Electrical Pipe Threads?

Discussion in 'Shop Talk' started by Big Dave, Jun 18, 2006.

  1. Big Dave

    Big Dave Well-Known Member

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    I need some clarification. If there is anyone out there that could help I would be much oblige to ya. I am trying to find on the internet the differance between plumbing pipe threads and electrical pipe threads. I belive the plumbers threads are tapered, but what are straight threads? I went to work for an electrical company an I am trying to ge this figured out. Thanks for any help
     
  2. Dahc

    Dahc Don't Tase me, bro!?!

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    Their is no difference in the threading on rigid conduit (electrical) and the threading on cast iron water pipe. Same thing cut by the same type of machine. Threads are a "V" type thread and looks kinda like this ^^^^^ from the side. I have worked in both trades but am not an expert on either one. I did an aweful lot of bending and threading though.

    Once opon a time when I worked, I did industrial electrical rough in. I liked it. Good money without your normal "good money people" working with you if you catch my drift. Anyone who asks you to go the bucket of air, the wire stretcher or the sky hook can't be trusted. You'll need that info in the trade. lol.
     

  3. Big Dave

    Big Dave Well-Known Member

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    Thanks for your reply. I guess you were the only one that had any knowledge on this subject to share. I can relate how you describe things.
     
  4. tiogacounty

    tiogacounty Well-Known Member

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    Threads are awfully similar, although I have only threaded a couple of thousand pieces of IMC and ridgid, never black iron or galv. One interesting thing is that galv. plumbing pipe cannot be replaced by ridgid electrical conduit. It works fine, but conduit is made from some pretty questionable steel, and apparently not well galvanized on the interior. I worked with a guy who cut a nipple from conduit and patched a pipe at home. It didn't last a year until it rotted out.
     
  5. agmantoo

    agmantoo agmantoo Supporter

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    Plumbing threads and eletrical threads are the same threads per inch. However, plumbing threads are tapered for sealing and electrical threads are straight permitting a nut to travel the entire length of the thread.
     
  6. rambler

    rambler Well-Known Member Supporter

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    That's what I was thinking, there is a difference. Water pipe gets tight from the taper of the threads; electrical gets tight from bottoming out on a flat collar or lack of threads.....

    --->Paul
     
  7. farminghandyman

    farminghandyman Well-Known Member Supporter

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    some info I found,

    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.

    http://www.steelconduit.org/pdf/ConGuideGeneral.pdf

    http://www.wheatland.com/cdrom/ConGuide.pdf

    "4.1.1 Cutting and threading RMC and IMC
    (NOTE: Although coupling threads are straighttapped,
    conduit threads are tapered.)"


    http://www.steelconduit.org/pdf/ConGuide4.3.pdf
     
  8. Dahc

    Dahc Don't Tase me, bro!?!

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    Guess I didn't know as much as I thought I did, huh Big Dave? Don't worry, your employer will supply the proper blades for cutting the threads. I hate being wrong.
     
  9. rambler

    rambler Well-Known Member Supporter

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    Um - you were right tho, we were wrong? It's tapered pipe thread, sure enough.

    --->Paul
     
  10. agmantoo

    agmantoo agmantoo Supporter

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    I read the article and I gleaned that both types of threads are used. I cannot get the segment, on both types of threads, of the article to copy and paste as I need file conversion software which I do not have. In this article http://www.wheatland.com/cdrom/ConGuide.pdf
    read 4.3.4 I guess all of us were partially correct :)
     
  11. tiogacounty

    tiogacounty Well-Known Member

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    Electrical threads are tapered also. The exception is if you buy, or make, "running thread" which is just an all threaded nipple. If you overtighten a piece of ridgid conduit into a standard coupling you will notice that the coupling actually flares a bit as the taper expands the opening.