I forgot to include that it’s assuming a 200amp buss. Maybe you stated earlier what the buss rating is of the upper load center if so I missed it.
Jay > On Nov 8, 2020, at 10:02 AM, 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 >>>>> >>>>> 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 >> >> <Feed Through Lug Interconnection Option (2).pdf> >> _______________________________________________ >> 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. 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