Using Rigid coupling for transitioning

[infinity]

Here's the Article referenced in the OP:

http://www.iaei.org/magazine/2012/07/transitioning-between-raceways/

It's funny that this was written by a fitting manufacturer yet they do not make a listed fitting for these common transitions.

 

[iwire]

Here's the Article referenced in the OP:

http://www.iaei.org/magazine/2012/07/transitioning-between-raceways/

It's funny that this was written by a fitting manufacturer yet they do not make a listed fitting for these common transitions.

Issues like this really make me question ULs and manufacturers credibility.


For example, this is considered fine for grounding

But the article questions the effectiveness of a RMC coupling to carry fault current.

 

[George Stolz]

Most of those fittings are not made in larger sizes so you rigid coupling transition is the only option.

I don't lose sleep over it:

90.4 Enforcement. This Code is intended to be suitable for mandatory application by governmental bodies that exercise legal jurisdiction over electrical installations, including signaling and communications systems, and for use by insurance inspectors. The authority having jurisdiction for enforcement of the Code has the responsibility for making interpretations of the rules, for deciding on the approval of equipment and materials, and for granting the special permission contemplated in a number of the rules.
By special permission, the authority having jurisdiction may waive specific requirements in this Code or permit alternative methods where it is assured that equivalent objectives can be achieved by establishing and maintaining effective safety.
This Code may require new products, constructions, or materials that may not yet be available at the time the Code is adopted. In such event, the authority having jurisdiction may permit the use of the products, constructions, or materials that comply with the most recent previous edition of this Code adopted by the jurisdiction.

This states that the AHJ may waive requirements, and given the lack of available products then the AHJ has ample legal ground to stand on to ignore aspects of 300.15. People always point to 90.4 when it comes to inspectors making up rules in the field, but it doesn't say that. In fact, it says the exact opposite, that AHJs have permission to ignore the written rules when they see fit.

Not directing this at you, Rob, just your comment was the closest to what I wanted to talk about.

 

[infinity]

This states that the AHJ may waive requirements, and given the lack of available products then the AHJ has ample legal ground to stand on to ignore aspects of 300.15. People always point to 90.4 when it comes to inspectors making up rules in the field, but it doesn't say that. In fact, it says the exact opposite, that AHJs have permission to ignore the written rules when they see fit.

Not directing this at you, Rob, just your comment was the closest to what I wanted to talk about.

Yes, this has been an accepted practice by inspectors for decades around here. Problem now is that more and more jobs have high paid electrical consultants who love to find things that deviate from the letter of the code. Throw in an article by Mark Ode and they'll have you installing a box in lieu of the rigid coupling. :roll:

 

[iwire]

Problem now is that more and more jobs have high paid electrical consultants who love to find things that deviate from the letter of the code. Through in an article by Mark Ode and they'll have you installing a box in lieu of the rigid coupling. :roll:

Or even EIs that are afraid to deviate from what they read in IAEI mags.

 

[K8MHZ]

Issues like this really make me question ULs and manufacturers credibility.


For example, this is considered fine for grounding

But the article questions the effectiveness of a RMC coupling to carry fault current.

Your image didn't come through, but would I be making an accurate assumption that you were talking about these:

View attachment 7235

 

[don_resqcapt19]

Your image didn't come through, but would I be making an accurate assumption that you were talking about these:

View attachment 7235

It would be my guess that Bob was talking about reducing washers.

 

[George Stolz]

The text of his link indicated he was referring to 3838AST MC connectors.

 

[iwire]

Thanks George, yes, it was a picture of a duplex MC connector that just pushes into a KO and the MC or AC cable just pushes into it.

 

[fmtjfw]

Meeting the letter of the UL listing (White book DWTT)

Meeting the letter of the UL listing (White book DWTT)

Definitions:
NPT national pipe tapered threads
NPSM national pipe straight mechanical threads

If you want to meet the requirements set forth in the UL listing for conduit fittings to join two different raceways or a raceway and cable and do not have a specific listed fitting to do that, you can do the following:

Use a cable or raceway fitting to female threads, then use a short RMC/IMC nipple*, and finally use another cable or raceway to female threads fitting. What you are doing is using a nipple rather than a coupling.

To connect a non-threaded round raceway to a threaded hub, you also use a raceway to female threads fitting, a RMC/IMC nipple and the threaded hub.

The female threads of fittings are designed to mate with NPT male threads. The male threads of fittings are designed to mate with locknuts and and have NPSM threads. Raceway threading is NPT.

Screwing NPSM male threads into a NPT female socket does not tighten up using the surface of the threads, if it does tighten up it does so by bottoming out or by a lip on the male part striking the outside of the fitting. Either way the connect is not as strong, not as resistant to coming loose, not as effective as current path, and unlikely to be water proof.

*The nipple needs to have NPT and not NPSM. An "all-threads" nipple (2 feet long, cut off chunks as you need them) does not meet the requirements. An NPSM threaded nipple may be used with locknuts and presumably bushings (since the end threads of NPT are essentially NPSM).

 

[renosteinke]

Sierra, FM, .... those are nice tries, but leave the issues uexplained.

"There are reasons ..." More a statement of faith than an explanation.

"Watertight" .... never an issue from an electrical standpoint. NO recognized raceway is intended to be tight against liquid entry, not even the stuff called 'liquitite'. It's not as if the electricity will drip out and form a puddle.

'Taper vs. straight.' Might be time to set aside the Machinery's handbook and look at a stick of rigid. The system is deliberately intended to have straight threads on the couplings and taper threads on the pipe.

Straight to straight? There seems to be no issue with using a chase nipple with a coupling either. The joining threads on unions use straight threads. Many conduit bodies have straight threads, to accept the straight threads of EMT (or MC, or NM) connectors.

Grounding? As others have observed, there are all manner of listed fittings whose connections are far less secure than even the loosest threaded fitting.

That's why I said the UL position is illogical.

 

[kwired]

Sierra, FM, .... those are nice tries, but leave the issues uexplained.

"There are reasons ..." More a statement of faith than an explanation.

"Watertight" .... never an issue from an electrical standpoint. NO recognized raceway is intended to be tight against liquid entry, not even the stuff called 'liquitite'. It's not as if the electricity will drip out and form a puddle.

'Taper vs. straight.' Might be time to set aside the Machinery's handbook and look at a stick of rigid. The system is deliberately intended to have straight threads on the couplings and taper threads on the pipe.

Straight to straight? There seems to be no issue with using a chase nipple with a coupling either. The joining threads on unions use straight threads. Many conduit bodies have straight threads, to accept the straight threads of EMT (or MC, or NM) connectors.

Grounding? As others have observed, there are all manner of listed fittings whose connections are far less secure than even the loosest threaded fitting.

That's why I said the UL position is illogical.

:thumbsup::thumbsup:

When you use a 10-32 ground screw it is also straight thread screw threaded into straight thread hole.