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Thread: Grounding locknuts vs. Ground bushings

  1. #1
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    Grounding locknuts vs. Ground bushings

    When bonding, where can and can't you use grounding locknuts. Where do you have to use ground bushings. And do you need either one when nippling through panels, gutters connected to panels and xfmrs ect. ? I have always used ground bushings for my installations but the locknut is the new, cheap, and UL LISTED thing so I want to make sure I use it correctly. I also can't seem to find anything in the code to tell me this info. What section can I refer to for an inspector if he questions my installation?

    [ August 13, 2005, 10:50 PM: Message edited by: FRERUCHA ]

  2. #2
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    Re: Grounding locknuts vs. Ground bushings

    Grounding bushings, grounding locknuts or grounding wedges are required on a service on the line side of the service disconnect. Grounding bushings are also required for the bonding of metal boxes etc. where the voltage exceeds 250 volts and concentric or eccentric KO's are encountered. That is unless the box with the KO's are listed specifically for bonding over 250 volts than they are not required. Gutters, panels or xfmr's wouldn't require them if the KO's where the same size as the nipple or conduit entering it.

    [ August 13, 2005, 10:52 PM: Message edited by: infinity ]
    Rob

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    All responses based on the 2011 NEC unless otherwise noted

  3. #3
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    Re: Grounding locknuts vs. Ground bushings

    I understand on the load side of the service if more than 250v to ground, but I've been told you can use the grounding lock nut , with exception of ko's, every where you used to be required to use ground bushings. Is this true and is there literature on this somewhere?

  4. #4
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    Re: Grounding locknuts vs. Ground bushings

    I understand on the load side of the service if more than 250v to ground
    On the line side, grounding bushings, locknuts or wedges are required regardless of the voltage.

    I would agree with the second half of your post that grounding locknuts would be a suitable substitute for grounding bushings where those specific KO's I mentioned aren't encountered.

    [ August 13, 2005, 11:09 PM: Message edited by: infinity ]
    Rob

    Chief Moderator

    All responses based on the 2011 NEC unless otherwise noted

  5. #5
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    Re: Grounding locknuts vs. Ground bushings

    for your code references ('95) try 250.92(B) and 250.97
    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.

  6. #6
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    Re: Grounding locknuts vs. Ground bushings

    As far as I know bonding bushings and bonding locknuts are interchangeable for bonding.

    The downside with bonding locknuts is that many times you are dealing with conductors 4 AWG and larger so some type of bushing is required.

  7. #7
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    Re: Grounding locknuts vs. Ground bushings

    interchangeable
    IMHO, I think not. In this area the gr. locknuts only have a "binding screw", no lug. If you are bonding to meet code requiremnts and there are no concentric/eccentric knockouts the locknut works fine. If you do have such knockouts the "binding screw" on the locknut bites into a concentric ring, not into the enclosure itself, and a bushing with attached bonding conductor is required.
    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.

  8. #8
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    Re: Grounding locknuts vs. Ground bushings

    Originally posted by augie47:
    IMHO, I think not.
    It's good you don't take my word for it, no one should.

    At this point the place to go is the UL White Book.


    GROUNDING AND BONDING EQUIPMENT (KDER)

    USE


    This category covers bonding devices, ground clamps, grounding and bonding bushings and locknuts, ground rods, armored grounding wire, protector grounding wire, grounding wedges, ground clips for securing the ground wire to an outlet box, water meter shunts, and similar equipment.
    Grounding and Bonding Bushings — Bonding bushings for use with conduit fittings, tubing (EMT) fittings, threaded rigid metal and intermediate metal conduit, or unthreaded rigid metal and intermediate metal conduit are provided with means (usually one or more set screws) for reliably bonding the bushing (and the conduit on which it is attached) to the metal equipment enclosure or box. They provide the electrical continuity required by the NEC at service equipment and for circuits rated over 250 V. Means for connecting a grounding or bonding wire are not provided and if there is need for such a conductor a grounding bushing should be used.

    Grounding bushings for use with conduit fittings, tubing (EMT) fittings, threaded rigid metal and intermediate metal conduit, or unthreaded rigid metal and intermediate metal conduit have provision for the connection of a bonding or grounding wire or have means for mounting a wire connector available from the manufacturer. Such a bushing may also have means usually one or more set screws) for reliably bonding the bushing to the metal equipment enclosure or box in the same manner that this is accomplished by a bonding bushing. Grounding bushings provide the electrical continuity required by the NEC at service equipment and for circuits rated over 250 V. They may be used with or without a bonding or grounding conductor as determined by the bonding or grounding function that is intended to be accomplished.

    Insulating throat liners in grounding or bonding bushings are suitable for temperatures of 150°C if they are black or brown in color. Unless otherwise marked, insulating throat liners of any other color are suitable for temperatures of 90°C.
    After all that is this.

    Grounding and Bonding Locknuts — Grounding and bonding locknuts serve in a manner similar to grounding and bonding bushings except they do not provide abrasion protection for the conductor at the end of the conduit.
    IMO, UL says I can use a bonding locknut anyplace I need a bonding bushing but do not need abrasion protection.

  9. #9
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    Re: Grounding locknuts vs. Ground bushings

    had alredy been there to try and prove my point,..,,,,couldn't
    but...i still contend, if the ground path from the locknut depends on those lil tabs of the eccentric knockouts, we haven't accomplished what we want.,.especially with service fault currents....
    been there seen that...

    i'll keep searching....lol
    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.

  10. #10
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    Re: Grounding locknuts vs. Ground bushings

    augie, keep in mind UL also lists reducing washers as suitable for grounding purposes.

    Run a 1/2 EMT containing a 480 volt circuit into a 1" KO using reducing washers and UL considers it grounded.

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