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Transformer primary wire sizing

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    Transformer primary wire sizing

    I have a 225kVA stepup xfmr 480V delta primary, 2,400V delta secondary that is connected to a 225kVA stepdown xfmr 2,400V delta primary, 480/277V wye secondary.

    If I use a 300A breaker for feeding the stepup transformer, can I size the primary conductors at 350kcmil?
    If this is the case, can the secondary conductors of the stepdown transformer also be sized at 350kcmil?

    The secondary of the stepdown transformer feeds a lighting distribution panelboard 480/277V with 400A main breaker.

    #2
    Yes to both sets of conductors, assuming that the secondary conductors are protected at their load end by a 300 amp OCPD.
    Don, Illinois
    (All code citations are 2017 unless otherwise noted)

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