Since this is a resi. app. Can you use 4/0 SER from the Main to the sub panel?
so now we have a sub panel? regardless of the wiring method would not 310.15(B)(7) from 2011 NEC.
Handbook comment "section 310.15(B) (7) permitted the main feeder to a dwelling unit to be sized according to the conductor sizes in table 310.15(B) (7). the permission to use this table applies only to conductors carrying 100 percent of the dwelling unit's diversified load." Diversified load?
would the conductors now be required to sized to 310.15 (B) (16) ?
which would be250MCM AL?
what if the main panel is not located on the house and you are running feeders to the house you can derate the conductors and use table 310.15(B) (7)?
Gus has a very valid point and argument on this situation. But I would first ask, dose this meter comb have a built in buss for branch circuits or dose it just have the main?There has been much discussion to this Table during the last two or three Code cycles and there is still ambiguity in the enforcement.
A old lingering question has to do with some controversy concerning the reduced ampacity of SER in insulated areas.
Some inspectors rule the reduced ampacity conductor can not be used.
A second discussion has center around the situation where some of the load if fed from the service point ahead of the sub-panel. In those situations the sub-panel no longer carries 100% of the load. So you have a situation where an E/C feeds a 60 amp HVAC load from the interior panel and uses 310.15(B)(7) to feed that interior panel. On an identical job, he feeds the HVAC from a combo meter center thus reducing the sub-panel load by 60 amps but how he has to increase his feeder to the interior panel (unless he adds protection)...
There are different interpretations by AHJs
we're on the 2011 NEC so I think it's good to go.
310.15 B 7 will allow it. But if it were a situation where you used table 310.15 B 16 and it was in contact with thermal insulation it would drop it back to the 60 deg. column which would be 150 amp.It mostly depends on what temperature rating you are allowed to use for the SE cable, which is dependent on which edition of NEC applies.
If you are allowed to use 75C then 4/0 is acceptable either way. 310.15(B)(7) allows 4/0 for a 200 amp circuit, and as long as the calculated load is not over 180 amps 310.15(B)(16) also allows 4/0 because next size standard overcurrent device is 200 amps.