Pipe Thread ?

 
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Old 04-27-2009, 11:38 PM   #1
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Pipe Thread ?


What's the difference between electrician's pipe thread and plumbers pipe thread? There was some discussion on this today at work and nobody seemed to know for sure. Thanks..
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Old 04-28-2009, 12:07 AM   #2
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Re: Pipe Thread ?


Plumbers and pipefitters use NPT, National Pipe - Tapered. Dedicated electrical contractors use NPSM, National Pipe- Straight Mechanical. Tapered pipe thread, because it is tapered, seals as it is tightened. Straight thread has a much higher degree of latitude, the fittings can be screwed much further into boxes, for instance.

I worked for years at a large mechanical contractor, and we used NPT dies on all out Rigid machines, because there was too much chance of a Fitter using the Sparky's machine by mistake.

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Old 04-28-2009, 12:08 AM   #3
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Re: Pipe Thread ?


nothing, there both the same. we both use the same threading equipment to make the threads
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Old 04-28-2009, 12:15 AM   #4
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Re: Pipe Thread ?


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Originally Posted by johndel1971 View Post
nothing, there both the same. we both use the same threading equipment to make the threads
That is in error. One is straight, one is tapered. Unless the electricians are using NPT

http://www.ridgid.com/ASSETS/1EE6566..._Selection.pdf
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Old 04-28-2009, 07:16 AM   #5
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Re: Pipe Thread ?


I'll stick my 2 cents in here. Anti-wing nut you are completly right. I know this because I was an Industrial Electrician for 25 yrs. I have even heard arguments about if it was against code to use NPT for conduit or not............. I still don't know ..........
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Old 04-28-2009, 07:55 AM   #6
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Re: Pipe Thread ?


The rigid pipe electricians use is tapered.

It's required to be.

NEC 344.38 "..........Where conduit is threaded in the field, a standard cutting die with a 1 in 16 taper (¾-in. taper per foot) shall be used.
FPN: See ANSI/ASME B.1.20.1-1983, Standard for Pipe Threads, General Purpose (Inch)."
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Old 04-28-2009, 03:46 PM   #7
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Re: Pipe Thread ?


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Originally Posted by 480sparky View Post
The rigid pipe electricians use is tapered.

It's required to be.

NEC 344.38 "..........Where conduit is threaded in the field, a standard cutting die with a 1 in 16 taper (¾-in. taper per foot) shall be used.
FPN: See ANSI/ASME B.1.20.1-1983, Standard for Pipe Threads, General Purpose (Inch)."
Sparky,

You are so right. I was last involved in this stuff almost twenty yeaars ago. And our electricians used the fitters NPT dies, so we didn't have a clustered mess, but I knew then that outfits like dedicated (we were a control company with fitters and electricians) electrical contractors often preferred NPSM.
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Old 05-01-2009, 06:10 PM   #8
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Re: Pipe Thread ?


I'm glad someone brought this up. I have never known the correct answer myself. Is 1 in 16 (3/4" taper per foot) the same as NPT?
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Old 05-02-2009, 01:24 AM   #9
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Re: Pipe Thread ?


Yes, all NPT is tapered at 1/16 (3/4" per foot). That is what makes it NPT.
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Old 05-02-2009, 06:19 AM   #10
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Re: Pipe Thread ?


I'm not sure where or how this straight thread rumor ever started, but it seems to be prevalent. I've got catalogs that go way back, and electrician's threads have always been tapered. I'll admit that I know contractors who have used straight thread dies, but that's never been the correct method.
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Old 05-02-2009, 08:54 AM   #11
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Re: Pipe Thread ?


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I'm not sure where or how this straight thread rumor ever started, but it seems to be prevalent. I've got catalogs that go way back, and electrician's threads have always been tapered. I'll admit that I know contractors who have used straight thread dies, but that's never been the correct method.
It comes from the UMEC (Urban Myth Electric Code). Don't you have a copy, Marc?

You may know some of the Articles in it: 100-foot maximum pipe run, no wire nuts in a panel, receptacle height requirements for dwellings, tandem breakers are for MWBCs, no splices in condulet bodies, requirements for 3-way switches at stairwells.......
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Old 05-02-2009, 09:32 AM   #12
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Re: Pipe Thread ?


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What's the difference between electrician's pipe thread and plumbers pipe thread? There was some discussion on this today at work and nobody seemed to know for sure. Thanks..
It depends who's writing and posting those threads... If it's comedy you're lookin' for, I would say read the plumber's threads--those guys are HILLARIOUS !
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Old 05-02-2009, 10:33 AM   #13
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Re: Pipe Thread ?


So I guess the real question is can i go to the Home depot and buy nipples in the plumbing dept and use them between the meter can and the panel??
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Old 05-02-2009, 10:34 AM   #14
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Re: Pipe Thread ?


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So I guess the real question is can i go to the Home depot and buy nipples in the plumbing dept and use them between the meter can and the panel??
No, but only because they are not UL listed and no other reason.
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Old 05-03-2009, 04:26 PM   #15
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Re: Pipe Thread ?


Quote:
No, but only because they are not UL listed and no other reason.
Is the UL listing somehow marked onto the electrical nipples?
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Old 05-03-2009, 06:58 PM   #16
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Re: Pipe Thread ?


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Is the UL listing somehow marked onto the electrical nipples?
The UL only requires the 10' stick to be marked. The carton the nipples come in is marked UL-6.

Last edited by mdshunk; 05-03-2009 at 07:04 PM.
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Old 05-03-2009, 09:30 PM   #17
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Re: Pipe Thread ?


Quote:
Originally Posted by 480sparky View Post
It comes from the UMEC (Urban Myth Electric Code). Don't you have a copy, Marc?

You may know some of the Articles in it: 100-foot maximum pipe run, no wire nuts in a panel, receptacle height requirements for dwellings, tandem breakers are for MWBCs, no splices in condulet bodies, requirements for 3-way switches at stairwells.......
another myth the high leg must be marked orange
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Old 05-03-2009, 09:31 PM   #18
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Re: Pipe Thread ?


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So I guess the real question is can i go to the Home depot and buy nipples in the plumbing dept and use them between the meter can and the panel??
bonding bushings
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Old 05-03-2009, 09:41 PM   #19
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Re: Pipe Thread ?


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another myth the high leg must be marked orange
110.15?
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Old 05-03-2009, 09:43 PM   #20
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Re: Pipe Thread ?


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bonding bushings
What about them??

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