220.82 optional load calc

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jaggedben

Senior Member
Location
Northern California
Occupation
Solar and Energy Storage Installer
Your opinions wanted...

Can the 220.82 optional load calc be used for a subpanel feeder that serves only a portion of a dwelling? Or is it only for service conductors and feeders that supply the entire dwelling? The language seems vague to me.

If the answer is that it's only for conductors supplying the entire dwelling, is it not strange that a subpanel feeder sized to 220 Part III might be required to be larger than the service conductors? Or is there something I'm missing?
 

wwhitney

Senior Member
Location
Berkeley, CA
Occupation
Retired
If the answer is that it's only for conductors supplying the entire dwelling, is it not strange that a subpanel feeder sized to 220 Part III might be required to be larger than the service conductors? Or is there something I'm missing?
(2020) 310.12(C) says that the feeder need not be larger (in ampacity) than than the service conductors with the 83% factor applied. Both it and the optional method 220.82 apply to a single family dwelling with a 3 wire single phase service, either 120/240 or 120/208.

As to the first question, I don't really know, but it reads to me as if the optional method can be used on feeders.

Cheers, Wayne
 
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