SolarPowered: That is exactly what I am saying. Feeder to an apartment, use 310.15(B)(6). Feeder to a swimming pool subpanel in a home, use 310.16. 310.15(B)(6) applies to services and feeders that supply power for _dwellings_, not anything else. We had a long discussion of this point here:
https://www.electrical-contractor.net/ubb/Forum2/HTML/001450.html It is my opinion that 310.15(B)(6) simply confuses the issue of proper conductor sizing. It seems to say that the ampacity of the conductors is different in this particular application. But it seems to me that what 310.15(B)(6) is really saying is that for a particular type of load (feeders to dwellings) a circuit which requires OCPD X and conductor ampacity Y, where Y is less than X.
This is done all the time for things like motors or welders, where the conductor ampacity might be half the OCPD trip rating. IMHO the service and feeder demand calculations should be modified to return _two_ numbers, one for required conductor ampacity, and the second number for OCPD rating. Doing the calculation on a dwelling might give a number such as 'this service requires an OCPD of 100A and a conductor ampacity of 80A', and the result would be a 100A main breaker and #4 conductors, matching what happens when 310.15(B)(6) is applied.
watthead: Based upon this last description, I agree that the feeder in question is the 'main power feed' of a dwelling and that 310.15(B)(6) applies. Sure sounds like the inspectors were looking for anything to hang a violation on, and I'm glad that you stuck with the appeal.
-Jon
