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Thread: 120/208y - 480 delta

  1. #1
    Join Date
    Feb 2004
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    19

    120/208y - 480 delta

    is there any way to get a neutral when going from 120/208Y to 480 delta. The wrong transformer was ordered and someone asked if we could just use the same neutral from the primary side for the secondary. I didn't think so but figured I would check here.

  2. #2
    Join Date
    Feb 2003
    Location
    Portage, Indiana NEC: 2008
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    9,911

    Re: 120/208y - 480 delta

    No as the primary side is isolated from the secondary. you must use a "Y" secondary. the transformer sounds like a step down type?
    Wayne A. From: N.W.Indiana
    Be Fair, Be Safe
    Just don't be fairly safe

  3. #3
    Join Date
    Apr 2003
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    5,156

    Re: 120/208y - 480 delta

    I agree with Wayne in that "No".

    A neutral is created by the "Y" configuration of a three phase transformer.

    I would attempt to get the transformer exchanged for the correct one. The suppliers I deal with will work with me on just about anything.

    And Don't you have to ground the secondary?
    Sam, San Francisco Bay Area

  4. #4
    Join Date
    Feb 2003
    Location
    Seattle, WA
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    17,245

    Re: 120/208y - 480 delta

    The neutral of a transformer for which the line-to-line voltage is 480 volts will give you a single phase voltage (line-to-neutral) of 277 volts. That 277 is what is needed in your situation, and it cannot be derived from a delta configuration. Tell them to send it back and give you the right transformer.
    Charles E. Beck, P.E., Seattle
    Comments based on 2014 NEC unless otherwise noted.

  5. #5
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    Feb 2004
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    19

    Re: 120/208y - 480 delta

    Thanks guys, I appreciate the responses.

  6. #6
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    Jan 2005
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    Southeast Texas
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    Re: 120/208y - 480 delta

    Coincidentally, on Friday I got a call from a former student asking about the opposite situation. They were needing a normal step-down 480 delta to 120/208 wye xfmr. But the supply house had sent out a 208 to 480 step-up xfmr. He asked if they could just hook it up with the 480 as primary and get the 120/208 from the other side. My first reaction was "yes" but I got him to draw the nameplate and fax it to me.

    The primary was a 208 volt delta and the secondary was 480/277 wye. So, he could not use the xfmr "backwards" to derive 120/208.

    A 208 delta to 480/277 wye is exactly what is needed in the case in question of this thread.
    IBEW LU 716

  7. #7
    Join Date
    Aug 2004
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    11,834

    Re: 120/208y - 480 delta

    can't you create a neutral with a zig-zag xfmr?
    Bob

  8. #8
    Join Date
    Apr 2003
    Posts
    5,156

    Re: 120/208y - 480 delta

    What is a zig-zag transformer?
    Sam, San Francisco Bay Area

  9. #9
    Join Date
    Feb 2003
    Location
    Massachusetts
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    49,520

    Re: 120/208y - 480 delta

    Originally posted by physis:
    What is a zig-zag transformer?
    A Zig and a Zag

  10. #10
    Join Date
    Apr 2003
    Posts
    5,156

    Re: 120/208y - 480 delta

    Aren't those all "Y"s?
    Sam, San Francisco Bay Area

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