RMC conduit going into box w/concentric KO's

Sure it is, and just spin on a 1/2" threaded grounding bushing and you'll be well grounded

I agree. The reducing bushing will look kind of hokey. Put a 1/2" bonding bushing on after the locknut and attach a grounding pigtail to it. Once the box and conduit are fastened securely the concentric KO should not work itself loose.

I think running a separate grounding conductor is the best way to go.

Yes that also would be my understanding for any 'new' work; to current codes. Existing conduit previously used as grounding 'might' be grandfathered although some jurisdictions inspections may reject it if other work is being done in same area.

Yes that also would be my understanding for any 'new' work; to current codes. Existing conduit previously used as grounding 'might' be grandfathered although some jurisdictions inspections may reject it if other work is being done in same area.

It's perfectly acceptable by current NEC

Here's a little tip that me and my brother use when dealing with loose concentric KO rings. We take a conduit punch and turn it backwards so the flat parts are on either side of the ring. When the screw is tightened, the ring is mashed back into place and is tighter than it was to start with.

TDD

Thanks all for the replies.

BTW I got my permit in 2006 at which time my county was using NEC

I will definitely be using the grounding bushing to insure box-to- conduit ground. John mentioned to use the grounding bushing after the locknut. Couldn't the grounding bushing be used by itself? The ones I've seen are pretty beefy compared to the locknuts. Is it code or personal preference that you use both?

--zeb

I've always used the locknut then a bushing. I guess you would have to find out from the manufacturer if their bushing was approved to function as a locknut would. You may find that the bushing will not screw all the way down enough to lock the pipe in place.