[RE-wrenches] Paralleling Multiple Inverter

[William Miller]

Friends:

I have heard, but I have not researched myself, a provision in the code 
where one could dedicate a panel to be an "AC combiner" to collect the 
outputs of multiple inverters.  You would not install any branch circuit 
breakers and thereby eliminate the need to comply with the 120% rule.  This 
scenario  has never occurred in any projects we have designed, which is why 
I have not researched the code in this regard.

For a theoretic discussion, however, I wonder this:  Even though you have 
eliminated branch circuits from the equation, you still have the potential 
to overload the buss bars in or the feeder to the breaker panel in 
question.  If a fault occurs in the panel or feeder, you still have sum of 
the feeder breaker and the inverter breakers feeding the panel and the 
feeder in excess of what either is rated for.  Is this not a 
concern?  Faults can occur other than in branch circuits, faults such as a 
wrench dropped across the buss, backhoe fade, defective inverter breaker or 
compromised insulation.  Such a fault could cause catastrophic failure of 
the panel and/or feeder.  Has anyone else pondered this question?

William Miller

PS:  I realize a fault in the feeder means that you have fault current 
below the feeder rating from either direction, but what about at the point 
of the failure?

Wm



At 09:38 AM 1/22/2012, you wrote:
>Hi Nick,
>
>I see  (2011) 705.12 (d) where it talks about " supplying branch circuits 
>as the area where it changes.
>
>ie w/o branch circuits then all circuits are protected by the breakers as 
>long as the main buss isn't exceeded by the solar input of course.
>
>But in putting in that metering device plugged into a outlet, now you have 
>a branch circuit and hence the need to comply with 705.12 (D) 2.
>
>But I could be wrong.
>
>jay
>
>peltz power
>
>
>
>
>On Jan 22, 2012, at 8:36 AM, Nick Vida wrote:
>
>>That is very interesting Jay, do you have a code reference for no derate 
>>needed for your solar accumulation panel?
>>
>>Thanks,
>>
>>Nick Vida
>>
>>
>>btw- Rich, thanks for Bernie Sanders.
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Miller Solar
Voice :805-438-5600
email: william at millersolar.com
http://millersolar.com
License No. C-10-773985
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