Local Motor Disconnect Size

[Artemis]

If a motor is protected by a circuit breaker, does the local non fused disconnecting means need to have an ampacity rating equal or larger than the circuit breaker? If not, what code reference covers this?

 

[raider1]

Check out 430.110 for the ampere rating and interrupting capacity of the required disconnecting means.

Chris

 

[richwaskowitz]

Use the HP rating

Use the HP rating

Does the disconnect you are using have a horsepower rating? For example, there are times when a 30 amp disconnect, which has a 20 HP rating is used in a motor circuit which is protected by a fuse over 30 amps. Case in point, a 20 HP motor with an FLA of 27 amps at 480 volts 3 phase and has a 45 amp fuse in the circuit, yet the "30 amp" switch has a rating of 20 HP.

 

[mull982]

I believe you also must factor in the Locked Rotor Current rating of the motor as indicated in 430.110(c)(2) when combined with other loads for determining the disconnects hp rating. Althogh I'm not sure exactly how this works.