chase nipples, close nipples, bond bushing

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iwire said:
109879-326-2-electrical-conduit-chase-nipple-rigid-imc-non-insulated-lot-of-37-2.jpg


Often used to run conductors between enclosures that are tightly positioned.

The issue under discussion has to do with the grounding continuity this fitting may have compared to using a 'close nipple' with locknuts on all sides of each enclosure.

Electrical-Rigid-Conduit-Nipple-close-nipple-long.jpg
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OK. I have seen those but not in a long time. Conduit or EMT is not often used here.
 
iwire said:
110.3(B) and ULs position that they can't say untested combinations meet the listing requirements.

Certainly an AHJ can choose to accept it, they can just as easily fail you for it.

So if you had an AHJ fail your job based on this issue what would your response be?
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Again, note that I am specifically talking about the tapered to non tapered "issue", and not general manufacturers instructions or listings. There is no code that states that thread taper types must match. As far as I know there are no manufactures instructions that say, ".....this is to be used only with XXX conduit because the thread taper type must match ." This issue seems to be fabricated. In the link posted, the author offers no evidence other than just stating that there is an issue (yes he apparently works for UL).

If and AHJ said, "you cant do XXX because the thread taper types dont match" I would ask for a code reference requiring that thread types match. IF he came back with 110.3(B) I would ask what manufacturer or listing document says thread types must match and how why RGS is exempt from that.
 
electrofelon said:
1. There is no code that states anything about tapered mating with non tapered
2. RGS couplings are not tapered.
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The referenced article addresses an issue of a straight thread being inserted into a taper threaded hole of a watertight hub - a straight thread typically jams before it is fully seated, which may compromise the connection.

Your rigid coupling reference involves a taper thread being inserted into a straight thread hole - jamming before being seated typically does not occur.
 
jim dungar said:
The referenced article addresses an issue of a straight thread being inserted into a taper threaded hole of a watertight hub - a straight thread typically jams before it is fully seated, which may compromise the connection.

Your rigid coupling reference involves a taper thread being inserted into a straight thread hole - jamming before being seated typically does not occur.
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The "issue" seems to be when straight male threads are installed in straight female threads.

There is no issue when tapered male threads are in straight female threads, as that is how RMC couplings work with RMC.
Or when tapered male threads are in tapered female threads, like RMC in a Myers hub.

But when straight male threads are installed in straight female threads, there is an issue? I understand that you loose your waterproofing, but if you do this in a dry location or have a gasket, I don't see how it continues to be a problem.
 
Carultch said:
... if you do this in a dry location or have a gasket, I don't see how it continues to be a problem.
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Typically a straight threaded fitting, like a chase nipple or an EMT connector, have a 'shoulder' that is intended to make contact with the enclosure wall. If there is no contact, are the jammed threads sufficient to carry fault currents? We don't know they haven't been tested.
 
jim dungar said:
Typically a straight threaded fitting, like a chase nipple or an EMT connector, have a 'shoulder' that is intended to make contact with the enclosure wall. If there is no contact, are the jammed threads sufficient to carry fault currents? We don't know they haven't been tested.
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And a manufacturer's statement that combination X has not been UL tested should carry a lot more weight than a statement that combination X should not be used because we do not like it.

NEC may not make any explicit statements about thread types, but if a code section requires a listed fitting, it seems to strongly imply that such fitting must be used according to its listing conditions.
 
Carultch said:
The "issue" seems to be when straight male threads are installed in straight female threads.
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To me the only issue is one of testing and listing having to be put in front of commonsense. Most all of us use fittings in ways they were not specifically tested for and the sky has not fallen.

Another example is the hardware that comes with light fixtures, ULs position is we have to use what comes with the fixture. Usually it is undersized machine screws made of butter and wirenuts entirely out of plastic. Putting commonsense behind listing and labeling.

OK, rant done.
 
jim dungar said:
The referenced article addresses an issue of a straight thread being inserted into a taper threaded hole of a watertight hub - a straight thread typically jams before it is fully seated, which may compromise the connection.

Your rigid coupling reference involves a taper thread being inserted into a straight thread hole - jamming before being seated typically does not occur.
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Respectfully Jim, to me that is more opinion and conjecture that is no backed up by any formal analysis or enforceable code. Sure, from an engineering standpoint, taper to taper is likely the strongest, has even distribution of stress, and in fluid applications is less likely to leak and easier to seal, but I have not seen anything specifically disallowing taper to non-taper joints.
 
electrofelon said:
I have not seen anything specifically disallowing taper to non-taper joints.
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Which is precisely what a standard RMC coupling on RMC is.

The reverse situation is more interesting. A straight connector on a threaded boss or hub. This catalog page suggests this practice, and even mentions omitting the gasket, when threading it onto a tapered opening. I would still put the gasket on anyway:
http://tnblnx3.tnb.com/emAlbum/albums/us_resource/gm8249_tc1.pdf

"In some jurisdictions, sealing gaskets are notrequired when installed in a threaded opening"
 
I did find these printed instructions, it looks like NEMA FB-1 may have the answer.
It appears jammed threads are not a general problem, once 3 full threads have been made up.
"EMT connectors are permitted to be assembled into threaded entries of boxes, conduit bodies or internally threaded fittings having tapered threads (NPT). EMT fittings designed to NEMA FB 1 “Fittings, Cast Metal Boxes, and Conduit Bodies for Conduit and Cable Assemblies,” have straight threads (NPS). 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." http://catvanloi.com/edoc/files/Guidelines of using galvanized steel conduit and GI conduit.pdf



 
UL clearly states:

All male threaded fittings and nipples have only been investigated for use with locknuts.

Fittings with internal female threads (e.g., hubs, conduit bodies, couplings) have only been investigated for use with threaded rigid conduit.


Also, all of the conduit body manufacture datasheets that I've seen state that their threaded conduit bodies are for RMC or IMC only. EMT style are threadless with a setscrew.
 
lauraj said:
UL clearly states:

All male threaded fittings and nipples have only been investigated for use with locknuts.

Fittings with internal female threads (e.g., hubs, conduit bodies, couplings) have only been investigated for use with threaded rigid conduit.
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Other than "nipples" (that doesn't make sense assuming they are talking about RMC), I don't disagree. IMO this is one of the most ridiculous things in the electrical world that some of these super common fitting combinations are used and accepted nearly universally but are technically not allowed.

Also, all of the conduit body manufacture datasheets that I've seen state that their threaded conduit bodies are for RMC or IMC only. EMT style are threadless with a setscrew.
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There are "combination" types that are threaded and have setscrews and are suitable for both emt and RMC/IMC.
 
lauraj said:
Also, all of the conduit body manufacture datasheets that I've seen state that their threaded conduit bodies are for RMC or IMC only. EMT style are threadless with a setscrew.
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Did you see the manufacturers quote I cited in post #32.
It says nothing about the actual UL test procedures, but it does say that NEMA standards allow straight male threads to be inserted into tapered hubs.
 
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