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 SEI Professional Services http://www.seisolarpros.com 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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