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

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

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

(OP)
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?

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

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

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

2
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.
  

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

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.

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

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

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

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?

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


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.
  

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