Line-side tap minimum AC disconnect rating: 30A or 60A?

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photonboy

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Berkeley, CA, USA
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Ex roof monkey, current desk jockey
We have a residential install with a line side tap where the max output of the inverter x 1.25 = 26.25A. The fused AC disco is 30A rated with 30A fuses.

We had an engineering firm assess the project and they stated that the AC disco must have a minimum rating of 60A based on NEC 230.79 (D).

From what I can see, and I'm not an expert at parsing code, our system should be ok based on 230.79 (A) or (B) since our PV system is one single branch circuit.

Since (A) does not mention how many wires in the circuit we might be more aligned with (B) which specifies "2-wire" circuits, which ours is as it is a 240V output.

NEC 230.79 (D) which they quoted as the relevant section says that "All Others" shall have a rating of not less than 60 amperes.

Are we a 2-wire branch circuit or are we an "Other"?

Thanks.
 
I think as long as your 30A disconnect is SUSE and rated for the available fault current then that ought to be okay. But I've run into this interpretation about the minimum 60A before, and I wonder how much it's worth fighting over. You can put 30A fuses in a 60A disconnect (you may need fuse reducers).
 
This one is really as old as grid tied PV. While you might find the occasional AHJ that will allow the (A) option almost all require the (D) option. It's so common it's not even worth asking about. Fuse reducers and a 30A fuse are the answer.
 
And we have installed #6 as is minimum conductor sized per 705.11(B)?
Appears service disconnecting means could be sized per 230.79.(A). If not ,whoops, I guess Plan Review has been missing something. I see this typical installation quite frequently on engineered drawings.
 
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