2020 NEC 310.12(C), feeder not supplying all loads?

[Ricko1980]

I have an easy clarification question for someone. I'm looking at what's been renumbered to 310.12(C) in the 2020 NEC. Do I understand correctly in that this is intended to limit the conductor size for subpanels, or other situations where a feeder doesn't serve all loads?

For example, suppose an apartment has a main panel in the common garage area with a service rating of 125A, the conductors from the meter to the main panel can be #2CU per 310.12(A).

But now suppose there's a single receptacle under that main panel, and all the rest of the loads are served by a subpanel in the apartment. Is 310.12(C) intended to allow us to size the feeder for the subpanel also at #2CU, such that it's not larger than the feeder to the main panel, rather than having to upsize it to #1 just because the subpanel "doesn't serve all loads"?

Clarification appreciated,

Ricko

 

[don_resqcapt19]

Yes, in that application, since the feeder supplies the total load of the individual dwelling unit, the 83% sized conductors are permitted.
Note that this is not a change for the 2020 code. This was permitted by 310.15(7)(3) in 2017.

 

[Ricko1980]

Thanks, don_resqcapt19. Meanwhile, I found another mikeholt post on the old NEC numbering, and realize I should have searched for that first. Thanks!