National Electrical Installation Standards

Standards as High as Your Own

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Friday, July 19, 2019

Question:

Hello all, I have a new storage building at a local high school being fed from an existing panel in the school. The engineer had me pull a grounding conductor in with the feeders, but my inspector is saying I need to bond my neutral at the disconnect for the new building.... my take is that the neutral is already bonded at the main switchgear for the school and bonding the neutral again would cause the grounding conductor to be a parallel run with the neutral back to the panel the building is fed from (not the switchgear). For this on whether or not the neutral should be bonded at the new building and if so, should I eliminate the ground I pulled in with the feeders...

Fyi the service is  225A 480/277V 3 phase 4 wire, not that that should change anything.

Thank you,

Jeremy Buxman
A

Answer:

Hey Jeremy thanks for your question. An equipment grounding conductor you installed is required as stated in the first sentence of 250.32(B)(1). The last sentence of 250.32(B)(1) prohibits connecting a grounded conductor (neutral conductor in your example) to the equipment grounding conductor. Connecting the grounded conductor to the equipment grounding conductor would create a parallel path for normal current as you mention and also violate 250.24(A)(5). Show those sections to your inspector.

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