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Thread: Three Phase Panel to Single Phase ATS

  1. #1
    Join Date
    Jun 2003
    Posts
    3

    Three Phase Panel to Single Phase ATS

    We have a customer with a 3-Phase 120/208V Main Panel. The want to hook-up a 12kW, 120/240V generator using a 120/240V automatic transfer switch. How would the branch circuit coming from the main panel be wired? What would be the volt/amp output?

  2. #2
    Join Date
    Feb 2003
    Location
    Seattle, WA
    Posts
    17,245

    Re: Three Phase Panel to Single Phase ATS

    OPTION 1:
    Step 1: De-energize, disconnect, and throw away the 120/208 panel.
    Step 2: Buy and install a 120/240 panel.
    Step 3: Follow the manufacturer’s instructions for the connections.

    OPTION 2:
    Step 1: Throw away the 120/240 generator.
    Step 2: Buy a 120/208 generator.
    Step 3: Follow the manufacturer’s instructions for the connections.

    (Please forgive the sarcastic tone. I haven’t finished my second pot of coffee yet.)

    The bottom line is that you are dealing with apples and oranges (or more precisely, apples and baseball bats). The two are not compatible.
    Charles E. Beck, P.E., Seattle
    Comments based on 2014 NEC unless otherwise noted.

  3. #3
    Join Date
    Feb 2003
    Posts
    3,172

    Re: Three Phase Panel to Single Phase ATS

    Is this 12 KW generator single phase?

  4. #4
    Join Date
    Feb 2003
    Posts
    898

    Re: Three Phase Panel to Single Phase ATS

    There is only one way to use this generator with this system, but I wouldn't recommend it, and it likely will not pass inspection.

    This hookup will work if all of the critical loads to be operated by the generator are 120 volt loads. The generator would be configured as a separately derived system.



    Ed

  5. #5
    Join Date
    May 2003
    Location
    Leesburg, VA
    Posts
    6,933

    Re: Three Phase Panel to Single Phase ATS

    Check the generator ouotput if the output is 12 wire, it is possible to reconnect this generator as 3 phase 4 wire 120/208 VAC.
    Brian John
    Leesburg, VA

  6. #6
    Join Date
    May 2003
    Location
    Leesburg, VA
    Posts
    6,933

    Re: Three Phase Panel to Single Phase ATS

    Why can't he install the generator as 120/208 single phase through the two pole ATS and to a new 120/240 VAC panel. Not the best situation and would avoid single phase 240 VAC loads, but it would work. You would have to adjust the normal sensing realys in the ATS. Not the best installation for sure........... Check on the twelve wire winding.
    Brian John
    Leesburg, VA

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