teflon tape on conduit threads.

[reyamkram]

I came in to work and found, this see pictures, I do not believe this is right, and I believe will interfere with the ground fault current path.
I would like to know some opinions on that matter, because I would like to bring it up to the AHJ. it is a hazardous location, Class 1 division 1,
we have flammable vapor gases.

Any help and information, thank you.
reyamkram.

 

[drcampbell]

In practice, the contact pressures on tapered threads that are drawn up tight will usually be high enough that you'll end up with metal-to-metal contact, despite starting with a few wraps of PTFE tape.

But you're right; it shouldn't be there. The threads should be assembled dry. A metallic anti-seize compound would be acceptable, but isn't necessary.

 

[rbalex]

This was discussed in some detail here.

 

[ptonsparky]

This was discussed in some detail here.

Post 7 in particular.

 

[kwired]

In practice, the contact pressures on tapered threads that are drawn up tight will usually be high enough that you'll end up with metal-to-metal contact, despite starting with a few wraps of PTFE tape.

But you're right; it shouldn't be there. The threads should be assembled dry. A metallic anti-seize compound would be acceptable, but isn't necessary.

Threads on raceway fittings are part of the pressure relief design for explosion proof applications, using anything on threads that would effectively seal those threads inhibits this ability. When an explosion does occur within raceway and/or associated enclosures the hot gases of that explosion are forced through the threads and spiral around the circumference of the threaded joint, cooling them as it travels this path. By the time it reaches the outside atmosphere (which may may contain easily ignitable gases) it will be cooled enough it won't be an ignition source. Anti-seize compounds will also effectively create a seal that is not desired here.

 

[don_resqcapt19]

... Anti-seize compounds will also effectively create a seal that is not desired here.

At least one of the approved corrosion resistant compounds required by 300.6(A) for field cut threads appears to be almost identical to copper never-seize.

 

[kwired]

At least one of the approved corrosion resistant compounds required by 300.6(A) for field cut threads appears to be almost identical to copper never-seize.

I dunno, kind of goes against what I have been taught where part of reasoning for threaded assembly of components, not just raceways, but same goes for threaded box or conduit body covers as well. Then the bolt on covers that have machined mating surfaces supposedly have similar function. They have somewhat wide flat machined surface, no gasket or sealers are used because when an explosion occurs pressure escapes through what little gap is between surfaces but escaping gases are cooled sufficiently passing through that wide mating surface area so there is no threat when they exit.

That is what I remember learning about this kind of equipment long ago

 

[tom baker]

At least one of the approved corrosion resistant compounds required by 300.6(A) for field cut threads appears to be almost identical to copper never-seize.

And my brother in law, who was an airframe mechanic, said they had a very similar product for planes

 

[sameguy]

Ground plane ( not equip. ground) and threads for control of the gas.

The evolution of the Ex-proof flame path | Cortem S.p.A.

www.cortemgroup.com

 

[bobgorno]

Great memory rbalex, referring back to a 2009 thread.

Teflon tape on conduit threads means a plumber did the install, not a real electrician. It’s probably not your only problem.

Does the NEC HB still address the issue in the commentary? See post #16 at rbalex link.


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