My friend, who I work with on weekends, plus all my other work,had a plan review with our local inspector this past week. He,I, will be wiring a new addition to a gated community, community building, with M/C cable. Plans call for electric baseboard heaters, but inspector says we can not put 3750 watts of heat on a #12-20A circuit anymore, in a commerial area, only 3000 watts max on 20A & 5000 watts max for a 30A circuit. Is this true?
I think I would politely ask the inspector how he came up with those numbers. Unless he’s applying some derating or other correction factors, I just can’t figure it. The only NEC 2008 change for fixed electric space heating equipment is 424.19, regarding disconnecting means being rated for 125% of the total load. Again, this requirement is for the total load, not the branch circuit rating. He may be taking the 3750-Watt heater load and dividing it by 125% to get his 3000-Watt limit. If so, that’s not the correct way to do it. The branch circuits are considered continuous loads, so can only be loaded to 80%. Such as 20A X 240V X 80% = 3840W or 3328W if it’s 208V. That would be a 16A load. 16A X 125% = 20A rated disconnecting means. Most DPST line-voltage thermostats have a 22 Amp load rating, so the 125% requirement for the disconnecting means is already met. Other than that, I’m at a loss to explain.
The Canadian Electrical code would allow #12 feeding base board heater to be loaded to the full 20 amps or 4800 watts on a 25 amp or 30 amp breaker depending on the availability from a manufacturer for a 25 amp breaker. #14 can be loaded to 3600 watts on a 20 amp breaker. This is one of the very few places where a wire can be loaded to its full rating and only applies to baseboard heaters. I know this is an NEC question except that unification of our respective codes is supposed to be a mutual objective.