electrofelon
Senior Member
- Location
- Cherry Valley NY, Seattle, WA
Is it acceptable to not tighten a piece of Rigid into a coupling or a myers hub and instead use a locknut tightened against the coupling or hub?
lock nuts on RGS couplings and myers hubs
- Thread starter electrofelon
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Daniel malack
Senior Member
- Location
- Amissville, Virginia USA
I've seen it done on flood lights or fixtures that need to be tightened down for getting the light to shine in a specific direction. Because if you tighten it all the way the fixture would be off angle.
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kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
Good question, one kind of would think to get (reasonable) water tightness you must fully tighten into the fitting, but RMC/IMC aren't exactly water tight in general anyway, but don't tell this to those that thought we needed "raintight" EMT fittings a few years back:blink:
- Location
- New Jersey
- Occupation
- Journeyman Electrician
I don't think that there is any requirement to tighten normal RMC into a coupling. If you spin on an elbow and you cannot turn it enough to get it pointing in the right direction you back it off a 1/4, 1/2, or 3/4 turn.
I'm not an AHJ rep' but I would not accept it without adequate reason. Most instructions including some Code section require threaded fitting be made up wrench tight and also there's 110.3(B) follow the instructions rule. Yes, there are some instances where one cannot make up a joint wrench tight and have the fitting pointing the use-required direction.
To find an actual reason I'd have to go digging (do research) and not feeling up to it at present.
hmy:
To find an actual reason I'd have to go digging (do research) and not feeling up to it at present.
hmy:
electrofelon
Senior Member
- Location
- Cherry Valley NY, Seattle, WA
Right I think you will find that in 250 under service bonding (IIRC) , but nothing in article 344. It could be argued that it is "wrench tight" with a locknut lightening the joint.
... so what is your reason for wanting to do so?
electrofelon
Senior Member
- Location
- Cherry Valley NY, Seattle, WA
Because I tighten the locknut with a wrench...or I tighten the RMC with a wrench and it tightens due to the binding action of the locknut.
That's not what I meant. I know the mechanics of it. I want to know your reason for using a locknut in conjunction with a coupling or hub vs. just the coupling or hub.
electrofelon
Senior Member
- Location
- Cherry Valley NY, Seattle, WA
We have back to back cabinets and the nipple is a little too short. My choice would have been nipple and sealing locknuts, but the client wants myers hubs.
I take it you are using factory nipple. Custom cut nipple would be my preference. Can't imagine you are using threaded conduit just for this tie in. As kwired mentioned, you lose any water resistance by using a locknut as a jam nut.
electrofelon
Senior Member
- Location
- Cherry Valley NY, Seattle, WA
Yes factory nipple. This is 4" and alas we dont have threading equipment for this. I agree it is silly: they want myers but then we have a nipple threading into it which isn't water tight.
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
You should carry 4 inch threader in your personal tool belt at all times
How long of a nipple? You can get a little extra length by using two half length nipples and a coupling... plus it gives you a little extra range on the wrench tight aspect... but the distance must at least accommodate two close nipples and a coupling.
electrofelon
Senior Member
- Location
- Cherry Valley NY, Seattle, WA
it was 8.25 total between, used a 6 inch nipple. Each end went about 3/4" into the hub, but was not tight A 7 probably would have been perfect, but I guess they couldnt find one. They tried two nipples and coupling idea but that was even worse than the 6. Apparently they dont know that you have to put the parts together and take an actual measurement to get the right ones. I could have found a good combination, unfortunately this isnt my job, nor was I in charge of getting the nipples.
al hildenbrand
Senior Member
- Location
- Minnesota
- Occupation
- Electrical Contractor, Electrical Consultant, Electrical Engineer
I infer from your words that this myers hub / nipple assembly is in a "service", and I will just bet it is exposed to weather.
If so, the argument about loosing water tightness because of locknuts is really beside the point as the interior of the raceway is "defined" as a WET location.
Just make sure the assembly drains.
A counter to using a locknut is compliance with...
Grounding continuity of such an assembly has not been investigated by UL (or other NRTL).
And the assembly must meet the requirements of 110.3(B).
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
Now tell that to those that insisted on making/listing what we now call "raintight" EMT fittings.:roll:
Daniel malack
Senior Member
- Location
- Amissville, Virginia USA
Why would a Myers hub be a problem? If you install it correctly! Your point is mute!
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al hildenbrand
Senior Member
- Location
- Minnesota
- Occupation
- Electrical Contractor, Electrical Consultant, Electrical Engineer
Read Article 100 Definition of "Fitting". A locknut is a fitting that is intended to provide "primarily" a mechanical, rather than electrical, function.
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