National Electrical Installation Standards

Standards as High as Your Own

Thursday, December 15, 2016


We are removing a 4000 amp 120/208 volt 3 phase bus that runs horizontal in a ceiling, and installing 11 - 4" pvc pipes in the ground with parallel 500 mcm wires. These pipes are after the main service disconnect feeding a MCC. Do I need to pull a 500 mcm ground in each pipe to satisfy 250-122 (F)?




Hey Mike thanks for your question. Yes, the equipment grounding conductors in each raceway need to be sized based on the overcurrent device protecting all of the parallel conductors as stated in 250.122(F). For a 4000 ampere overcurrent device a 500 kcmil copper equipment grounding conductor needs to be installed in each raceway as shown in Table 250.122.


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