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Thread: Multiple Seperately Derived Systems

  1. #1
    Join Date
    Nov 2014
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    Multiple Seperately Derived Systems

    My facility is served by 480 VAC wye-connected 1200 Ampere 3 Phase. We have 480 to 240 3 phase delta-delta transformers serving vessel heating units. I am contemplating grounding phase B and wondering what issues may arise

  2. #2
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    Right now the secondary is not "grounded" at all? The general answer is that nothing will happen, although you'll need to remove any fuses in the now-grounded lead (3 pole breakers would be OK).

  3. #3
    Join Date
    Nov 2014
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    Quote Originally Posted by zbang View Post
    Right now the secondary is not "grounded" at all? The general answer is that nothing will happen, although you'll need to remove any fuses in the now-grounded lead (3 pole breakers would be OK).
    Correct, secondary is ungrounded. I cannot think of any scenarios this would cause an issue, but don't know for certain.

  4. #4
    Join Date
    Nov 2015
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    Corner grounded deltas were widely used at one time, not so much anymore. How big a change it makes in your system depends on your system. The grounded phase now will have to be treated as a grounded conductor and meet NEC requirements. One thing that means is that it has to be remarked everywhere it is visible as a grounded conductor. Fuses can't be used as OCPD unless tripping the fuse in the grounded leg opens the other two legs. If you have any ground fault monitoring, which you should, you will have to take that out. You will have to go through NEC art. 250 and make sure you can comply. Make sure it's worth it if you have a functioning ungrounded system. No reason to poke the bear.

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