motor branch circuits #12 on 30 amp?

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lile001

lile001

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Midwest
We've got a discussion going about motor branch circuits. One guy maintains that #12 wire can never be used on a breaker over 20 amps, therefore the feeder for a 1 HP 115V motor must be #10, as this motor requires at least a 30A circuit breaker. Same issue for, say, a 15HP 460V 3 phase motor - it uses a 40A circuit breaker so a #10 would not be allowed.

THe other guy maintains that a motor branch feeder only needs to be 125% of the FLA, and the branch circuit breaker is irrelevant to the sizing of the wire. This would result in a 1HP 115V motor, with a 16 amp FLA, would be fine on a #12 wire.

Who is correct?
 
Re: motor branch circuits #12 on 30 amp?

See 240.4(D) and notice that it refers you to 240.4(G) for motors. You can put a #12 breakers up to (and probably higher than) 100 amps.
 
Re: motor branch circuits #12 on 30 amp?

The other guy is. See section 240.4(D). This section does not apply to the items in 240.4(E) through (G). (G) lists motor and motor-control circuit conductors. These circuits are sized and protected per section 430. Breakers and fuses for motor circuits are only used for short-circuit and ground-fault protection, overloading is protected by motor overloads, thus the conductor size can be smaller than the branch circuit breaker which is sized for faults and starting current.
 
Re: motor branch circuits #12 on 30 amp?

Is the rule of thumb about 20amp and 15 anp and 30 amp breakers and the 12,14,and 10awg wire just for residential and not for industrial? or eitherway,?
 
Re: motor branch circuits #12 on 30 amp?

The rule is in 240.4 (D) and coverers all installations "Unless specifically permitted in 240.4(E) through (G)" See the Code text.

there is a list of circumstances where conductors are installed and protected in such a way that causes this confusion.

Charlie
 
Re: motor branch circuits #12 on 30 amp?

I don't completely agree with these answers.You are only allowed to fuse #12 or #10 higher on a motor circuit if there is a thermal overload present in the motor or are going through overload heaters on a starter.
Is this the case? I don't Think you can fuse #12 wire at 30 amps for groundfault or short circuit protection just because it is a motor, unless it has a means of overload protection.
 
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