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  • Straight Thread Vs. Tapered Thread

    Ok, for years I have heard two different stories from different electricians and co-workers. Which one is right for electrical conduit? And, where can I look it up?
    Check us out at:
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  • #2
    Re: Straight Thread Vs. Tapered Thread

    I'm not sure if this is the info you are looking for but

    a straight thread is the thread you would find on a bolt and nut.
    a tapered thread is the thread you would find on water/gas pipe connections.

    a tapered thread is a sealing thread.
    a straight thread is an axial load bearing thread.
    a straight thread does NOT seal by itself but needs a gasket or needs to be part of a tapered surface to seal. an AN/SAE fitting has a straight thread and the sealing surfaces are mating cones.

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    • #3
      Re: Straight Thread Vs. Tapered Thread

      This is an area of much confusion among many. For the record, there is NO difference between conduit threads and regular pipe threads. They are BOTH tapered. The difference in in the couplings, which are made with straight threads, so that when assembled, there are no threads showing outside of coupling for support strength. You could use regular pipe dies for electrical conduit (ridgid or IMC) threads. I do it everyday. When you purchase couplings however, plumbing couplings have tapered threads started from each end and electrical couplings have straight through threads. Conduit bodies can have mild tapered threads also, to allow the tightening of the body to the pipe.

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      • #4
        Re: Straight Thread Vs. Tapered Thread

        Newbie here; but this may help, it is from the 08 NEC

        For RMC; 344.28 of the NEC states "a 1 in 16 tapered thread"...also 344.42 which addresses RMC couplings states "Running threads shall not be used..."

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        • #5
          Re: Straight Thread Vs. Tapered Thread

          There we go! Thats the answer I am looking for I found that too in the NEC. Thank you.

          You would be suprised how many electricians would swear that that isn't so.
          Check us out at:
          http://www.fwbrental.com
          Specializing in electrical and mechanical contracting equipment!

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