Question on NEC 210.20
Question on NEC 210.20
(OP)
My question is regarding a branch breaker in a large 480v Power Panel. The circuit feeds a 36A heating load. Can a 40A breaker be used, knowing the following:
- This is at a small generating Station
- Space Heater is supposed to turn on only when ambient temperature is below 50F (10C)
- #8 AWG cable is rated for 90C, but rated for 50A (about 140% of load) at 75C insulation
Thanks!
- This is at a small generating Station
- Space Heater is supposed to turn on only when ambient temperature is below 50F (10C)
- #8 AWG cable is rated for 90C, but rated for 50A (about 140% of load) at 75C insulation
Thanks!






RE: Question on NEC 210.20
So conductors must be 125% of 36A or 45A. Yours are 50A, assuming you don't have to do any ambient temperature derating. No problem.
A 40A breaker protects a 50A conductor just fine. No problem.
What part of your design did you think was questionable?
Best to you,
Goober Dave
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RE: Question on NEC 210.20
RE: Question on NEC 210.20
Shouldn't the breaker also be sized to 125%, i.e. 45A(see 424.19)? Keeping 424.3(B) in mind, what does 220.51 apply to?
RE: Question on NEC 210.20
424.19 is for the disconnecting means, not the overload protection. It would apply if this breaker is also serving as the disconnect.
220.51 applies to feeders, not branch circuits. However, it does not conflict with 424.3(B). They both call for 100 percent load for fixed electric heating in calculations. That is, fixed electric heaters cannot be considered non-continuous loads.
And on MICHAELUSA's original question about 210.20, he is right and I am wrong
Best to you,
Goober Dave
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RE: Question on NEC 210.20
RE: Question on NEC 210.20
RE: Question on NEC 210.20