional™ R031508-59 >> National Electrical Code® CMP-4 Member >> (520) 204-6639 >> >> Solar Energy International >> http://www.solarenergy.org >> <https://mailtrack.io/trace/link/6861d7d8805b342c05a1945424d5d3679153b6c2?url=http%3A%2F%2Fwww.solarenergy.org&userId=1613865&signature=755f4d3125876434> >> >> SEI Professional Services >> http://www.seisolarpros.com >> <https://mailtrack.io/trace/link/56a599fdf28222e003dcf7711461480ee5165051?url=http%3A%2F%2Fwww.seisolarpros.com&userId=1613865&signature=68c217cadacd349b> >> >> >> >> On Wed, Oct 28, 2020 at 10:18 AM Jason Szumlanski < >> ja...@floridasolardesigngroup.com> wrote: >> >>> Does anyone else think they botched the wording in this section? It's >>> still not clear, and we have a ton of meter/main combos with feed-through >>> lugs around here. >>> >>> Where is it written, "where an overcurrent device is installed at the >>> *supply >>> end* of the feed-through conductors," (emphasis added) are they >>> referring to the solar backfed breaker on the busbar or another breaker >>> somewhere along the feeder circuit? It goes on to state that the loads on >>> the supplying busbar can comply with any method in 705.12(B)(3), which >>> prescribes an OCPD at the load end of the feeder in 705.12(B)(3)(3), so >>> they can't be talking about that. I have to assume it is the solar >>> backfed breaker they are referencing. >>> >>> See my interpretation of one scenario in the attached image. >>> >>> We're a long way off from the 2020 code implementation here, but it can >>> help sway plans examiners looking to clarify the intent of the 2014/2017 >>> code cycles. >>> >>> >>> Jason Szumlanski >>> >>
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