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As everyone who's ever done some plumbing knows, every fitting goes together clockwise. The more pipe you run, or the more complicated your geometry is, the more likely it is you'll end up with something you have to connect where you can't turn the ends the right way, or at all. There's a solution, of course: a union.

So the question is, what if you have that problem when you're running rigid conduit? I've never seen a union, and AFAIK using a union (or any ordinary plumbing fitting other than perhaps a coupling) is not kosher for conduit work.

But I've looked at complicated, professionally-installed rigid conduit runs where I can't imagine how they got it together conventionally. (It would be nice if I had some pictures, but I don't.) So how do they do it? Sometimes I can imagine that a left-hand thread would let you make something up tight, but I'm reasonably sure there's no such thing. But is there some kind of special conduit fitting that helps you assemble things where you can't turn them conventionally?

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What you're after, traditionally, is a three-piece coupling

The fitting you're after to join a pair of rigid conduits where you can't turn one or both conduits is called a three-piece conduit coupling. As its name implies, it consists of three pieces: a doubly-threaded (inside and outside) chase nipple, a female threaded ferrule, and a female threaded hex coupling. The chase nipple threads on one end, then the hex coupling is slipped over the other before the ferrule is threaded on. Finally, the hex coupling is pulled over the ferrule and joins to the outside threads of the chase nipple, completing the joint as depicted in this video by electrical-fittings manufacturer/distributor Garvin Industries, who I have utterly no affiliation with.

There are other options, though

However, three-piece couplings aren't the only game in town. There are set-screw and compression-type couplings available for rigid conduit (in addition to the EMT versions that folks usually know about). Furthermore, there are also split couplings that are placed over the threaded ends you wish to join together and then bolted closed much like a pipe clamp.

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    Ooohh, that "three-piece coupling" is very cute. I love the way the slender inner threaded ferrule basically turns one pipe end into one half of a union. Thank you. I suspected something like this must exist, but I didn't know what it was called and I didn't know what it looked like. And that's good info about the compression and set-screw couplings, too. Feb 20 at 21:04
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Look for “couplings” of the conduit type you’re using, e.g. “EMT couplings”. They come in a variety of types including compression and set screw (no twisting of the conduit required for the latter).

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  • Thanks! I suspected those might exist, but I'm glad to have it confirmed. Feb 20 at 21:04

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