motor circuit equipment grounding conductor

[cwain]

Since the equipment grounding conductor is based on the size of overcurrent protection device. Lets say the inverse time breaker on a 30 amp FLA continuous load motor is 30x 250% = 75 amp so we will use a 80 OCP.
circuit ampacity would be 30 x 125%= 37.5 so we will use # 8 wire size.

My question is do I size the equipment grounding conductor 40 amps(#10) from table 250.122 or 80 amp (#8 ) from same table?

 

[augie47]

Neither
See 250.122(D)
(sized by the equivalent DE fuse)

 

[cwain]

Neither
See 250.122(D)
(sized by the equivalent DE fuse)

thanks , that was right in front of my eyes and I didnt see it.

 

[don_resqcapt19]

Neither
See 250.122(D)
(sized by the equivalent DE fuse)

Gus,
I don't agree completely with this. 250.122(D) is the correct section, but in this case we must apply 250.122(D)(1). Your answer suggests that we should apply 250.122(D)(2). (D)(2) only applies when the branch circuit short circuit and ground fault protective device is an instantaneous trip breaker or motor circuit protector. That is not the case here as we have an inverse time breaker. The EGC is sized based on the 80 amp breaker and will require a #8 EGC.

If the breaker was an instantaneous trip device, then the EGC would be sized on the maximum permitted dual element fuse...in this case a 60 amp fuse and we would only need a #10 EGC.

 

[augie47]

Thank you, Don.
I stand corrected. I misread the OP. I see very few Instantaneous Trip and sometimes when I read "Inverse Time" my mind plays tricks. Hopefully cwain will return to the post.

 

[yired29]

Neither
See 250.122(D)
(sized by the equivalent DE fuse)

250.122 A (in no case shall they be required to be larger than the circuit conductors supplying the equipment.)

This would also apply to motor circuits as well. Although not in this case with #8 circuit conductors.