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Thread: ATS on transformer secondary

  1. #1
    Join Date
    Jun 2016
    Location
    Virginia
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    23

    ATS on transformer secondary

    This might be simple, but I don't recall encountering it before:

    Commercial/Industrial site. 480V service. Transformer down to 120/240V for the office area. They want a generator to back up the office only. Do I need to switch the neutral in the ATS?

  2. #2
    Join Date
    Mar 2011
    Posts
    115
    I could be wrong but I don't see why you would need to. I have inspectors that interpret things differently and while one will allow something another won't so it might not hurt to ask your local AHJ. I would think you could leave the neutral unswitched and as long as you don't bond the neutral and ground at the generator.

  3. #3
    Join Date
    Nov 2010
    Location
    Fort Collins, Colorado
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    2,724
    Quote Originally Posted by Electromatic View Post
    This might be simple, but I don't recall encountering it before:

    Commercial/Industrial site. 480V service. Transformer down to 120/240V for the office area. They want a generator to back up the office only. Do I need to switch the neutral in the ATS?
    Not as long as you set it up as a non-SDS, IE no neutral bond at the genset. The ATS will have to be after the Xformer OCPD, so if you already have a MB panel serving as the secondary protection you will have to rework it with a separate OCPD ahead of the ATS.

  4. #4
    Join Date
    Jun 2016
    Location
    Virginia
    Posts
    23
    Thanks!
    I was trying to think if the derived neutral and the neutral-ground bond at the transformer would create some kind of objectionable path for current getting back to the generator. I guess I was over-thinking it.

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