Conduit threading in classified areas

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buddhakii

Senior Member
Location
Littleton, CO
500.8 (E) pretty much says it will be tapered NPT pipe thread.

I disagree. If you are threading conduit into a tapered thread then the conduit does not need to be tapered also. Take a look at 344.42 (b). One of the only place I can picture not being able to get running threads wrench tight is in a coupling. Your qualifier "pretty much" may be taking all of this into account so forgive me if that is the case.
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
I disagree. If you are threading conduit into a tapered thread then the conduit does not need to be tapered also. Take a look at 344.42 (b). One of the only place I can picture not being able to get running threads wrench tight is in a coupling. Your qualifier "pretty much" may be taking all of this into account so forgive me if that is the case.
Conduit threads are required to be tapered.
344.28 Reaming and Threading. All cut ends shall be reamed or otherwise finished to remove rough edges. Where conduit is threaded in the field, a standard cutting die with a 1 in 16 taper (3⁄4 in. taper per foot) shall be used.
The rule you cited does not permit the use of non-tapered threads at fittings.
 

ritelec

Senior Member
Location
Jersey
Don..who are you?..........you seam to know all about all ( I had the tapered thing though......but would not have been able to have sighted the verse so readily).

Kinda reminding me of " The Great and Powerful OZ".................................don't look behind that curtain..............

also I must mention.....you're avatar.....looking hard into it I would think it's a Jacob's ladder or something......but every time I see it it reminds me of Judy Garland or Cindi Lauper.

Thank you for your insight OZ!


Respectfully,
Jack




snubber
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
Don..who are you?..........you seam to know all about all ( I had the tapered thing though......but would not have been able to have sighted the verse so readily).
Just an electrician.
...
also I must mention.....you're avatar.....looking hard into it I would think it's a Jacob's ladder or something......but every time I see it it reminds me of Judy Garland or Cindi Lauper.
It is a 345 kV air break switch being opened.
http://205.243.100.155/frames/mpg/345kV_SWITCH.MPG
 

Gac66610

Senior Member
Location
Kansas
Don..who are you?........

Kinda reminding me of " The Great and Powerful OZ".................................don't look behind that curtain..............




Respectfully,
Jack




snubber
I think that movie will live on in infamy

Not sure i would like being call ... "the OZ" ... after all he was a fake .. all smoke and mirrors ;)
 

K8MHZ

Senior Member
Location
Michigan. It's a beautiful peninsula, I've looked
Occupation
Electrician
You are correct, but how can a running thread be usefull at a box or fitting?

I didn't say anything about useful. How could it be useful in a coupling, the only instance mentioned?

Where would a running thread be useful at all? Remember, the paralell part of the thread will be small in diameter and makes for a sloppy fit.

I have seen guys try to use them for close nipples because they didn't know how to make them with tapered threads.
 

rbalex

Moderator
Staff member
Location
Mission Viejo, CA
Occupation
Professional Electrical Engineer
The key to understanding is found in the second sentence of 500.8(E), ?Conduit and fittings shall be made wrenchtight to prevent sparking when fault current flows through the conduit system, and to ensure the explosionproof integrity of the conduit system where applicable.? But ?wrenchtight? presumes the first and last sentences are also true.

Carefully read 50X.30 for each Class. With the lone (and minor) Exceptions in 501.30(B) and 502.30(B), the requirements for Grounding/Bonding in Division 1 and 2 is the same per each Class. Note the bonding requirements are even to be maintained for Intrinsically Safe installations. (See 504.60)

While a straight thread in an NPT threaded entry may be ?wrenchtight? and seem to be 5 threads ?deep? they will have simply bottomed out and not be ?fully engaged?; i.e., full surface to surface contact for 5 threads (or 4-1/2 for listed enclosures). Arcing may still occur at those joints.
 

Smart $

Esteemed Member
Location
Ohio
I didn't say anything about useful. How could it be useful in a coupling, the only instance mentioned?

Where would a running thread be useful at all? ...
Running threads can be used (in violation) in lieu of installing a three-piece coupling ("ericson"). The running threads on one conduit are long enough to screw the coupling on entirely. This is then butted to a second conduit with standard threads, the coupling is spun off the running threads and onto the threads of the second conduit and all is made wrenchtight.
 

K8MHZ

Senior Member
Location
Michigan. It's a beautiful peninsula, I've looked
Occupation
Electrician
Running threads can be used (in violation) in lieu of installing a three-piece coupling ("ericson"). The running threads on one conduit are long enough to screw the coupling on entirely. This is then butted to a second conduit with standard threads, the coupling is spun off the running threads and onto the threads of the second conduit and all is made wrenchtight.

How do you make it wrench tight without the conduits hitting each other inside the coupling? (And making a burr?)
 
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