jmellc
Senior Member
- Location
- Durham, NC
- Occupation
- Facility Maintenance Tech. Licensed Electrician
How is taper measured?
Rigid Threads
- Thread starter jmellc
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With a thread gauge.
While I was an apprentice I tried to tell an old timer that nobody outside of the electricians should use our stock & dies but would not listen and threaded at least ten pieces of pipe for a 120# steam line. He spent awhile taking apart a leaking joint to have another & another leaking joint. Mean while read that chase nipples have straight thread. I know quality steel ( not garbage die cast ) chase nipples a steel locknut will easily spin to the very end. Might be the reason inspectors tell you that straight thread chase nipples should not be screwed into heavy wall couplings. On extra small pecker head on small IEC motors that had posts to connect wires we always used a chase nipple threaded to a coupling on outside of pecker head to save space.
4-20mA
an analog man in a digital world
- Location
- Charleston SC
- Occupation
- Process Control, Instrumentation & Electrical
I believe they all use the same taper. "We" adopted threaded pipe from "them."
All threaders cut straight threads if you run them up the pipe far enough.
Rings a bell...
4-20mA
an analog man in a digital world
- Location
- Charleston SC
- Occupation
- Process Control, Instrumentation & Electrical
Per foot? or per inch?
LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
4-20mA
an analog man in a digital world
- Location
- Charleston SC
- Occupation
- Process Control, Instrumentation & Electrical
Yes, duh... read it wrong! I'll sit down now and finish my lunch.
4-20mA
an analog man in a digital world
- Location
- Charleston SC
- Occupation
- Process Control, Instrumentation & Electrical
I was thinking it read as the taper needed to be 3/4" long... like typical threads... I'm still confused I think
- Location
- New Jersey
- Occupation
- Journeyman Electrician
The taper for a 3/4"long thread would be 1/16 of an inch.I was thinking it read as the taper needed to be 3/4" long... like typical threads... I'm still confused I think
4-20mA
an analog man in a digital world
- Location
- Charleston SC
- Occupation
- Process Control, Instrumentation & Electrical
That's what I was referring to in my feeble attempt.
wwhitney
Senior Member
- Location
- Berkeley, CA
- Occupation
- Retired
3/4" per foot is (3/4")/12" = 1/16.
So the taper for a 1" long thread would be 1/16". For a 3/4" long thread it would be 3/64".
Cheers, Wayne
- Location
- New Jersey
- Occupation
- Journeyman Electrician
Correct, that's what happens when you do stuff in your head.
Eddie702
Licensed Electrician
- Location
- Western Massachusetts
- Occupation
- Electrician
Ridgid designates their dies as "NPSM"=National pipe straight mechanical or "NPT"=National Pipe Taper
I was always told electrical dies cut straight and pipe dies were tapered. But as others posted above apparently that is not true according to 344.28. I always used pipe dies anyhow because that is what I had.
I was always told electrical dies cut straight and pipe dies were tapered. But as others posted above apparently that is not true according to 344.28. I always used pipe dies anyhow because that is what I had.
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LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
I can't imagine starting or running a non-tapered die.
- Location
- New Jersey
- Occupation
- Journeyman Electrician
When I started in the business in the 80's we used the straight dies. We were taught on the job and in apprentice school that we used "electrician" dies. To this day some people still think that "plumber" dies are not for electrical conduit.
Fred B
Senior Member
- Location
- Upstate, NY
- Occupation
- Electrician
Right. Not sure but would you first run a NPT die first the run a straight thread on up to a shouldered edge? The pitch is the same for both NPT and NPS.I can't imagine starting or running a non-tapered die.
synchro
Senior Member
- Location
- Chicago, IL
- Occupation
- EE
I can't imagine starting or running a non-tapered die.
The dies for NPS threads have an initial "chamfer" region which ramps down the diameter when it is cutting the threads, after which it cuts the threads at a constant diameter. The end of the die also has a short chamfer to avoid making a shouldered edge.
If you initially ran an NPT die to its full extent, then the first half or so of the threads would have a smaller diameter than would NPS threads. You can make straight threads by running an NPT die further down the conduit, but they would have a reduced diameter compared to NPS threads.
Fred B
Senior Member
- Location
- Upstate, NY
- Occupation
- Electrician
Good to know.
So the Rigid I've gotten usually come with one end a threaded coupling installed but not necessarily tightened, but it is usually at full length of rigid threads. It is definitely different than the plumbing coupling. Is the rigid coupling a nps or npt cut?
- Location
- New Jersey
- Occupation
- Journeyman Electrician
Electrical couplings have straight threads.
Just wondering if it would be safer if taper threads were on heavy wall couplings in explosion proof areas. A lot of sparkies do not know that you are not suppose to thread in a straight thread chase nipple into a heavy wall coupling. Have done it and always tightened them up and never came loose.
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