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Thread: Wire size, 3ph Delta, 120/240

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    Electrical Contractor/Instructor jwelectric's Avatar
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    Jun 2007
    North Carolina


    Quote Originally Posted by Rich B View Post
    Series High Delta 120/240 60 Hz 3 Phase power. My voltage reconnection chart tells me I could make that 139/277. I assume it too would have a "high" leg to neutral since it is the same wire configuration
    With a system of this voltage the high leg would be the square root of any line voltage squared minus the voltage from one end of the center tapped winding to the center tap squared when the system is not under any load. This would be the square root of 76729 minus 19321 or a high leg of 239.5 without load.

    This is also true for any high leg system like a 240/120 delta system. 240*240=57600, 120*120=14400. 57600-14400=43200. The square root of 43200= 207.84 and we round up to 208.
    Once under load the voltages will change on any system be it delta or wye depending on the load applied and the configuration of the load three phase or single phase.

    Also remember that the neutral of a wye system where nonlinear loads are served there can be no reduction of the neutral conductor due to the possibility of high harmonic currents on the neutral conductor.

    Edited the second time to add;

    The laws of physic are not up for debate. Math does not lie.

    If you are seeing 219V on the high leg to ground then the 120/240V nominal system is also high they would be 126 phase voltage and 252 line voltage.
    Last edited by jwelectric; 07-17-2012 at 11:58 AM. Reason: to correct math and add spacing

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