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Thread: Grounding Electrode for Transformers

  1. #1
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    Grounding Electrode for Transformers

    I am working at a large machine shop that has transformers for all the industrial equipment. The electrical work was all performed by an electrical contractor. I noticed that all the transformers (over 30 of them) have been bonded to the water line through out the facility, but I do not see any grounded electrodes installed anywhere. Many of these have passed inspection, but I am curious because I did not think the water line could be used as a grounding electrode unless it was within 5 feet of the entrance to the building. Most of the connections are from over 200ft from the entrance. Am I missing something in the code?

  2. #2
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    Quote Originally Posted by wilder2188 View Post
    I noticed that all the transformers (over 30 of them) have been bonded to the water line through out the facility, but I do not see any grounded electrodes installed anywhere.
    They don't need individual grounding electrodes but they do need an EGC to the overall grounding system. This could be the conduit holding the supply feeder.

    Quote Originally Posted by wilder2188 View Post
    Many of these have passed inspection, but I am curious because I did not think the water line could be used as a grounding electrode unless it was within 5 feet of the entrance to the building. Most of the connections are from over 200ft from the entrance.
    When the water line is used as a grounding electrode, you're required to connect the GEC within 5' of it entering the building (250.52). That has nothing to do with proper grounds at the transformers. (250.30, 250.66)

    All that said, see 250.52(a)(1):

    Exception: In industrial, commercial, and institutional buildings or structures where conditions of maintenance and supervision ensure that only qualified persons service the installation, interior metal water piping located more than 1.52 m (5 ft) from the point of entrance to the building shall be permitted as a part of the grounding electrode system or as a conductor to interconnect electrodes that are part of the grounding electrode system, provided that the entire length, other than short sections passing perpendicularly through walls, floors, or ceilings, of the interior metal water pipe that is being used for the conductor is exposed.

    I don't think that allows the water line to be used as the GEC for the transformers, however.

  3. #3
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    Take a look at 250.30(A)(7) {'08}
    The water line may well be the suitable grounding electrode for the transformer secondary.
    At my age, I'm accustomed to restaurants asking me to pay in advance, but now my bank has started sending me their calendar one month at a time.

  4. #4
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    Thank you. That answered my question.

  5. #5
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    Quote Originally Posted by zbang View Post
    They don't need individual grounding electrodes but they do need an EGC to the overall grounding system. This could be the conduit holding the supply feeder.
    250.30(A) requires that transformers have a GEC connected to a grounding electrode system.

    The EGC cannot serve this purpose.

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