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Wednesday, March 30, 2016
Question:
We built a meter loop and from a 400 amp main disconnect, nipppled into a Nema 3 R gutter, then fed two 200 amp disconnects. At the 400 amp main disconnect we joined the grounded conductor to our grounding electrode system which consisted of a # 4 copper concrete encased electrode conductor, a # 6 copper rod electrode conductor, and a # 2 copper connected to the water service where it entered the building. The electrical inspector required us to again bond the grounded conductor to the gutter. With Article 90.4 of the N E C in mind, we complied. Your thoughts ?
Bobby Ross
A
Answer:
Hey Bobby thanks for your question. If I understand the installation you describe correctly it seems the inspector required you to create a NEC violation. If the 400 amp main disconnect is your service equipment, as defined in Article 100, the conductors on the load side (supplying the two 200 ampere disconnecting means) are feeders. A grounded conductor is not allowed to be connected to normally non-current carrying metal parts of equipment (the Type 3R wireway) on the load side of the service disconnecting means as stated in 250.24(A)(5). I'm confused about the 2 AWG copper grounding electrode conductor to the metal water pipe. If your service conductors are 500 kcmil copper, which are often used for a "400" ampere service, the grounding electrode conductor would need to be a 1/0 copper as stated in Table 250.66.