I need some help guys. I got into a friendly argument with an EC friend of mine about sizing subfeed conductors. House has 200a MB 40 space panel,adding 100a breaker to feed 100a MB panel in detached garage.I say the feeder wires must be sized using 310.16. He says you can use table 310.15(B)(6). Who eats the crow sandwich? Russell
Table 310.15(B)(6) Is for the service entrance conductors, service lateral conductors, and feeder conductors that serve as the main power feeder to a dwelling unit. A garage is not a dwelling!
Curt
Ok,this means that no subpanel fed from this 200a panel in the house could be fed with the reduced wire sizes in 310.15(b)(6). This includes subpanels inside the house itself, correct? Thanks for your replies! Russell
Have him read 310.15(6).
See if he still disagrees.
I,ve seen this mistake several times.
The easiest thing might be to install a smaller feeder breaker (80-90 amp?), if the load permits it.
When the code allowing downsizing the wiring to feed the dwelling unit was submitted, I believe the data used to support this was utility actual power usage from monthly meter readings. (Please correct me if I'm wrong on this anybody.)
Since the feed to garages is not metered and thus not included as part of the data, garages are not allowed to use this table, only the feed for the house.