[RE-wrenches] Combining Multiple Inverters

Mon Jun 30 12:14:20 PDT 2014

Bill,

I would be happy to contribute.

Regarding the 120% rule, I'm not sure I agree. There can be panelboards
connected in series in a supply side connection, and there can be loads in
PV inverter aggregation panels used in supply-side connections. For
example, it is common to install a dedicated outlet circuit for monitoring
gateways in microinverter system aggregation panels.

This below is compliant, and would have the same need for the 120% rule as
a load side connection if I understand the rationale correctly
(notwithstanding the way each code cycle is organized):

Supply<-->Fusible Disconnect<-->Aggregation Panel<-->Sub-Aggregation
Panels<-->PV Inverters and Loads

I'm not up to speed on the 2014 changes, so I'm really just talking about
the changes from 2008 to 2011, which seem to have moved in the direction of
applying 705.12(D)(1)-(7) to both load- and supply-side interconnected
systems in 2011, whereas 690.64(B)(1)-(7) in 2008 clearly applied to
load-side connections only.

Are you saying 705.12(D)(1)-(7) in 2011 apply to load-side connections
only? That's not the way I interpret it.

Jason Szumlanski

Fafco Solar

On Fri, Jun 27, 2014 at 8:12 PM, Bill Brooks <billbrooks7 at yahoo.com> wrote:

> 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
>
>
>
>
>
>
> 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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