Emt fittings

[jim dungar]

Several posts have had Don mentioning an article by UL stating that EMT fitting are only designed for use with lock nuts. For those that are the article can be found at http://www.ul.com/regulators/mayjune2006.pdf

However, there is no mention of "flex" connectors.

edit: Also note, that UL does not say straight threads cannot be used with tapered hubs, just that they have not been evaluated for that purpose. Acceptability is up to the AHJ.
also tried to fix link

 

[LarryFine]

Several posts have had Don mentioning an article by UL stating that EMT fitting are only designed for use with lock nuts.

How many times have we threaded EMT fittings into conduit bodies?

 

[drg]

Ya thats something I never gave a lot of thought, this is not good, have a 1 1/4" EMT run that I worked on today with LB 's and connectors on them ,Huh.

 

[infinity]

So I guess that metal conduit bodies and EMT in wet locations are no longer permissible.

 

[paul]

I guess along the same thought process as is mentioned in the article you posted, is that GRS couplings are also a straight thread. Therefore, they should not be considered watertight when used with the tapered thread (male end) of the GRS or IMC. Grounding would also be an issue, as well as the other issues that are brought up in the article. We should be using plumbing style couplings (tapered) on all GRC and IMC to insure a proper fit.

I find their logic flawed when they consider one way but not the other.

 

[don_resqcapt19]

Jim,
Thanks for finding the reference. It does not say what I thought it said. It does imply what I thought but does not say it directly.

Other considerations with straight threaded connectors into a tapered threaded hub may be grounding. Depending on the installation of the straight threaded connector into the hub, the contact may not be tight enough to assure an effective groundfault current path. The connection of straight threaded connectors, such as EMT connectors, is not evaluated with hubs as part of their Listing.

Don

 

[Bob NH]

I am skeptical about the idea that you can't get reliable grounding through straight threads. It is inconsistent with what is accepted in other components.

The threads may or may not interfere, but the ground path is a result of the load that will exist on both threads and mechanical stop when adequate torque is applied. A tapered thread will not be a reliable ground it is not torqued to provide the load on the joint.

If you run tapered conduit into a straight threaded coupling and torque it up, either the threads will interfere or the ends will butt together in the coupling putting load on both the threads and the ends of the pipes.

EMT couplings rely on the straight threads of the screw to maintain a load and a ground path between the thread and coupling, and between coupling and EMT.

The locknut on a straight threaded connector going into a box is a straight thread, and it produces the contact load that maintains the ground.

That same connector screwed into a coupling will load the shoulder and the threads, ensuring a ground.

A grounding screw is a straight thread that holds a ground wire terminal against the metal box.

A reliable ground path depends on contact forces and contact forces depend on torquing up the mating parts, whether tapered or straight.

 

[jim dungar]

I find their logic flawed when they consider one way but not the other.

Actually UL does not say there is a problem using a combination of straight and tapered threads. UL simply says they have not been evaluated therefore they can not have an official ruling only an opinion.

An AHJ can easily make a judgement based on their historical evidence.

 

[infinity]

Actually UL does not say there is a problem using a combination of straight and tapered threads. UL simply says they have not been evaluated therefore they can not have an official ruling only an opinion.

An AHJ can easily make a judgement based on their historical evidence.

Around here there would be decades of historical evidence to say that the connection between the two is fine. It's hard to believe that a straight thread made up wrench tight is no good but a reducing washer is OK for bonding.

 

[celtic]

It's hard to believe that a straight thread made up wrench tight is no good but a reducing washer is OK for bonding.

...or even one of these things: