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Joined: Feb 2003
Posts: 198
Z
Member
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?


Shoot first, apologize later.....maybe
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Joined: Nov 2007
Posts: 764
K
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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.




Joined: Feb 2003
Posts: 198
Z
Member
We thougth it did not make sense either.
Your allowed to do it resi, but not commerial?
I will challenge the inspector,cuz I usually win anyway.


Shoot first, apologize later.....maybe
Joined: Jun 2006
Posts: 613
M
Member
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.


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