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Thread: GROUND SCREWS IN METAL JUNCTION BOXES

  1. #1
    Join Date
    May 2004
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    GROUND SCREWS IN METAL JUNCTION BOXES

    Hi guys. I am an apprentice with a question that I have received varying answers. Do metal junction boxes require a grounding screw with pigtail? Several Journeymen have stated that if you run metal conduit, the conduit is considered grounded, thus a ground screw in every j-box is not required (the same answer applies if you're running MC cable). However, 1 guy (the one who I first started with says they are required). I spent 20 years in the US Navy onboard Nuclear Submarines. The manuals for operating a nuclear power plant are not as confusing as the NEC 2002. I do not know if a definitive answer is a viable option but anything would help, especially a code reference. Thanks guys.
    Gary Thomas
    Greenville, SC

  2. #2
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    Re: GROUND SCREWS IN METAL JUNCTION BOXES

    See 250.148(A)


    (A) Metal Boxes. A connection shall be made between the one or more equipment grounding conductors and a metal box by means of a grounding screw that shall be used for no other purpose or a listed grounding device.
    Edited to include reference.

    [ May 09, 2004, 12:16 PM: Message edited by: ryan_618 ]
    Ryan Jackson, Salt Lake City
    Inspector, Instructor

  3. #3
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    May 2004
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    Re: GROUND SCREWS IN METAL JUNCTION BOXES

    Thanks. I read that also. o you have any idea where these other guys came up with thier idea that the conduit fulfills the requirement of the ground?
    Gary Thomas
    Greenville, SC

  4. #4
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    Re: GROUND SCREWS IN METAL JUNCTION BOXES

    It is not as clear as yes or no.

    If you have metal raceway with metal boxes and you do not have spliced or terminated conductors within the box you do not have to install the grounding pigtail.

    So a true pull box is not required to have a grounding pigtail. Make it a junction or device box and the box must be connected to the grounding conductor.

  5. #5
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    Re: GROUND SCREWS IN METAL JUNCTION BOXES

    Section 250.118 lists the allowed equipment grounding (bonding) conductors, which allows metal raceway, AC cable, MC cable..... A seperate green wire is not required by the NEC in a metal raceway, but it may be a good idea.
    Moderator-Washington State
    Ancora Imparo

  6. #6
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    Re: GROUND SCREWS IN METAL JUNCTION BOXES

    Conduit is a listed grounding conductor.

    You can choose not to run a separate copper grounding conductor

    Then you would need a jumper from the box to receptacles also.

  7. #7
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    Re: GROUND SCREWS IN METAL JUNCTION BOXES

    Garosan: you understand nuclear power plants because the navy sent you to school for your rate, nuclear power school, prototype and then to the fleet. If you just jumped into the NEC you have problems with it. I recommend a book by the NFPA "Users Guide to the NEC", and then Vol 1 and 2 of Mike Holts Understanding the NEC
    I was in the navy as a mechnical operator and made the tranistion to a electrican with no problems.
    Tom Baker, Class 70-4.
    Moderator-Washington State
    Ancora Imparo

  8. #8
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    Re: GROUND SCREWS IN METAL JUNCTION BOXES

    With metal boxes and metal conduit, 250.146 (A) (B) and (C) allows some devices to be installed with out a wire grounding jumper.
    In my area, we mostly use metal conduit and grounding is done a great deal of the time with listed self grounding devices, and no jumper.
    Russ Burbank IL

  9. #9
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    Re: GROUND SCREWS IN METAL JUNCTION BOXES

    Still you will need to ground the box.

  10. #10
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    Burbank IL
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    Re: GROUND SCREWS IN METAL JUNCTION BOXES

    Bob, I'm not sure what you mean. 358.2 says EMT can be use as an equipment grounding conductor when installed utilizing appropriate fittings.
    The box would already be grounded.
    Russ Burbank IL

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