Parallel Motor feeders

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citcapp

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Article 250.112 requires that in parallel runs the grounds must be sized to the overcurrent protection. This I understand. But when it comes to motors I am finding confusion among engineers and inspectors on using this along with Article 430.52 Exception #1. In researching several engineered prints and talking to Engineers I have found they all use the size of the running load of the motor to determine the feeder size the calculate the ground based on the conduction size (example 400 amps parallel 250 KCM cu with a #2 ground.) then use Exception #1 to set the trip rating @ 500 amps. I am finding the the inspectors are running a 50-50 split on agreement and disagreement. What is the correct answer to this question?

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Pat
 
Pat,
The size of the EGC for a motor must be based on the size of the OCPD and not the motor overload protection. There was a change in this rule for the 2008 code. Under the 2005 code the EGC was required to be sized based on Table 250.122 and the rating of the OCPD, except where the OCPD was an instantaneous trip device and in that case and that case only the EGC was sized based on the rating of the motor overload device.
In the 2008 code if the OCPD is not an instantaneous trip device the EGC is sized on the rating of the OCPD, but if it is an instantaneous trip device then the EGC is sized based on the maximum size dual element fuse that would be permitted per 430.52(C)(1) exception #1.
 
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