Please check me

[2571]

New piece of equipment coming soon, total amp draw will be 100 amps. Please check my figures.
100 amp x 1.25 = 125amp x .8 derating the wire = #2 THHN, #8 ground
100 amp x 2.5(inverse timed breaker)= breaker rated 250amps

using NEC 2002 430.52 for breaker calculations.

 

[jraef]

The breaker x 2.5 is a MAXIMUM size, not a recommended size. If you use that breaker, you must then size the wire for 250A x 125%. Also, I don't know where you got the .8 derating factor on the original wire size you did.

If this is for a dedicated motor branch circuit, the scenario is different by the way.

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[jraef]

D'oh!

Just noticed the reference to 430.52, which means it must be a motor branch circuit. In that case you can use the 250A CB as long as you have an overload relay in your motor controller.

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[LionelHutz]

If this is a single motor then the wire should be OK. You didn't specify a distance. The breaker should never need to be larger than 2X the motor FLA. I would use 150A or 175A.