Space between two RMC conduits at couplings

[Carultch]

I'm in a situation where fractions of an inch matter.

I'm working with 3-1/2" conduit, and trying to figure out how long an assembly of factory nipples and elbows really is, so that I know whether I can use factory nipples alone, or whether I need to get an extra long nipple and field-thread it.

So suppose I couple two 12" length nipples at this trade size. How long will the nipple assembly be from end to end? I'd like to know an answer that accounts for the reality dimension of the coupled ends, so please don't just say it is 24 inches without explaining.

 

[jumper]

It will vary according to the threading on the nipples and inside the coupling.

It will be longer than 24" as neither nipple will seat/screw into the coupling exactly 1/2 way.

If length is crucial, make your own out of one piece.

 

[ADub]

I think it's kind of a bogus question no offense. You'd be better off to buy 4 nipples and see what you get.


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[Carultch]

I think it's kind of a bogus question no offense. You'd be better off to buy 4 nipples and see what you get.


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I'm aware of that. I guess I just expected that there might be a standard of how much a threaded end is supposed to penetrate a coupling, at any given trade size.

 

[petersonra]

I'm aware of that. I guess I just expected that there might be a standard of how much a threaded end is supposed to penetrate a coupling, at any given trade size.

The problem is that die wear causes the threads to be different for every nipple so there is no good way to know what the length of such an assembly will be.

 

[don_resqcapt19]

I'm aware of that. I guess I just expected that there might be a standard of how much a threaded end is supposed to penetrate a coupling, at any given trade size.

There probably is, but the threads on conduit couplings and many conduit bodies are so poor that you almost have to cut and try each one.

 

[kwired]

Couplings often take threads until they hit the end of the threads or at least real close to that point - because the coupling isn't tapered. It is other fittings with tapered threads that are less predictable.

 

[Smart $]

Couplings often take threads until they hit the end of the threads or at least real close to that point - because the coupling isn't tapered. It is other fittings with tapered threads that are less predictable.

I've had a few bosses say the male threads must fully engage the coupling. Never seen any written requirement, job spec' or otherwise.

If both male and female threads were NPT, the NPT standard specifies engagement. Being the male thread is NPT, and the coupling is straight thread (NPSM), there is no specified engagement.

The closest to actually having proper engagement is when all enclosures have hubs and when using C-fittings as couplings. This way you would have all NPT threads.