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Thread: Bonding bushings

  1. #1

    Default Bonding bushings

    I just had my inspection today for my 400A service. Passed good enough to get the stickers applied to the meter base and panel, but the inspector commented that my bonding bushings should have a locknut under them. I do have a locknut on the outside of the box, just not on the inside sandwiched between the box and the bushing. I've tried to do this in the past, but rarely are the conduit threads long enough to get that bonding bushing on far enough for my satisfaction (so the set screw fully hits threads).

    So are service bonding bushings (the metal ones with a lug, set screw, and non metallic ring to protect the wires) considered inadequate to hold conduits in place? How many threads are required to engage the conduit?

    I don't think the inspector is going to make me change that, it seemed more like a comment. He seemed to buy my reasoning of not enough thread. What do you guys think?

  2. #2
    Join Date
    Sep 2002


    You are not alone in this problem. Many connectors and often the conduit threads themselves just don't have enough for both bushing and locknut. Frustrating isn't it. If it is tight enough that the conduit is secured to the cabinet, I wouldn't worry about it, especially since everything that should be, is properly bonded.

  3. #3

    Default Good post

    We are all having that proplem, but you must have atleast three threats exposed, so you can screw your bushing on. I usually tap my nut on with my screw driver, until I can get three threats or more.
    Learning brings success

  4. #4


    I can find where the conduit must be firmly secured where entering a box. I can not find anywhere it forbids metal bushings to be used to secure to a box. As far as I can find the NEC is mute on that subject other than 110.3.B calling for installation instructions to be followed. Check installation instructions, you may find your metal bushings to be listed as a securing device to boxes.

    However there is a rule in 300.4 that forbids plastic bushings from being used to secure to a box.


    Conduit bushings constructed wholly of insulating material shall not be used to secure a fitting or raceway. The insulating fitting or insulating material shall have a temperature rating not less than the insulation temperature rating of the installed conductors.

    I find no rule against use of a bushing for securing to box. Check installation instructions to see if your bushing is listed for use as a securing device. May be there.

    Trying to help


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