what is the max overcurrent protection for a single motor

[iwire]

130617-1153 EDT

Dennis:

I was trying to get across the point that the main panel breaker was not protecting the motor. Something else has to do that, or the main panel breaker has to be designed to protect the motor and that is an unlikely situation as the original post was presented.

Thus, I tried to show that the motor was not protected by the main panel breaker by picking a load that would not likely stall the motor, but if no other protection was provided the motor would burn out.

.

The breaker protects the entire circuit, including the motor windings from short circuits and ground faults.

The motor overloads protect the entire circuit, including the motor windings from overload.

 

[david luchini]

The breaker protects the entire circuit, including the motor windings from short circuits and ground faults.

The motor overloads protect the entire circuit, including the motor windings from overload.

:thumbsup:

At the very least the breaker can't be more than values in 430.52, for any motor in the group which is 250% for inverse time circuit breakers. 9 x 2.5 = 22.5. Even a 25 amp breaker is too high.

Per 430.52, a 25A breaker would be the max allowable for a motor with an FLA of 9. And per 430.53(B), two 9A motors would be permitted on a 25A breaker.

 

[ritelec]

Thank you all !!!

 

[templdl]

The breaker protects the entire circuit, including the motor windings from short circuits and ground faults.

The motor overloads protect the entire circuit, including the motor windings from overload.

To my point. However, my intent is not to be nitpicking but you can't protect a motor winding from short circuiting as if they short circuit it is already a done deal. In the event a motor winding does short circuit of more likely should a winding go to ground the breaker trips to open the circuit to clear the fault in order to protect the upstream distribution system. This is similar to the breaker for the primary protection of a transformer.
Westinghouse developed the MCP to reduce the incidence of fires caused by a motor failure. The intent was to take the motor off line ASAP should a winding failure occur.

 

[don_resqcapt19]

...
I just went through this with an inspector. I had to feed each motor separately due to the critera not being met. One of which is, the two motors would have to be listed to be controlled by a single controller. ...

Can you cite a code section for this? I don't think that there is anything in the code that says anything like that.

 

[kwired]

:thumbsup:



Per 430.52, a 25A breaker would be the max allowable for a motor with an FLA of 9. And per 430.53(B), two 9A motors would be permitted on a 25A breaker.

My bad, exception 1 allows you to use next size up standard device, and I knew that, but somehow didn't remember when I needed to. Seems to happen more and more the older I get, and I'm not really that old yet.

 

[Little Bill]

Can you cite a code section for this? I don't think that there is anything in the code that says anything like that.

430.53(C)
That's what was cited by the inspector and also here when I posted about it. I'll have to (later) look up the thread