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Thread: Grounding for generators in parallel

  1. #1
    Join Date
    Jun 2007
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    Grounding for generators in parallel

    We have (3) outdoor gas turbine generators (480v/3ph, 1MW each)
    power a 480v/3ph parallel switchgear also sits outside.

    The switchgear is then feeds a step up 480v:5KV transformer,
    the output of xfmr connect to an existing underground 5KV feeder
    at one end, the other end of this 5KV feeder is powered from utility
    as backup source via a MV switch (note: this 5KV feeder feeds
    several buildings in the area)

    Question: Does nec require to ground the parallel switchgear
    above? i.e bond neutral to equipment ground bus
    and then connnect to the ground rod, maybe?

    All turbine generarors were grounded via a ground wire connect all
    generarors and binddto a triad ground rods.

  2. #2
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    There is a lot of detail missing and I think without a oneline showing where all the N-G bonds and grounds, grounding electrode conductors and grounding electrodes are, an incomplete answer will be given.

    Can you describe or draw this?
    Ron

  3. #3
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    And please use the NEC terms instead of the generic "ground", on a drawing or description. Are these generators separately derived?
    Moderator-Washington State
    Ancora Imparo

  4. #4
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    Quote Originally Posted by ron View Post
    There is a lot of detail missing and I think without a oneline showing where all the N-G bonds and grounds, grounding electrode conductors and grounding electrodes are, an incomplete answer will be given.

    Can you describe or draw this?

    See attached.
    Attached Images Attached Images

  5. #5
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    Since the Gens have N-G bonds, then a N-G bond is not installed at the parallel gear.

    The middle gen should be routed to the grounding electrodes directly.

    I am surprised that it is 4W+G from the gens to the parallel gear. Typically I would think it is 3W+G, not 4W+G since there is a N-G bond at the gens. Who needs to waste the extra conductors.
    Ron

  6. #6
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    Jun 2007
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    Quote Originally Posted by ron View Post
    Since the Gens have N-G bonds, then a N-G bond is not installed at the parallel gear.

    The middle gen should be routed to the grounding electrodes directly.

    I am surprised that it is 4W+G from the gens to the parallel gear. Typically I would think it is 3W+G, not 4W+G since there is a N-G bond at the gens. Who needs to waste the extra conductors.
    Can we not ground the middle generator
    as you wrote?

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