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Thread: Accidental intersystem bond - okay?

  1. #1
    Join Date
    Aug 2017
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    Accidental intersystem bond - okay?

    Inspecting work on a large medical campus and ran into this situation, seems wrong to me, but can't really prove or disprove that notion. Attached a sketch for clarity. Basically, we have a 480V 800A emergency generator electrical service in EMT passing from one building through another to a third building. In between, these newly installed 480V conduits make contact with the low voltage fire alarm system EMT conduits in the middle building. I took exception, and the contractor took exception to my exception .

    Researching on topics such as intersystem bonding, etc., I don't know whether:

    1. formalize a bond between the systems
    2. yank the fire alarm conduit somewhere nobody would be able to touch both conduits at the same time
    3. shove electrical tape between the conduits where they touch
    4. who cares

    Thoughts? The only thing I've come up with after about two hours of research is NFPA 72 requirement that only intentional, permanent grounds are allowed in a fire alarm system.
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  2. #2
    Join Date
    Oct 2007
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    New Jersey
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    Quote Originally Posted by govdude View Post
    Inspecting work on a large medical campus and ran into this situation, seems wrong to me, but can't really prove or disprove that notion. Attached a sketch for clarity. Basically, we have a 480V 800A emergency generator electrical service in EMT passing from one building through another to a third building. In between, these newly installed 480V conduits make contact with the low voltage fire alarm system EMT conduits in the middle building. I took exception, and the contractor took exception to my exception .

    Researching on topics such as intersystem bonding, etc., I don't know whether:

    1. formalize a bond between the systems
    2. yank the fire alarm conduit somewhere nobody would be able to touch both conduits at the same time
    3. shove electrical tape between the conduits where they touch
    4. who cares

    Thoughts? The only thing I've come up with after about two hours of research is NFPA 72 requirement that only intentional, permanent grounds are allowed in a fire alarm system.
    I'm going with number 4. The fire alarm system won't be making use of the conduit for grounding in any event. That conduit runs back to the FACP which in turn is grounded back to the panel. I can't see it being an issue.

  3. #3
    Join Date
    Feb 2003
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    Bremerton, Washington
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    7,590
    Art 100 has a definition of intersystem bond, and your example is not an intersystem bond.

    I am not really sure there is an issue. How is this different than EMT on a unistrut rack?
    Moderator-Washington State
    Ancora Imparo

  4. #4
    Join Date
    Aug 2004
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    Northern illinois
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    15,508
    I just don't see a problem. You really don't have a ground so much as a bond and that happens thousands of times in most plants due to conduit being placed on the same piece of strut or attached to the building steel in different places.
    Bob

  5. #5
    Join Date
    Dec 2012
    Location
    Placerville, CA, USA
    Posts
    17,964
    It should only be an issue if the fire system specifications call for an isolated ground AND, contrary to normal practice for isolated grounds, the raceway is being used as the only EGC.

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