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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?


Yes.

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?


Quote:
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.

Quote:
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.
Quote:
Q: What type of threads are cut on RMC and IMC?
A:
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.

http://www.steelconduit.org/Q_A.htm#13

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

Figure 5-52
Quote:
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.
http://www.tpub.com/content/construc.../14026_164.htm

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...
Quote:
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.
http://www.steelconduit.org/types.htm
I see NO mention of a coupling having a "running thread"


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

Quote:
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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