Electric Duct Heater Breaker and Wire Size

[Deezy]

Hi everybody, we are connecting power to an electric duct heater. 480 volts, 3 hots and a ground with an FLA of 180 amps. Using the 100 amp or over rule for terminal degree ratings, i'd use the 75 degree column which puts me at 200 amps with 3/0's. Sizing the breaker to 125% of the load puts the breaker size at 225 amps. I believe that this is properly sized per the NEC but a colleague of mine believes that 4/0's should be used. I think we meet all the conditions of 240.3 (B) to use the next standard breaker size up above the ampacity of the conductor being protected. I'd love to hear your opinions on the matter.

 

[david luchini]

4/0 is correct.

You don't meet the 240.4(B) requirement.

Also, your conductors need an amapcity of 225A per 210.19. 3/0 isn't large enough.

 

[infinity]

200 amps is a standard size so you cannot go up to a 225 amp OCPD with a 200 amp conductor. As David stated also you need a 225 amp conductor.