The code clearly allows a 400A supply (200 main plus 200 solar supply) to a 200A bus if there are no loads on that bus. Or a 300A total supply to a 200A bus with 100A of loads. That's 705.12(D)(2)(3)(c) verbatim.
Better get an insulated wrench. On Mon, Nov 9, 2020 at 12:53 PM William Miller <will...@millersolar.com> wrote: > . Where would 300A of current ever flow? > > > > What is someone dropped a wrench on the bus? It would fault with greater > than 200 amps. This is and has been the point behind this code section. > > > > William > > Miller Solar > > 17395 Oak Road, Atascadero, CA 93422 > > 805-438-5600 > > www.millersolar.com > <https://mailtrack.io/trace/link/45f3322dcff8c8848aab527a83b7e9721f4281ff?url=http%3A%2F%2Fwww.millersolar.com%2F&userId=1613865&signature=5109dabe048e7da1> > > CA Lic. 773985 > > > > > > *From:* RE-wrenches [mailto:re-wrenches-boun...@lists.re-wrenches.org] *On > Behalf Of *Jason Szumlanski > *Sent:* Sunday, November 8, 2020 9:47 AM > *To:* RE-wrenches > *Subject:* Re: [RE-wrenches] NEC 2020 - 705.12(B)(6) > > > > It's a 200A bus. > > > > 300A "on" the bus doesn't matter. The total of all load and supply devices > does not exceed the bus rating. This is 705.12(D)(2)(3)(c) in 2014/2017. > > > > In no way can the total ampacity on the 200A bus exceed 200A as long as > additional loads are not added, hence the required warning label > > > > On Sun, Nov 8, 2020, 12:30 PM Jay <jay.pe...@gmail.com> wrote: > > Hi Jason > > > > My question is if it’s 200a in from the main breaker and 100a from PV its > 300 amps on the buss correct? > > > > How is that ok with the 125% rule? > > > > Or is this covered by some other rule as it’s a feed through lug load > center? > > > > Jay > > > > > > > > On Nov 8, 2020, at 9:46 AM, Jason Szumlanski < > ja...@floridasolardesigngroup.com> wrote: > > > > Maybe this is a better example (attached). I don't see how this would be a > problem under NEC 2014, 2017, or 2020. No portion of the main bus, feeder > conductors, or subpanel could possibly be subjected to overcurrent without > an OCPD stopping it. > > > > My point is that here we are, 3 code cycles in since feeder taps were > addressed, and there is still no clarification of intent. AHJs are still > struggling with this. > > > > I'm not sure where residential meter/mains with feed through lugs are > popular. I know they are in Florida and I have heard Hawaii. I'm curious > what your jurisdictions think of this if you have this scenario. Most of > the time the subpanel is main lug only, but adding a main circuit breaker > is usually an easy and cost-effective fix to make this interconnection type > work. > > > > Jason Szumlanski > > > > > > > > > > > > On Wed, Oct 28, 2020 at 5:15 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/2603da024a6946c42b34ebf7b2750490f5e01be5?url=http%3A%2F%2Fwww.solarenergy.org&userId=1613865&signature=32a5d3726246f3bd> > > > > SEI Professional Services > > http://www.seisolarpros.com > <https://mailtrack.io/trace/link/2b1457686471c2ca8a6962c8f5b7342d186c2f85?url=http%3A%2F%2Fwww.seisolarpros.com&userId=1613865&signature=678c2944003a1fb2> > > > > > > > > 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 > > *Error! Filename not specified.* > > *Error! 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