Sizing for1-20HP Motor

[wmeek]

I have a 20HP motor with a nameplate of 230V ,3phase, 47 amps. So to size the breaker feeding the motor, you use Table 430-250 for the amperage for 20hp, and mutiply times the values given in 430-52 (In this case we are using a breaker) of 250%. That would be 54A x 250% = 135A. So can I go down to a 125A breaker to feed this motor and be to code. Also the conductor size is based on 430-50 current values X 125% = 67.5a. So the conductor would need to be a #4. The motor is approx. 100' from the panel. So with all this said will this be code compliant for this motor installation.

 

[david luchini]

Yes, I would say that the #4 conductors and the 125A c/b would be compliant for the single 20HP, 230V motor.

I'd say the #4 conductors and a 150A c/b would also be compliant, for that motor.

 

[stew]

yes with the exception you can go to the next larger size breaker.which is the maximum size. 125 would be my choice however. wire size right dead on.

 

[Cow]

The easiest way is to always remember the nameplate is only for sizing overloads. Everything else comes the NEC tables. Sometimes the other guys forget that and try and size wire to the nameplate, etc.