Equipment Ground not required to be larger

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I cannot seemed to find it in the code, but was there an exception where the egc was NOT required to be larger than the circuit conductors for motors, or other circuits???

Seeing how the short circuit ground fault device can be larger than the ampacity of the conductors, and normally you would size off of that. For example, 100 amp scgfd with #8 conductors feeding a motor, would you have to go to #6 for the egc, or can you use #8 since the circuit conductors are #8?
 

david luchini

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See 250.122(A). That is what you are looking for.

Although, I'm not sure if 250.122(D)(1) means for motor circuits specifically, it must be based on the OCPD size.
 
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Cow

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I cannot seemed to find it in the code, but was there an exception where the egc was NOT required to be larger than the circuit conductors for motors, or other circuits???

Seeing how the short circuit ground fault device can be larger than the ampacity of the conductors, and normally you would size off of that. For example, 100 amp scgfd with #8 conductors feeding a motor, would you have to go to #6 for the egc, or can you use #8 since the circuit conductors are #8?

A 100 amp OCPD only requires a #8 ground, why would you need #6?

I'd say 250.122(A) is the one.
 
Thanks for the response, I had read 250.122(A) and had overlooked it somehow!! I knew it was in there, just forgot where. But thats the one. This had come up when I was explaining motors to a fellow electrician.

There was a #12 wire that was comming off of a 30 amp breaker, he thought you still needed #10 ground. I said no, the 250.122(D)(1),(2) is overiden by 250.122(A). Even though the short circuit and groundfault device is higher than the ampacity of the #12 and that section requires you to size it according to the that device, you can never have more current than a #12 can handle. ;)

Thanks again. Maybe a proposal should say something to effect that 250.122(A) superseedes the rest of the articles. ;)
 

hurk27

Senior Member
Thanks for the response, I had read 250.122(A) and had overlooked it somehow!! I knew it was in there, just forgot where. But thats the one. This had come up when I was explaining motors to a fellow electrician.

There was a #12 wire that was coming off of a 30 amp breaker, he thought you still needed #10 ground. I said no, the 250.122(D)(1),(2) is overridden by 250.122(A). Even though the short circuit and ground fault device is higher than the ampacity of the #12 and that section requires you to size it according to the that device, you can never have more current than a #12 can handle. ;) Thanks again. Maybe a proposal should say something to effect that 250.122(A) supersedes the rest of the articles. ;)

While this is partly true, in a ground fault the available fault current will be much higher that the #12 can handle if it was for a long duration, but it is so high that the breaker acts so fast to clear the fault that the conductor doesn't have time to heat up and cause damage to it.

But this can turn around in long runs, and since the resistance of a long run will limit the available current, it can act in the opposite way and cause the breaker to take a much longer time to open thus damaging the conductors even though there is less amps.
 
While this is partly true, in a ground fault the available fault current will be much higher that the #12 can handle if it was for a long duration, but it is so high that the breaker acts so fast to clear the fault that the conductor doesn't have time to heat up and cause damage to it.

But this can turn around in long runs, and since the resistance of a long run will limit the available current, it can act in the opposite way and cause the breaker to take a much longer time to open thus damaging the conductors even though there is less amps.

Such the reason for the 'recommendation' for using 3% voltage drop compensation. ;) Thats why we upsize the wire.
 
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