resizing motor ground

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don_resqcapt19

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I must be missing something in this logic. If the EGC is appropriately sized for the motor load conductors, then the motor is downsized, the EGC is already adequately sized, even though the phase conductors are now larger than are required for the smaller motor.

If the EGC was sized originally based on the correct size phase conductors for the smaller motor, then the phase conductors were upsized to account for voltage drop, I would agree now that the EGC would have to be upsized also.
Under the current code, the ungrounded conductors that were the correct size for the larger motor and the larger OCPD. Now with the smaller motor and smaller OCPD, the ungrounded conductors are larger than the minimum size that would be permitted to serve that motor. The fact that the ungrounded conductors are larger than the minimum size that would be permitted triggers the rule in 250.122(B) and will require an increased EGC.

250.122(B) applies any time that the ungrounded conductors are larger than the minimum size that is permitted by the code. It does not just apply where the ungrounded conductors have been increased in size to account for voltage drop. That was the rule 3 or 4 code cycles ago, and will be the rule in the 2017 code, but is not the rule now.
 

mjmike

Senior Member
Under the current code, the ungrounded conductors that were the correct size for the larger motor and the larger OCPD. Now with the smaller motor and smaller OCPD, the ungrounded conductors are larger than the minimum size that would be permitted to serve that motor. The fact that the ungrounded conductors are larger than the minimum size that would be permitted triggers the rule in 250.122(B) and will require an increased EGC.

250.122(B) applies any time that the ungrounded conductors are larger than the minimum size that is permitted by the code. It does not just apply where the ungrounded conductors have been increased in size to account for voltage drop. That was the rule 3 or 4 code cycles ago, and will be the rule in the 2017 code, but is not the rule now.

don_resqcapt19 nailed it. He fully understands what I am talking about.
 

don_resqcapt19

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...
250.122(B) applies any time that the ungrounded conductors are larger than the minimum size that is permitted by the code. It does not just apply where the ungrounded conductors have been increased in size to account for voltage drop. That was the rule 3 or 4 code cycles ago, and will be the rule in the 2017 code, but is not the rule now.
Note action on motion 70-7 at the annual meeting resulted in the change that had been accepted in the second draft being rejected.

The previously accepted change would have made this rule apply only where the conductors had been increased because of voltage drop.

The action on the motion, keeps the 2104 wording of 250.122(B) for the 2017 code.
 
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