I would argue a single dedicated load circuit for the Enphase Envoy, in a dedicated inverter combiner panel, is code legal. Why? Because 705.12 states the distribution equipment must be capable of supplying "multiple branch circuits" for the 120% rule to apply. A single dedicated circuit for the Envoy appears to comply. Use a load center with a lockable cover if there are extra slots and you have done due diligence.
Kirk Herander VSE On Jun 27, 2012, at 11:51 AM, Jason Szumlanski <ja...@fafcosolar.com> wrote: > If you install a combiner panel that can supply additional branch circuits, > it becomes part of the building distribution system. Note that Enphase > recommends you install a branch circuit to supply power to the Envoy device > right from the combiner panel. If that is the case, the panel is certainly > part of the building distribution system and is obviously capable of > supplying branch circuits, in which case the 120% rule would apply. I don't > like it and I don't necessarily agree with it, but based on my strict > interpretation of the code I can see why an AHJ would require application of > this section in this case. > > Jason Szumlanski > Fafco Solar > > > > > On Wed, Jun 27, 2012 at 10:59 AM, Chris Mason <cometenergysyst...@gmail.com> > wrote: > I don't think this is expressed in the code, but in my opinion, the 120% > applies to the building distribution equipment, not to parts of the solar > system. In the case where a panel is being used to combine multiple inverter > outputs, the panel is part of the solar system only. The 120% rule was an > accommodation to allow solar to feed a building distribution panel and is not > applicable to solar system components. It would be good if the code could > indicate this more clearly. > > > On Wed, Jun 27, 2012 at 8:29 AM, Jason Szumlanski <ja...@fafcosolar.com> > wrote: > Kirk, > > That's basically what I said. Unfortunately, your opinion holds no weight > with my local AHJ's. I've argued the point till blue in the face. Although, I > have never had the instance where all available slots were filled in the > combiner panel - I might be able to argue that case successfully. > > Jason Szumlanski > Fafco Solar > > > > > On Tue, Jun 26, 2012 at 4:53 PM, Kirk Herander <k...@vtsolar.com> wrote: > Jason, > > > > In your email below you state: > > > > “You DO need to observe the 120% rule for the combining subpanel, regardless > of whether there are loads present, at least in jurisdictions where I have > worked. I've heard that some inspectors will allow you to ignore it if it is > labeled as a PV combiner with "add no loads" notation.” > > > > NEC 705.12 (D) states that the distribution equipment (in this case the > combiner panel, fed by multiple inverters and a utility source) must be > “capable of supplying multiple branch circuits or feeders or both” for (D)(1) > through (7) to apply. If you fully populated a combiner panel with inverter > breakers, leaving no slots for load breakers, it is not capable of supplying > branch circuits or feeders, and IMO the 120% rule does not apply to the > combiner buss or the conductors back to its point of utility interconnect. I > have argued this point as well as label combiners “load circuits prohibited” > (with or without available slots) and received AHJ approval. > > > > You could also just lock shut a combiner that had spare slots as a deterrent > to adding load breakers. > > > > > > Kirk Herander > > VT Solar, LLC > > dba Vermont Solar Engineering > > NABCEPTM Certified installer Charter Member > > NYSERDA-eligible Installer > > VT RE Incentive Program Partner > > 802.863.1202 > > > > From: re-wrenches-boun...@lists.re-wrenches.org > [mailto:re-wrenches-boun...@lists.re-wrenches.org] On Behalf Of Jason > Szumlanski > Sent: Tuesday, June 26, 2012 8:28 AM > To: RE-wrenches > Subject: Re: [RE-wrenches] Enphase grid tie question > > > > I'll email you off-list a 1-line diagram from a system with 164 > microinverters broken down into 8 strings in a 208V system. This particular > system used two subpanels to accumulate PV, but that was only because we had > to backfeed two existing subpanels due to the size of existing 480/208V > transformers. You will have to look at the utility service and all existing > equipment. > > > > Regarding the breakers in the subpanel, you will only need a maximum of a 20A > breaker for each string. The max inverters per string is 25 and the > calculation for OCPD is: > > > > 215W / 208V x 25 inverters / 1.732 x 1.25 = 18.65A > > > > “You DO need to observe the 120% rule for the combining subpanel, regardless > of whether there are loads present, at least in jurisdictions where I have > worked. I've heard that some inspectors will allow you to ignore it if it is > labeled as a PV combiner with "add no loads" notation.” > > > > Use a MLO panel with a fusible disconnect between the subpanel and the > interconnection point. If you use a 225A panel, you can feed it with 270A. > With eight 20A backfed PV circuits, you would need to protect the line side > of the panel with a 100A fusible disconnect. That probably isn't going to > work. You may be best off from a cost perspective using two 225A subpanels > and two 60A fusible disconnects. Anything larger than a 60A 3P disconnect and > the price skyrockets. It all depends on your circuit calculations and the > existing equipment. Of course, you would need two spaces for your > interconnection point. > > > > Jason Szumlanski > > Fafco Solar > > > > > _______________________________________________ > List sponsored by Home Power magazine > > List Address: RE-wrenches@lists.re-wrenches.org > > Options & settings: > http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org > > List-Archive: > http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org > > List rules & etiquette: > www.re-wrenches.org/etiquette.htm > > Check out participant bios: > www.members.re-wrenches.org > > > > > _______________________________________________ > List sponsored by Home Power magazine > > List Address: RE-wrenches@lists.re-wrenches.org > > Options & settings: > http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org > > List-Archive: > http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org > > List rules & etiquette: > www.re-wrenches.org/etiquette.htm > > Check out participant bios: > www.members.re-wrenches.org > > > > > > -- > Chris Mason > President, Comet Systems Ltd > www.cometenergysystems.com > Cell: 264.235.5670 > Skype: netconcepts > > > _______________________________________________ > List sponsored by Home Power magazine > > List Address: RE-wrenches@lists.re-wrenches.org > > Options & settings: > http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org > > List-Archive: > http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org > > List rules & etiquette: > www.re-wrenches.org/etiquette.htm > > Check out participant bios: > www.members.re-wrenches.org > > > > _______________________________________________ > List sponsored by Home Power magazine > > List Address: RE-wrenches@lists.re-wrenches.org > > Options & settings: > http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org > > List-Archive: > http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org > > List rules & etiquette: > www.re-wrenches.org/etiquette.htm > > Check out participant bios: > www.members.re-wrenches.org >
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