I got this grounding bushing for the pipe in the service mast. I am screwing it to a compression fitting that is in the back of the panel. What’s goofy is there is a rubber washer, black anyway, in the grounding bushing??? The bushing is weird too. It’s got two screws each on a different radius. One sits up higher…
I am going to run #6 from the bushing to the ground bus.
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The 'washer' is intended to reduce the chances of the conductors having their insulation damaged when they are pulled in.
One of those screws is designed to lock the bushing in place and prevent it from spinning and loosening. The other, usually slightly longer, will accept a 'crows foot', an open lug, or other lug to accept the bonding conductor.
A few grounding bushings have an integral lug and two screws to lock the bushing in place.
Just for general information there are also grounding wedges. These are used under a locknut. These wedges look like horseshoes. These are very handy. You get all the conductors landed and find you left out the grounding bushing. No need to disconnect them. You just loosen the existing locknut and slide it up the conductors coming out of the conduit a bit.
Then between the locknut and connector you insert the wedge. The opening in the horseshoe shape allows you to slip the conductors into the center. Slide the wedge down around the connector sticking up and replace the locknut driving it tight. Saves a lot of time.
Another device under a dollar that you don't need often but when you do it gets you out of a fix. When I run a full service truck I try to keep a small selection of these on hand.
I'll take a shot at this, even though I'm having a little trouble visuall-izing it. Sounds like you have a blackjack style bushing. The grounding bushing is used to bond the nipple containing unfused conductors to the ground, usually when you have used a concentric knockout. Normally you would use a grounding locknut with a plastic bushing if you didn't have concentrics. Is this on the service mast or is it on a nipple from the meter to your loadcenter/panelboard...is this compression fitting on emt, because some locals do not allow this. I see the new 2005 code does not allow rt emt connectors over 2inch, unless they have an o-ring, some inspector is knocking over new 400 amp services already even though this isn't adopted yet, they just can't wait.
Thanks guys I think I got it. I took the bushing out of the bag and it's now easy to see the plastic thing is a slip ring to protect the conductors.
I am the inspector, the local, and the chief bottle washer so nobody is going to complain too much.
My compression fitting is going on 2" rigid. I am not going to buy a nipple or have my piece threaded. The two inch rigid was too much money, $50. Mast height won't allow all ten feet and only one end now has thread. I can't see that compression vs. nipple will make a difference.