This scenario is certainly allowed, but since it's not at the end of the feeder, either:
1. a. The feeder ampacity shall be not less than the sum of the primary source overcurrent device and 125 percent of the power-source output circuit current. 2. b. An overcurrent device at the load side of the power source connection point shall be rated not greater than the ampacity of the feeder. As with the feed-thru conductors, the idea is make them big enough or re-establish overcurrent protection, and protect busbars accordingly. 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 SEI Professional Services http://www.seisolarpros.com On Wed, Oct 28, 2020 at 2:48 PM Jason Szumlanski < ja...@floridasolardesigngroup.com> wrote: > 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 >>>> >>> _______________________________________________ > List sponsored by Redwood Alliance > > List Address: RE-wrenches@lists.re-wrenches.org > > Change listserver email address & settings: > http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org > > There are two list archives for searching. When one doesn't work, try the > other: > https://www.mail-archive.com/re-wrenches@lists.re-wrenches.org/ > http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org > > List rules & etiquette: > http://www.re-wrenches.org/etiquette.htm > > Check out or update participant bios: > http://www.members.re-wrenches.org > >
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