simple motor ocpd size?

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Toros

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Hi,
I am sizing the circuit breaker protection a sump pump motor which is 240v, 1-phase, 2-pole with 22 FLA.

Calculated so;

22A x 2.5 (per 430-52) = 55A
Chosen next size higher for standard..: 60A,2-pole circuit breaker , inverse time breaker.

Question is;
branch circuit feeding this motor should be based on 22A x 1.25%=27.5" rule , # 10 cu wire or,

#6 cu wire based on breaker size which is 60A now.???
 
Edwardtomas said:
Hi,
I am sizing the circuit breaker protection a sump pump motor which is 240v, 1-phase, 2-pole with 22 FLA.

Calculated so;

22A x 2.5 (per 430-52) = 55A
Chosen next size higher for standard..: 60A,2-pole circuit breaker , inverse time breaker.

Question is;
branch circuit feeding this motor should be based on 22A x 1.25%=27.5" rule , # 10 cu wire or,

#6 cu wire based on breaker size which is 60A now.???
Click to expand...
Compliance requires #10 Cu as the minimum. Conductor size is not based on the SC&GFP rating. However, there must be an appropriately-rated overload protection device in order to use the 250% SC&GFP rating.
 
ActionDave said:
What is the horsepower of the pump motor? High possibility there is thermal protection built into the motor. Highly unlikely you need #6 for conductors.
Click to expand...

templdl said:
These were my thoughts also. Double check if there is already thermal protection in the motor.
Click to expand...
I overlooked horsepower rating being a factor, so that is a good point. It may make the FLA (aka FLC) perhaps 28A if it's a 5HP motor.... 35A at 125%. #10 75?C or 90?C Cu would still be good provided terminal temperature limitation is 75?C. If only 60?C, minimum goes up to #8 Cu.

That said, not all sizing with respect to motors, especially motor-operated appliances, is based on horsepower and the respective value from the tables.
 
Just a couple thoughts:

Not sure where the HP rating is a factor. The OP noted the FLA hence it should be as good a saying xx HP. He basically saved the effort of having to look up the FLA which I am assuming he did (I did not check the tables). So assuming he did use the tables, the HP shouldn't be a factor.

The breaker at 2.5% is the maximum, it can be smaller than that.


The ground conductor is based on the overcurrent device. Not that it is a factor here because the ground does not need to be larger than the phase conductors, but it would require a ground based on the breaker rating.

Not sure where the thermal protection comes into play when sizing the breaker at 2.5%. Motors should all have some type of thermal protection or overload in them. The breaker is the fault device, not the overload protection device.
 
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