Wire Size

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eds

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200 amp main breaker panel with a 30 amp 2 pole installed for solar, my understanding of 705.12(2) will require 250 al for a residential application is this correct? NEC 2011
 
Depends...

Is this panel service equipment? ...i.e. the main breaker is the service disconnecting means.

If yes is the answer to my question, then not necessarily is the answer to yours because it hinges on 310.15(B)(7) being applicable and/or what your calculated load is.

If no to my question, yes is the answer to yours, barring omitted pertinent details.
 
Okay, thank you. Just over-thinking this some what, for what ever reasons I thought my wire would need to be based on the combined breaker rating. After a little thought I understand why it doesn't.
 
eds said:
200 amp main breaker panel with a 30 amp 2 pole installed for solar, my understanding of 705.12(2) will require 250 al for a residential application is this correct? NEC 2011
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Assuming ordinary conditions of use. Do a search on "conditions of use" if you are unsure.

Your 30A breaker, which is probably for a 5kW solar inverter, will require #10 Cu wire. Place this at the opposite end of the busbar from the 200A main, to comply with 705.12(D).

Your main breaker will require that which is ordinarily required for this building loads panel, whether or not the solar is present. Since the 205A of ampacity in 250 kcmil AL meets or exceeds the main breaker, the 250 kcmil AL wire is acceptable and conservative, as long as you do not need to upsize to curtail voltage drop.

There are other reasons why you would be able to use a smaller main wire:
1. If this is a service instead of a feeder
2. If you can take advantage of the "next size up rule", 240.4(B)
 
eds said:
200 amp main breaker panel with a 30 amp 2 pole installed for solar, my understanding of 705.12(2) will require 250 al for a residential application is this correct? NEC 2011
Click to expand...

I'm going to assume you mean 705.12(D)(2). As others correctly pointed out above, this section does not apply to service conductors.

It would take a really persnickety AHJ to require you to even consider the solar given that you have a main breaker panel. But even if they do, the solar has no effect in this case because it doesn't exceed 20% of the utility breaker. Your conductor just needs to be rated 200A, as normal.

Residential vs. commercial makes no difference in the 2011 Code, btw.
 
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