[RE-wrenches] Multiple inverters
Christopher Warfel
cwarfel at entech-engineering.com
Tue Feb 26 08:47:39 EST 2019
If you live by the language, and there are multiple interpretations of
the language, then you need to follow the AHJ since they have ultimate
authority. Probably many people on this list have been involved in
discussion of interpreting the NEC. That's one of the functions of the
WRENCHES listserv. I've inspected many systems for various entities, and
with regard to string inverters, they require their own disconnecting
means and have for many code cycles.. If you think that it says that
multiple inverters may only be interconnected by one OCPD, then I would
verify with AHJ and follow what he/she requires. I could read your
citation that each inverter shall be made at a dedicated circuit
breaker. That's my interpretation. The 2014 is known to have a number
of problems. The NEC also suggests that you use best practices. Chris Warfel
On 2/26/2019 12:42 AM, William Miller wrote:
>
> August:
>
> The 2014 code, which the AHJ for this project is using, states the
> following:
>
> (/1) Dedicated Overcurrent and Disconnect. The source/
>
> /interconnection of one or more inverters installed in one/
>
> /system shall be made at a dedicated circuit breaker or fusible/
>
> /disconnecting means./
>
> Note that the language says, “The source interconnection…” (singular),
> and “at a dedicated circuit breaker…”(again singular). This makes it
> obvious to me that the language says that the outputs of multiple
> inverters need to be aggregated and connected via _one_ OCPD. I think
> the other wrenches missed this point.
>
> Your input is valuable by contrasting the language of the 2014 code
> with that of the 2017 version. The inclusion of the phrase “Each
> source…” in the 2017 code completely changes the meaning. Some AHJs
> will look to future code versions for clarity even if they are not yet
> adopted. I think this is a good thing, and I really appreciate you
> bringing up the new language.
>
> The article from AEIA magazine ratifies the conclusion I drew from the
> 2014 code. Fortunately the AHJ is misinterpreting the section to
> allow the more liberal interpretation, the one that the 2017 code
> reflects. I find it best to contact the plan checker directly, which
> I did, and we are approved for multiple OCPDs. By the way, I think
> that article is well written and I have book marked it.
>
> I don’t know if the 2014 language was a mistake corrected in 2107, or
> what the thinking was of the authors. Regardless, we live by the
> language, not the intent.
>
> Thank you as well to all who responded.
>
> William Miller
>
> *From:*August Goers [mailto:august at luminalt.com
> <mailto:august at luminalt.com>]
> *Sent:* Monday, February 25, 2019 9:07 AM
> *To:* William Miller; RE-wrenches
> *Subject:* Re: [RE-wrenches] Multiple inverters
>
> Hi William -
>
> In this case, it is helpful to look forward to the 2017 NEC for guidance:
>
> image.png
>
> I believe it's perfectly fine to have multiple inverter breakers in
> your main.
>
> August
>
> Luminalt
>
> On Mon, Feb 25, 2019 at 8:42 AM William Miller
> <william at millersolar.com <mailto:william at millersolar.com>> wrote:
>
> Friends:
>
> I have an NEC code question on an upcoming project. It is a home
> that has an existing 8 kW ground-mounted grid-tied system. The
> owner wants to add another 10 kW of grid-tied PV. My question is
> about 705.12, point of connection. Specifically section (D)(1).
> That section states:
>
> /The source interconnection of one or more inverters installed in
> one system shall be made at a dedicated circuit breaker or fusible
> disconnecting means./
>
> So if there are going to be two inverters on premise, do the
> outputs have to be aggregated to connect via one circuit breaker?
> This might be difficult to do as the exiting inverter is connected
> via a different sub-panel than the one that is planned to receive
> the new inverter output.
>
> This article
> <https://iaeimagazine.org/magazine/2014/01/16/load-side-pv-connections/>
> addresses the question.
>
> I would be very grateful if any of you can share any experience
> you might have in interpreting this section of the code.
>
> Thanks in advance.
>
> William
>
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--
Christopher Warfel
ENTECH Engineering, Inc.
PO Box 871, Block Island, RI 02807
401-466-8978
<http://entech-engineering.com>
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