Are conduit or pipe threads used in Class 1, Div 1 Enviroments? 2

[chinalake]

I am not clear on which type of dies to use threading 1/2" conduit for a Class 1, Div 1 installation. My understanding is that conduit threads are "straight threads" for mechanical construction, and that pipe threads are tapered for sealing. The NEC 346-8 refers to ANSI B.1.20.1. Is there something I missed in the NEC or ANSI B.1.20.1 that states which treads should be used?

 

[resqcapt19]

All conduit threads are required to be tapered threads. Conduit couplings use straight threads, but the conduit itself uses the same threads as plumbing pipe. 344.28 (348-8 in the '99 code)in the NEC requires all field cut conduit threads to have a 3/4" to the foot taper.

Don

 

[busbar]

Other supporting verbiage:

99NEC500-3. General.
(d) Threaded Conduit. All threaded conduit referred to herein shall be threaded with an NPT standard conduit cutting die that provides 3⁄4-in. taper per foot. Such conduit shall be made wrenchtight to prevent sparking when fault current flows through the conduit system, and ensure the explosionproof or dust-ignitionproof integrity of the conduit system where applicable.

 

[abeltio]

A field note...
If you are preparing a spec for conduit, please do add that an anti-seize compound be applied to all threads prior to final assembly.
cheers.
a.

 

[resqcapt19]

Good point, Abeltio. The 2002 code requires an approved conductive corrosion protective coating for all field cut threads in area where the conduit requires corrosion protection. See 300.6(A).
Don

 

[jron]

You said that "344.28 (348-8 in the '99 code)in the NEC requires all field cut conduit threads to have a 3/4" to the foot taper." Does this also apply to factory threaded conduit?

 

[busbar]

http://www.alliedtube.com/grc.pdf

Column 1 calls out the ¾-inch-per-foot taper and ANSI B.1.20.1. It’s very likely that listed galvanized-steel and aluminum conduit and IMC have the same characteristics. The details would probably be described in the corresponding UL standard.