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Thread: Disconnect fusing

  1. #1
    Join Date
    Nov 2007
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    915

    Disconnect fusing

    Is it a violation to fuse one pole of a 3 phase supply at a different amperage?If yes, could you please direct me to the pertinent code that would apply.

    Thanks

  2. #2
    Join Date
    Jul 2006
    Location
    San Francisco Bay Area, CA, USA
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    Quote Originally Posted by nizak View Post
    Is it a violation to fuse one pole of a 3 phase supply at a different amperage?If yes, could you please direct me to the pertinent code that would apply.

    Thanks
    Some detail would be helpful.

    Are you feeding separate single phase loads? If so, and you have sized the disconnect for the highest load, sized the conductors appropriately, and you are OK with disconnecting all loads if needing to disconnect one of them, then there is no code issue I can think of.

    If feeding a three phase plus a single phase from the same switch, I think it could be done if you paid enough attention to all of the details such as properly sizing the disconnect and ensuring that the lugs are rated for more than one conductor, and that the fuse sizes fit within the rules for both loads, but I think all of that will be highly unlikely.

    If feeding just a three phase load, I don’t see the validity of even considering it.
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  3. #3
    Join Date
    Oct 2009
    Location
    Austin, TX, USA
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    10,026
    Quote Originally Posted by nizak View Post
    Is it a violation to fuse one pole of a 3 phase supply at a different amperage?If yes, could you please direct me to the pertinent code that would apply.

    Thanks
    I see it done in 240V high leg services, where the B phase fuse is smaller than the A and C phase fuses.

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