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Thread: Grounding Seperately Derived System

  1. #1
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    Grounding Seperately Derived System

    An industrial facility has installed an additional 12470V Delta-480V Wye transformer and secondary switchgear. The transformer and gear are BOTH located outside. A system bonding jumper is installed at both the transformer and secondary switchgear. Per 250.30(A)(1) exception 2, this is allowed if parallel paths for the grounded conductor are not created. PVC conduit was utilized between the transformer and switchgear. So far I believe this is NEC compliant. Where I believe it begins to very, is the location of the grounding electrode connection. The current installation has this connection at the switchgear instead of at the transformer. Per 250.30(C), this connection shall be made at the source for an outdoor separately derived system. Since both the transformer and switchgear are outside, does this present a problem? Should the grounding electrode connection be moved to the transformer? Should an additional grounding electrode connection be made at the transformer as well? If a grounding electrode connection is made at both locations on a common GES, would parallel paths come into play?

    Thanks

  2. #2
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    Why are there two system bonding jumpers? Typically the GEC goes to the equipment where the SBJ or the MBJ is installed.
    Rob

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    All responses based on the 2014 NEC unless otherwise noted

  3. #3
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    Rob,

    I imagine that one came installed within the transformer and the contractor installed another at the first disconnect means. Additionally, a supply-side bonding jumper was not installed between enclosures since 250.30(A)(1) exception 2 was followed. I am not saying this is best practice but appears to be compliant. I am assuming that 250.30(C) was added as a similarity to 250.24(A)(2) to keep the grounding electrode connection outside of the building. Since this particular installation involves having the transformer and disconnect outdoors, I am thinking that the intentions of this section would be met since the grounding electrode connection is outdoors (just not at the transformer)?

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