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Running Threads?

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Old 12-07-2007, 08:49 AM   #1
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Running Threads?

Are "running threads" as used in 344.42 (B) untapered threads?
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Old 12-07-2007, 10:26 AM   #2
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Re: Running Threads?


It is interesting to note that the use of "running threads" is common in electrical threaded couplings; whereas plumbing couplings of the same size have tapered threads.

The use of running threads on the conduit itself is prohibited.


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Old 12-07-2007, 12:15 PM   #3
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Re: Running Threads?

Originally Posted by kbsparky View Post

It is interesting to note that the use of "running threads" is common in electrical threaded couplings; whereas plumbing couplings of the same size have tapered threads.

344.28 Reaming and Threading.
All cut ends shall be reamed or otherwise finished to remove rough edges. Where conduit is threaded in the field, a standard cutting die with a 1 in 16 taper (3/4-in. taper per foot) shall be used.
Q: What type of threads are cut on RMC and IMC?
The NEC requires that the threads of both RMC and IMC be cut with a 3/4 inch taper per foot (1 in 16) per ANSI/ASME B.1.20.1 Standards for Pipe Threads, General Purpose (Inch). This applies to both factory and field threads. This is the same taper as standard plumbing pipe.

A"running thread" is a completely different animal than a "standard thread" and is NOT allowed to make up couplings:

Figure 5-52
All types of conduit must be reamed after they have been cut. Conduit threaded in the field must be threaded with a die that has a 3/4-inch taper per foot. When threaded conduit enters a box or fitting, a bushing must be used to protect the conductor insulation from being cut or tom. Also, for those types that use threaded couplings, running threads, as shown in figure 5-52, are not to be used for connection at couplings. Running threads weaken the conduit and may come loose.

If you are finding "running threads" in conduit as the norm....something is seriously wrong in your part of these United States.

The couplings are also tapered...
Rigid metal conduit (RMC) is a listed threaded metal raceway of circular cross section with a coupling which can be either a standard straight tapped conduit coupling or the integral type.
I see NO mention of a coupling having a "running thread"

Originally Posted by kbsparky View Post
The use of running threads on the conduit itself is prohibited.
Not exactly....

344.42(B) Running Threads
Running threads shall not be used on conduit for connection at couplings
You CAN use a running thread to enter a box with or w/o a myers hub.
The code applies to COUPLINGS - not the conduit.

If I had 2 panels, mounted 4 3/8" apart, I could use a "running thread" on my RMC to connect them to each other - with no violation of NEC articles.

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