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#205397 - 02/18/12 02:06 AM lock nut 2 or 1  
Niko  Offline
Member
Joined: Aug 2006
Posts: 356
Campbell, CA
How many lock nuts are required at each end of IMC or RMC conduit that enter an enclosure. One outside and one inside of the enclosure or just one inside?

I always have installed 2 (outside and inside), but i vaguely remember that i had read somewhere that only one is required on the inside.

I could be wrong.


Be kind to your neighbor, he knows where you live


2017 / 2014 NEC & Related Books and Study Guides

#205398 - 02/18/12 02:55 AM Re: lock nut 2 or 1 [Re: Niko]  
mikethebull  Offline
Member
Joined: Mar 2007
Posts: 100
Rhode Island
I'm lookin @ 342 & 344 and I don' t seewhere locknuts are required on both sides


#205400 - 02/18/12 03:59 AM Re: lock nut 2 or 1 [Re: Niko]  
gfretwell  Online Content


Member
Joined: Jul 2004
Posts: 9,123
Estero,Fl,usa
You may be thinking about this

Quote

250.97 Bonding for Over 250 Volts.
For circuits of over 250 volts to ground, the electrical continuity of metal raceways and cables with metal sheaths that contain any conductor other than service conductors shall be ensured by one or more of the methods specified for services in 250.92(B), except for (B)(1).

Exception: Where oversized, concentric, or eccentric knockouts are not encountered, or where a box or enclosure with concentric or eccentric knockouts is listed to provide a reliable bonding connection, the following methods shall be permitted:

(2) Two locknuts, on rigid metal conduit or intermediate metal conduit, one inside and one outside of boxes and cabinets


Some inspectors want this whenever the raceway is the sole bonding means on any line voltage circuit.


Greg Fretwell

#205402 - 02/18/12 04:59 PM Re: lock nut 2 or 1 [Re: Niko]  
HotLine1  Offline


Member
Joined: Apr 2002
Posts: 6,872
Brick, NJ USA
Am I missing something? Installing IMC/RGC into an enclosure, IF you don't have a locknut on the outside what prevents the raceway from falling into the enclosure?



John

#205403 - 02/18/12 06:34 PM Re: lock nut 2 or 1 [Re: HotLine1]  
Niko  Offline
Member
Joined: Aug 2006
Posts: 356
Campbell, CA
Originally Posted by HotLine1
Am I missing something? Installing IMC/RGC into an enclosure, IF you don't have a locknut on the outside what prevents the raceway from falling into the enclosure?


the straps and the other end of the conduit that is held in place by one locknut in the interior of the other box.

don't get me wrong i always install 2, but was just wondering if it is a code issue or UL issue to have only one.


Be kind to your neighbor, he knows where you live


#205410 - 02/18/12 10:12 PM Re: lock nut 2 or 1 [Re: Niko]  
George Little  Offline
Member
Joined: Jan 2004
Posts: 1,489
Michigan USA
The words in 300.10 Make it very hard to install RMC or IMC using only one locknut (assume it's not a bonding locknut) and maintain continuity of the grounding conductor if the raceway is the grounding conductor. I would not approve an installation of RMC or IMC using a single standard locknut on the inside of an enclosure and nothing on the outside.



300.10 NEC 2008 Edition

Last edited by George Little; 02/18/12 10:13 PM. Reason: Typo

George Little

#205411 - 02/18/12 10:22 PM Re: lock nut 2 or 1 [Re: Niko]  
HotLine1  Offline


Member
Joined: Apr 2002
Posts: 6,872
Brick, NJ USA
George:

This part will work for me.

From 300.10 (2011)
"....shall be mechanically secured to boxes, fittings,
cabinets, and other enclosures."

Niko:
Using your scenario above, it sounds like a heck of a lot of work to save 2 locknuts. I have to say, I have not had anyone try that kind of install.

Could you apply the same mechanical logic with EMT fittings, without locknuts inside the boxes, and the shoulder of the connectors making contact??





John

#205412 - 02/18/12 11:48 PM Re: lock nut 2 or 1 [Re: Niko]  
Tesla  Offline
Member
Joined: Jun 2004
Posts: 1,273
Sacramento, CA
GRC needs two (2) locknuts at each connection, unless the terminus is hubbed.

And don't forget your ( plastic ) bushings, too. I'm amazed at how often they're forgotten.

( GRC nipples require bushings across the entire range of wire sizes. 344.46 )

This also applies to running threads.

-------

That you are even spending one second on this line of inquiry -- is a miss-application of time.

One does NOT make it in the trades by trying to value engineer out locknuts.

It is in the nature of the beast that electrical contractors always have a surfeit of said locknuts since so many connectors end up terminating in PVC female adapters. ( F/As )

Hence, locknuts hold nothing but Scrap Value -- particularly now that China is exporting steel fittings on the cheap.


Tesla

#205413 - 02/19/12 05:51 AM Re: lock nut 2 or 1 [Re: Niko]  
Niko  Offline
Member
Joined: Aug 2006
Posts: 356
Campbell, CA
Guys dont get me wrong i always install outside and inside. furthermore i agree it would be a waste of time as tesla said.

I also agree what 300.10, but if a single lock nut is used and the conduit is secured then i can't fail the inspections.



Be kind to your neighbor, he knows where you live


#205414 - 02/19/12 01:19 PM Re: lock nut 2 or 1 [Re: Niko]  
gfretwell  Online Content


Member
Joined: Jul 2004
Posts: 9,123
Estero,Fl,usa
Quote
if a single lock nut is used and the conduit is secured then i can't fail the inspections.


Sure you can. "secured" is one of those terms that end up being defined by the AHJ. They could easily call this "loosely jointed" and want to see bonding jumpers with bushings. Lock nuts are cheap, Use 2 and make everyone happy.


Greg Fretwell

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