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 > <[email protected]> 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 >> <[email protected]> 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 >>> <[email protected]> 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 <[email protected]> >>>> 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 >>>>> <[email protected]> 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: [email protected] > > 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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