National Electrical Installation Standards

Standards as High as Your Own

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Friday, January 18, 2019

Question:

Re: CQD answer published Thursday, January 10, 2018 - Continuous Loads

I'd like to just comment on the CB or OCPD rating of the feeder. The ampacity is determined by the method described, 125% of the anticipated full load. The OCPD then can be selected base on that. For feeders, the standard size value for OCPD can be rounded down from that ampacity rating, not up as required for branch circuits.

Best regards, Nick Abbatiello

A

Answer:

Hey Nick thanks for you comment. You are correct the feeder must be sized to have an ampacity at least (minimum) 125% of the load, if it is a continuous load, as stated in 215.2(A)(1)(a). The overcurrent device must also be sized to at least 125% of a continuous load as stated in 215.3. You might be able to round down from the conductor ampacity but it cannot be rated less than 125% of the load, whether or not it is a standard size. These rules are the same for branch circuits in 210.19 and 210.20.

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