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    Xfrmr Size

    Approx what size xfrmr for 125a 480v panel on primary side and 120/208 60A panel on secondary side? Thanks.

    Sorry 50A 3P breaker feeding the transformer. I get 45kva.
    Last edited by mstrlucky74; 08-22-19, 11:11 AM.

    #2
    30kVA, and in reality you could make that a 100A panel on a 30kVA on the secondary side, but 60A CB is not a problem.

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      #3
      If you need 60 amps at 208 3phase to feed your load. 208 x 1.733 x 60= about 22kva or more.

      Using panel size or breaker sizes is not the best way to size it.
      John,

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        #4
        Originally posted by mstrlucky74 View Post
        Approx what size xfrmr for 125a 480v panel on primary side and 120/208 60A panel on secondary side? Thanks.

        Sorry 50A 3P breaker feeding the transformer. I get 45kva.
        If you're only trying to provide power to a 60A panel on secondary side
        30KVA transformer
        Primary side = rated max = 36A 480 3Ø, 50A/3p breaker for protection,
        Secondary side = rated max 83.3A available at 208 3Ø, 100A/3p protection

        You could always drop your secondary OCP to 60A/3p and call it a day.

        Comment


          #5
          Originally posted by S'mise View Post
          If you need 60 amps at 208 3phase to feed your load. 208 x 1.733 x 60= about 22kva or more,Using panel size or breaker sizes is not the best way to size it.
          I misunderstood that you were trying to figure out the size of an existing x former by looking at the 50a breaker feeding it.

          30kva would use a standard 40a breaker. You have a 50a.
          45kva would draw more than 50a breaker protecting it.

          Base on 480, 3 phase using a 50a breaker feeding the primary, it could be anywhere from 38 to 41kva.
          Although oversized for a 60a loaded secondary.
          John,

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