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 <[email protected]> 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:* [email protected] [mailto: > [email protected]] *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: [email protected] > > 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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