200A meter/main feedthrough to dwelling

E

Errl

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Location
Colorado
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Electrician
I have a job relocating an overhead service to a livable garage. I have a 200A meter main with a feed through that is going to be set on the garage (overhead mast with a set of 4/0AL). Garage will be fed with a 100A sub panel and the house will be connected to the feed through lugs via underground conduit. The existing service on the house will be converted to a 200A sub panel with a main breaker. My question is does the wiring from the feed through panel to the house sub panel have to be larger than the 4/0AL feeding the service? Would I be required to upsize the feeders to the house to 250AL? Would this meet 310.12 since the house is a dwelling separate from the ADU?

Also the panel on the house has a 40A solar back feed. Since solar would be considered a power source and not a typical load would it still fall under 310.12 since the solar could potentially back feed the panel at the ADU?
 
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Should not be a problem. What is the calculated load of the house? What is the calculated load of the garage/ADU? If all that fits in the 200A service, there should be little risk of overload anywhere. Even if the house calculates to 180A, 4/0 AL is good for that before 83% factor is applied. Since the house is a dwelling, you have even more margin since the 83% rule applies. Don't see solar affecting it either if the solar backfeed is at the opposite end of the 200A panel. Even better if the 200A panel actually has a 225A bus, but that isn't required.
 
well, the dwelling feeder derating factor would require the house be detached from the garage. if it's not, then that feeder doesn't qualify for the 83% derating, as it's not the 'entire dwelling unit load'.

then again, you should be good even without that dwelling feeder derating. 4/0 alum is good for 180a. you're allowed to round up your OCPD under 240.4(B), and those conductors can be protected by a 200a breaker. granted, it's only technically rated as a "180a feeder," but it's protected by a 200a OCPD.
 
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