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Transformer overcurrent protection on the primary.

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    Transformer overcurrent protection on the primary.

    We currently have two 120/208V UPS installations, each with a 480-120/208V transformer, and the transformers are individually connected to a 480v generator connection. This is just a temporary connection.

    For the permanent installation, the higher ups want to feed both transformers from one common circuit breaker on a 480V MCC.

    Is there anything in the code against feeding two transformers from one common circuit breaker?

    It's legal as long as you follow the guidelines in 4503(B)
    At my age, I'm accustomed to restaurants asking me to pay in advance, but now my bank has started sending me their calendar one month at a time.


      You might have trouble overcoming the inrush of the 2 transformers with a single CB


        Not common, but works.

        Use a 250% X FLA CB feeder, and the required full sized fat wire to each xfm.
        There is no next-size-up for the CB.
        The conductor ampacity has to meet or exceed the CB rating.

        Consider two fused disconnects - one per xfm. That could dump a lot of issues and allow a lot smaller primary conductors.
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