MOTOR STARTER BREAKER SIZING

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Jerry Albertelli

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If I have a three phase 480 VAC size three (3) starter in an MCC, and a 31.5 FLA 30 HP Motor connected to the size three starter, can the breaker that feeds the size three (3) starter be an 100 amp legally? If not, what code number in the NEC does it state that it has to be different?
 
The branch circuit breaker is sized to allow the motor to start, and it’s called motor short circuit and ground fault protection. Long duration events are protected by the overloads
Or
The breaker protects the wire
The overloads protect the motor
 
In this case I have an E3 plus for protection of the motor. However, if the E3 Plus were to fail, then the #6 wire that feeds the 31.5 amp motor would melt down. So. the top side of the starter is 100 amp and the bottom side is 31.5 amp protected by the E3 Plus (motor protection relay). That's what I was wanting to know is if the NEC supports this. Thanks for pour feed back...
 
Jerry Albertelli said:
In this case I have an E3 plus for protection of the motor. However, if the E3 Plus were to fail, then the #6 wire that feeds the 31.5 amp motor would melt down. So. the top side of the starter is 100 amp and the bottom side is 31.5 amp protected by the E3 Plus (motor protection relay). That's what I was wanting to know is if the NEC supports this. Thanks for pour feed back...
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I think you are going to lose the motor should the overload protection fail before you would have much chance of melting down the conductor, which can be 8 AWG BTW. If you have short circuit or ground fault conditions current will be high enough the 100 amp breaker trips before conductor gets that hot.
 
There are thousands upon thousand of installations similar to yours all allowed by the NEC. If you put in a breaker sized former the wire, the breaker would trip when the motor starts
 
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