National Electrical Installation Standards

Standards as High as Your Own

Friday, June 18, 2021


Good afternoon,

I read these questions and responses every day. Always seem to pick up valuable insight in the responses. Here is our question. If I have a box that has concentric knockouts in it (1/2-inch to 1 inch), and I only use the 1/2 inch KO, do I need to bond around the knockout, if the circuit is 277 volts, single phase?

Thanks in advance for your help.

TJ Owens 



Hi TJ, thanks for participating. Where concentric, eccentric, or oversized knockouts are encountered in circuits over 250 volts phase to ground, one of the bonding methods in Section 250.92(B)(2) through (4) must be applied to ensure the required continuity and conductivity, unless the box is listed for providing a reliable bonding connection, as stated in the exception.

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