[RE-wrenches] Combining Multiple Inverters

Fri Jun 27 17:12:19 PDT 2014

Jason,

It sounds like you want to get involved with the PV industry forum. We have about 30+ active members this year so your input would be welcome.

I think your idea about organization needs to be informed about some details. First of all, you need to read the new, very different, 705.12(D). SolarPro has a nice article about code updates.

Secondly, rules on the supply side are very different than load side. Supply side connections, by definition have no loads connected to them. It is simpler and does not need any 120% rule. The 120% rule is a very conservative restriction. No such restriction exists on the supply side.

Too much to cover all the issues now—suffice it to say there are many, many reasons to keep supply-side and load-side connections separate.

Bill.

From: RE-wrenches [mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Jason Szumlanski
Sent: Friday, June 27, 2014 5:45 AM
To: RE-wrenches
Subject: Re: [RE-wrenches] Combining Multiple Inverters

It depends on your applicable code. In the 2008 code, 690.64(B) was specifically titled "Load Side" and the provisions of that section in full were not applicable to supply side connections. That was probably not the intention (i.e. the 120% rule and OCPD requirements should have applied to aggregation panels). In the 2011 code, 705.12(D) is the similar section, but it has been titled "Utility Interactive Inverters." This section now "allows" load side connections, but the requirements (1) through (7) of this section still apply to supply side connections (my interpretation).

The better code organization IMO would be:

705.12 (A) Allow supply side connections

705.12 (B) Allow load side connections

705.12 (C) Integrated Electrical Systems

705.12 (D)(1)-(7) The requirements for all interconnection methods

705.12 (E) Greater than 100kW

A bit off-topic, but we recently had a utility reject a plan to install a 320A meter socket with a 200A main distribution panel and a 100A solar aggregation panel (with four 20A backfed breakers). The two panels were to be fed from double lugs in the meter can. They said this was not allowed - they didn't want solar in their meter can. When I pointed out that dual 200A load panels are commonly fed this way and this was no different because I could just backfeed each 200A panel with two 20A breakers, my comment was met with blank stares.

Jason Szumlanski

Fafco Solar

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On Thu, Jun 26, 2014 at 6:11 PM, Corey Shalanski <cshalanski at joule-energy.com <mailto:cshalanski at joule-energy.com> > wrote:

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Perhaps I should've been more specific with my scenario. I was imagining a supply side connection, as this would more commonly be the case when combining multiple inverters. In this case it seems like the provisions of 705.12(D) for load side conections don't even apply, no? Rather 705.12(A) becomes the relevant section, and I see very few restrictions there.

Even with a load side connection I would tend to agree with Jason's interpretation: Does the "source interconnection" in 705.12(D)(1) refer to each individual inverter, or can it refer to an aggregated "source"?

I am interested in pursuing this idea, mainly to understand how/where the NEC forbids it. In lieu of a clear Code reference against it, how is this any different from a branch circuit (in reverse)? ie, as with microinverters.

--

Corey Shalanski

Joule Energy

New Orleans, LA

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On Thu, Jun 26, 2014 at 9:20 AM, <re-wrenches-request at lists.re-wrenches.org <mailto:re-wrenches-request at lists.re-wrenches.org> > wrote:

Message: 11
Date: Thu, 26 Jun 2014 09:10:07 -0400
From: Jason Szumlanski <jason at fafcosolar.com <mailto:jason at fafcosolar.com> >

To: RE-wrenches <re-wrenches at lists.re-wrenches.org <mailto:re-wrenches at lists.re-wrenches.org> >
Subject: Re: [RE-wrenches] Combining Multiple Inverters
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705.12(D) reads, "... the interconnection provisions for the
utility-interactive inverter(s) shall comply with (D)(1) through (D)(7)."
That's inverters - plural. The interconnection must be protected by
dedicated OCPD, not each inverter individually. Microinverters comply
because of this interpretation.

That said, I've never done it. An accumulator panel is pretty cost
effective when you consider the alternative cost of an enclosure and the
Polaris connectors. I guess if you are making the Polaris connections
inside the main load center or inside an inverter you can eliminate the
cost of a dedicated enclosure. There would be some material and labor
savings.

?If the inverter has a maximum OCPD rating, you will be limited by that.
?Microinverters "get around" that by the wire and inverter being

sized/rated for the entire maximum string.

Jason Szumlanski

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