Designer69
Senior Member
I see 1/2" or 1-1/2"NPT on drawings all the time. still don't know what it stands for. anyone know?
thanks
thanks
what is NPT?
- Thread starter Designer69
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Rick Christopherson
Senior Member
NPT = National Pipe Thread
- Location
- Massachusetts
National Pipe Thread Tapered
- Location
- Massachusetts
glene77is
Senior Member
- Location
- Memphis, TN
- Location
- New Jersey
- Occupation
- Journeyman Electrician
Tapered threads are required by the NEC for RMC. I still occasionally see some NPSM or American Standard Straight Mechanical Pipe Thread dies on the job. Guys tell me that it allow the locknuts to go on easier. :roll:
- Location
- Illinois
- Occupation
- retired electrician
While, as Rob pointed out, conduit threads are required to be taper threads, conduit couplings are straight threads.
Rob, I read that section as requiring field-threaded conduits to have tapered threads..so does that mean that factory-made threads can be non-tapered?
I have never really paid attention to the type of threads on factory-threaded RMC. Maybe someone here can take a look at their inventory.
- Location
- Massachusetts
Conduit comes with tapered threads.
LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
All the factory threads I've ever seen (or noticed) were tapered, just like we make 'em.
can someone clarify?
can someone clarify?
there are 2 types of threads ,the tapered threads and the non-tapered or parallel threads ,taperd thresds are what I have always met in the field and in equipment assembly.Non tapered threads usually provide a more water tight seal,but,are there any specific places or applications where the parallel thread is to be used?
can someone clarify?
there are 2 types of threads ,the tapered threads and the non-tapered or parallel threads ,taperd thresds are what I have always met in the field and in equipment assembly.Non tapered threads usually provide a more water tight seal,but,are there any specific places or applications where the parallel thread is to be used?
- Location
- Illinois
- Occupation
- retired electrician
If non-tapered threads provide a more watertight seal, why does plumbing pipe use the same taper as we do? The only difference being that their couplings also use tapered threads.
Really? I thought rigid conduit and most fittings are straight threads? Isn't spinning on a lock nut the way to tell -- if it easily spins all along the thread, it is straight. If it gets tighter the further on the nut goes, eventually needing a wrench to turn it, then the threads are tapered?
I've had issues when buying conduit cut to length and then threaded with NPT threads -- the locknut that goes deepest may not easily go on as far as I would like. Or did the guy threading it just not thread enough of the pipe?
I've had issues when buying conduit cut to length and then threaded with NPT threads -- the locknut that goes deepest may not easily go on as far as I would like. Or did the guy threading it just not thread enough of the pipe?
mtfallsmikey
Senior Member
depends on the condition of the dies, and how far they are run up the pipe.....don't mind me, I'm just the house plumber
Our rigid couplings are what the plumbers call "thread protectors". They are a little longer than a [plumbing] pipe coupling.
LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
I believe that's so the threads will engage fully before the pipes butt.
NPT - National Pipe taper
NPS - National pipe straight
Tapered threads have a slight taper towards the end of the fitting. When the threads are mated and screwed together, they compress to form a seal. Pipe tape or joint compond is used more as a lubricant then for sealing. Rigid conduit has tapered threads. Lock nuts will work on NPT threads and will provide a mechanical connection but not a seal that might be needed to for a classified enviroment or to maintain the integirty of an enclosures rating. You would need a hub for that.
Straight (parallel) threads maintain the same diameter along their entire length. They're used for mechanical joining and serve one purpose?to hold a fitting in place. Straight threads require a seal to make a water tight connection. One use of straight threads is on explosion proof pilot operators. They thread into the cover of explosion proof enclosures (about a 1/2" thick) using 3/4" NPS threads.
NPS - National pipe straight
Tapered threads have a slight taper towards the end of the fitting. When the threads are mated and screwed together, they compress to form a seal. Pipe tape or joint compond is used more as a lubricant then for sealing. Rigid conduit has tapered threads. Lock nuts will work on NPT threads and will provide a mechanical connection but not a seal that might be needed to for a classified enviroment or to maintain the integirty of an enclosures rating. You would need a hub for that.
Straight (parallel) threads maintain the same diameter along their entire length. They're used for mechanical joining and serve one purpose?to hold a fitting in place. Straight threads require a seal to make a water tight connection. One use of straight threads is on explosion proof pilot operators. They thread into the cover of explosion proof enclosures (about a 1/2" thick) using 3/4" NPS threads.
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