Two motor feeder CB size

[olc]

Circuit breaker size for a feeder for a duplex pump controller:
250% of one motor plus FLC for the other motor.
Am I reading 430.62 correctly?
So for two 20HP, 460V motors, the feeder circuit breaker can be up to 94A?

 

[david luchini]

That's not quite correct. Its not 250% of the largest motor plus the fla of the other motor, its (not to exceed) the largest rating or setting of an OCP for the largest motor plus the fla of the other motor.

For instance, if you had one 20HP and one 7.5HP, 460V motors, the method you describe would allow:

2.5*27+11=78.5A, or a 70A OCPD.

430.62 allows:

2.5*27=67.5A or a 70A OCPD (next standard size up)

70+11=81A, or an 80A OCPD.

Your two 20HP motors would be allowed on a 90A feeder OCPD.

 

[augie47]

Note that is for feeder protection. Each motor would still need individual protection.