[RE-wrenches] Combining Multiple Inverters

[Jason Szumlanski]

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​





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

> ᐧ
> 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
>
> On Thu, Jun 26, 2014 at 9:20 AM, <
> 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>
>>
>> To: RE-wrenches <re-wrenches at lists.re-wrenches.org>
>> Subject: Re: [RE-wrenches] Combining Multiple Inverters
>> Message-ID:
>>         <
>> CAJJtG3oQGBLzatinUHFp_GhivzYD6dLdsLAnkc1ofG9tR1RFgA at mail.gmail.com>
>> Content-Type: text/plain; charset="utf-8"
>>
>>
>> 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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