greymatter
Member
Does anyone know the minimum number of threads required (per code) for a proper conduit/coupling connection?
conduit/coupling connection
- Thread starter greymatter
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LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
Brain, welcome to the forum! 
The closest I've seen is "wrenchtight."
The closest I've seen is "wrenchtight."
greymatter
Member
conduit/coupling connection
thanks for the reply...but this is a question on the Journeyman's test and gives you a 'thread count' choice of 1, 3, 5, or 10. I assume that it's 3 (1 too short, 10 too long), but not sure...and I can't find it in the code book.
thanks for the reply...but this is a question on the Journeyman's test and gives you a 'thread count' choice of 1, 3, 5, or 10. I assume that it's 3 (1 too short, 10 too long), but not sure...and I can't find it in the code book.
jumper
Senior Member
- Location
- 3 Hr 2 Min from Winged Horses
5 full threads if we are talking about an Article 500 explosion proof install, 500.8(D) , '05 code.
greymatter
Member
conduit/coupling connection
hey jumper,
Article 500 is for explosion proof install...do you know if 5 threads is the same requirement for a (minimum) regular conduit to coupling connection?
hey jumper,
Article 500 is for explosion proof install...do you know if 5 threads is the same requirement for a (minimum) regular conduit to coupling connection?
LJSMITH1
Senior Member
- Location
- Stratford, CT
This is from the Steel Tube Institute of North America - "Guide for Installing Steel Conduit/Tubing":
"To insure that the threads are properly engaged, the coupling should be made up hand-tight, then wrench tightened. Generally, wrench-tightening should not exceed three additional threads. It should never be necessary to use an extension handle on a wrench to make up a tight joint."
and..
"Threaded openings where these fittings are intended to be used are permitted to have either tapered (NPT) or straight (NPS) threads. Care should be taken to insure that the threaded entry will accommodate a minimum of 3 full engaged threads of the fitting."
UL also has a table in the RMC specification - UL6, which specifies the correct pitch and effective length of cut threads. These all vary by trade size.
I concur with the STI's suggestion. As a rule of thumb, I would have a minimum of 3 full threads inside a fitting or hub - not only for mechanical, but electrical and environmental purposes. Any less than that, (even though it looks fine), you may be on the hairy edge of the fitting thread tolerances.
NEC 344.28 suggests in the FPN that the threads should be recut the same as the manufacturer supplied threading, Also, cutting too many threads will also cause a weak joint and poor grounding continuity.
I believe this is more of a workmanship issue, rather than a specific NEC requirement.
Hope that helps.
"To insure that the threads are properly engaged, the coupling should be made up hand-tight, then wrench tightened. Generally, wrench-tightening should not exceed three additional threads. It should never be necessary to use an extension handle on a wrench to make up a tight joint."
and..
"Threaded openings where these fittings are intended to be used are permitted to have either tapered (NPT) or straight (NPS) threads. Care should be taken to insure that the threaded entry will accommodate a minimum of 3 full engaged threads of the fitting."
UL also has a table in the RMC specification - UL6, which specifies the correct pitch and effective length of cut threads. These all vary by trade size.
I concur with the STI's suggestion. As a rule of thumb, I would have a minimum of 3 full threads inside a fitting or hub - not only for mechanical, but electrical and environmental purposes. Any less than that, (even though it looks fine), you may be on the hairy edge of the fitting thread tolerances.
NEC 344.28 suggests in the FPN that the threads should be recut the same as the manufacturer supplied threading, Also, cutting too many threads will also cause a weak joint and poor grounding continuity.
I believe this is more of a workmanship issue, rather than a specific NEC requirement.
Hope that helps.
technoid52
Member
- Location
- PA
When I use to install rigid conduit we would tighten with a pair of 18's. Just a bit past snug tight. We used tapered dies. If you could not rock the pipe in the coupling it was good to hang.
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