[RE-wrenches] Multiple inverters

[Christopher Warfel]

I know I keep popping up on this, but 2014 makes no sense if it is 
saying to connect multiple inverters to one disconnect. It would be 
difficult and dangerous to take one out of service for any reason 
including replacement. I would that that you'd have to shut down all the 
inverters just to replace one. Some of the large 
commercial/industrial/utility systems have hundreds of inverters and 
there is no way they would install a system to this interpretation of 
the NEC.

On 2/27/2019 12:22 PM, Starlight Solar Power Systems wrote:
> William,
>
> It seems this question needs to be addressed: What is the intended 
> meaning of “installed in one system” in 2014? If you have separate 
> “systems”, they should not be governed by 705.12. So, at what point 
> does a “system” begin and end? PV modules to the disconnect? ...to the 
> load panel? ...to the service entrance?
>
> Larry
>
>
> On Feb 25, 2019, at 10:42 PM, William Miller <william at millersolar.com 
> <mailto:william at millersolar.com>> 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:
>
> <image001.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.
>>
>> Thisarticle 
>> <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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