EMT Connectors to Rigid Couplings or Hubs

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jckenner

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There have recently been several questions in the CQD (Charlie Trout) that discuss using fitting connectors (EMT, flex, sealtite), which normally have untapered threads, with rigid couplings, which have tapered threads. Someone from UL wrote in that fittings are only evaluated by UL in sheetmetal enclosures with locknuts. They are not listed for use with rigid couplings or hubs. The primary reason given is that they will not mate for a moisture tight connection, but also that they may possibly not assure an effective ground path. In any case, fittings are not listed for use with threaded hubs, which includes Meyers hubs, condulets, Bell and other cast boxes.

This is making me feel like the days of the double nickle speed limit, when any car could be pulled over at any time because everyone broke the speed limit. If people can afford to pay electricians to pipe everything in GRC great, but as things stand virtually every installation I see is in violation. What am I missing here? Are manufacturers going to begin to manufacture tapered thread fittings and list them for use in hubs?
 
e57

e57

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OK... I'm a little lost on this - most HUBS are tappered... i.e. they tighten before they bottom out... It'll happen with straight or like threads of male threads - tapered or straight. On the other hand - RMC couplings are straight through?

As far as I know - they all share the same listing... ????
 
kbsparky

kbsparky

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Electrical threaded rigid couplings are not taper threaded.
Rigid pipe has tapered male threads, but since the couplings are straight threaded, it is not water-tight, even when made up wrench-tight.

Plumbing threaded couplings are taper threaded.
 
don_resqcapt19

don_resqcapt19

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kbsparky said:
Electrical threaded rigid couplings are not taper threaded.
Rigid pipe has tapered male threads, but since the couplings are straight threaded, it is not water-tight, even when made up wrench-tight.

Plumbing threaded couplings are taper threaded.
Click to expand...
And rigid conduit used with a conduit coupling is not water tight even when made up wrench tight.
 
don_resqcapt19

don_resqcapt19

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It is UL's position that no conduit or cable connector has been tested for use with couplings or hub..they are only tested for use with locknuts.

The point about using a bell box is a good one...it appears, according to UL, that bell boxes can only be used with threaded rigid conduit.

It is time that UL gets into the real world. Conduit, including flexible conduit, connectors are extensively used with hubs and or couplings in the field without any problems.

As far as the grounding path, UL tells us that reducing washers are suitable to maintain that path, so if their tests can actually prove that, I can't see how the same method of testing would not prove that a threaded connector used with a coupling or hub is a suitable ground path.
 
J

jckenner

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OK, you all are right that electrical rigid cups are straight thread (NPS) rather than tapered (NPT). This is why a piece of running thread (NPS) threads right through a rigid coupling. I was quoting another post and the logic they were presenting without thinking it through. I think all fittings are also NPS. At least some of the bell boxes, and all of the cast iron boxes and codulets I have on the shelf appear to be NPS. All male fittings which includes connectors as well as chase and offset nipples are all NPS.

There is bad information out there on this subject from people who should know better. The IAEI magazine online has a post by UL that says "All hubs are intended for use with threaded conduit, not fittings. Hubs are provided with a tapered thread, and so is threaded conduit ..." This post goes on to tells us that this is why EMT into a hub is not watertight, etc. I agree with them (and you all) that this connection isn't watertight, but their assertion that the hubs are tapered is not correct (at least not universally).


I understand that UL only tests things that manufacturers are willing to pay them to evaluate, but this is a crazy hole in the code, that we are directed to use listed installations and these everyday installations that we build are not listed systems. I know that when I make up one of my installations wrenchtight, I've got an excellent ground return path. When I need something watertight, like on a rooftop, I confess I resort to silicone on the outside, no matter what parts I've used. I guess I'll continue to be an outlaw.
 
e57

e57

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jckenner said:
Funny, maybe TnB has listed these installations, but the IAEI post from UL that I quoted specifically dismisses the TnB type of watertight EMT fitting.

http://www.iaei.org/magazine/?p=1556
Click to expand...
I'm gonna have to agree with Don in the statement below... As opposed to un-named UL writer - who may not have ever seen an EMT fitting outside of a drawing of one in his office on a screen....



don_resqcapt19 said:
It is time that UL gets into the real world. Conduit, including flexible conduit, connectors are extensively used with hubs and or couplings in the field without any problems.
Click to expand...

As for rain-tightness requirements - IMO they have been pushed to a limit that has expanded year by year depending on manufacturer initiated mandate of thier own product... For example I have a bucket of previously 'rain-tight' fittings that are only 'rain-tight' now if thown across the Canadian border... :roll:

As for grounding - IMO - it makes little difference.... - If anything - makes it better.... By forcing deformation of the male threads at the bottom of the female threads - even if they were straight to straight either the end or shoulder will butt to box or connector - making it no different than if in a sheet metal box. Even if there is a rubber gasket - as required for RT fittings - what is different than the tightness of that application in a hub - as opposed to a sheet metal box. Deformation of the gasket is the same at the degree of tightness... Due to the thread mashing - it's BETTER... JMSO.
 
don_resqcapt19

don_resqcapt19

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jckenner said:
OK, you all are right that electrical rigid cups are straight thread (NPS) rather than tapered (NPT). This is why a piece of running thread (NPS) threads right through a rigid coupling. I was quoting another post and the logic they were presenting without thinking it through. I think all fittings are also NPS. At least some of the bell boxes, and all of the cast iron boxes and codulets I have on the shelf appear to be NPS. All male fittings which includes connectors as well as chase and offset nipples are all NPS.
...
Click to expand...
As far as I know the female threads on hubs and conduit bodies are all tapered threads.
 
J

jckenner

Member
Don -- You're making me work. You're right that the catalogs say that the hubs are NPT. What I have on the shelf must be sloppy tolerances of cast iron fittings. They accept running thread all the way down, as well as other straight thread fittings. Of course we've all encountered the extent to which you need to try different combinations of male and female threads to get parts that mate properly. This is what we deal with as the industry standard when there are cast parts rather than actually threaded fittings. This is a major reason that things don't thread down watertight, though they certainly seem to mate well enough to give good ground paths. So yes, I stand corrected that hubs are NPT.
 
Y

yired29

Senior Member
e57 said:
I'm gonna have to agree with Don in the statement below... As opposed to un-named UL writer - who may not have ever seen an EMT fitting outside of a drawing of one in his office on a screen....QUOTE]

The un-named UL writer was Tom Lichtenstein.

Tom Lichtenstein is a staff engineer in the Regulatory Services Department of Underwriters Laboratories Inc. As an electrical engineer with UL for more than 14 years, Tom is responsible for supporting the UL Mark and providing support services for regulatory authorities. Tom is also a member of NEC CMP-19, Canadian Electrical Code (CEC) Part 1 Committee associate member, Canadian Advisory Council on Electrical Safety (CACES) and an inspector member of the IAEI.

This is from
http://www.jigsaw.com/scid5591321/tom_lichtenstein.xhtml
Click to expand...
 
e57

e57

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Location
San Francisco, CA
yired29 said:
e57 said:
I'm gonna have to agree with Don in the statement below... As opposed to un-named UL writer - who may not have ever seen an EMT fitting outside of a drawing of one in his office on a screen....
Click to expand...

The un-named UL writer was Tom Lichtenstein.

Tom Lichtenstein is a staff engineer in the Regulatory Services Department of Underwriters Laboratories Inc. As an electrical engineer with UL for more than 14 years, Tom is responsible for supporting the UL Mark and providing support services for regulatory authorities. Tom is also a member of NEC CMP-19, Canadian Electrical Code (CEC) Part 1 Committee associate member, Canadian Advisory Council on Electrical Safety (CACES) and an inspector member of the IAEI.

This is from
http://www.jigsaw.com/scid5591321/tom_lichtenstein.xhtml
Click to expand...

Beat what it may... He needs to get out of the office more - or advocate industry wide change comparable to his opinion... The product matching/mating - one to one - to fit his opinion - just do not exist.... :roll:

More importantly - is it important? In this situation IMO - NO... ;)
 
Y

yired29

Senior Member
e57 said:
Beat what it may... He needs to get out of the office more - or advocate industry wide change comparable to his opinion... The product matching/mating - one to one - to fit his opinion - just do not exist.... :roll:

More importantly - is it important? In this situation IMO - NO... ;)
Click to expand...

I agree with using a rigid coupling as a change over. Unfortunately they are not listed for use with connectors. There are many approved fittings available. Here is a link for RMC to LFMC 1/2" - 4" look at page 46.

http://appletonelec.com/PDF/I-39thru48[1].pdf#I8
 
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jckenner

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Thanks yired, I continue to be amazed by the number of parts that exisist in our industry. So indeed Appleton makes Sealtite fittings that are compliant. Of course, I doubt I'll be special ordering them in the quantities I'll consume, especially at the prices they'd fetch for these "special application" critters (being that almost no one else is using them).

I remain flabbergasted that I'm supposed to be using set screw condulets rather than being able to screw EMT fittings into the threaded style. And the fact that bell boxes aren't to be used with EMT is boffo. I don't know enough about how things work in the product approval end of the business to lay this on UL, the manufacturers, or the appropriate code panels, but this situation is pretty ridiculous. I'd be surprised if as many as 1% of the installations using these products are in compliance. Most electricians are unaware of these issues. The watertightness issue has some validity, but the ground return path integrity issue is only that no one has wanted to pay to test the many combinations. I suspect that I'll continue to do clean and solid installations as I've been doing, and perhaps the industry will figure this all out someday.
 
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