The Electrical Contractor Network

ECN Electrical Forum
Discussion Forums for Electricians, Inspectors and Related Professionals

Books, Tools and Test Equipment for Electrical and Construction Trades

Register Now!

Register Now!

We want your input!

Featured:
   

2017 NEC and Related
2017 NEC
Now Available!

   
Recent Posts
breaker meltdown
by sparky
Yesterday at 07:30 PM
230 or 345 kV transmission lines?
by Vlado
09/24/16 09:33 AM
Electrical mast flashing product
by ThomasWinfrey
09/22/16 12:14 AM
What estimating software do you recommend?
by sparky
09/21/16 07:20 PM
"Dry Run" Inspection goes awry
by HotLine1
09/20/16 07:39 PM
New in the Gallery:
12.5A through 0.75mm˛ flex (just out of curiosity)
Shout Box

Top Posters (30 Days)
HotLine1 14
sparky 10
gfretwell 8
sparky66wv 8
Vlado 6
Who's Online
0 registered (), 209 Guests and 5 Spiders online.
Key: Admin, Global Mod, Mod
Page 1 of 2 1 2 >
Topic Options
Rate This Topic
#205397 - 02/17/12 10:06 PM lock nut 2 or 1
Niko Offline
Member

Registered: 08/17/06
Posts: 358
Loc: 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


Top
2014 / 2011 NEC & Related Books and Study Guides
#205398 - 02/17/12 10:55 PM Re: lock nut 2 or 1 [Re: Niko]
mikethebull Offline
Member

Registered: 03/18/07
Posts: 101
Loc: Rhode Island
I'm lookin @ 342 & 344 and I don' t seewhere locknuts are required on both sides

Top
#205400 - 02/17/12 11:59 PM Re: lock nut 2 or 1 [Re: Niko]
gfretwell Offline

Member

Registered: 07/20/04
Posts: 9012
Loc: 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

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

Member

Registered: 04/03/02
Posts: 6785
Loc: 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

Top
#205403 - 02/18/12 02:34 PM Re: lock nut 2 or 1 [Re: HotLine1]
Niko Offline
Member

Registered: 08/17/06
Posts: 358
Loc: 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


Top
#205410 - 02/18/12 06:12 PM Re: lock nut 2 or 1 [Re: Niko]
George Little Offline
Member

Registered: 01/18/04
Posts: 1492
Loc: 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


Edited by George Little (02/18/12 06:13 PM)
Edit Reason: Typo
_________________________
George Little

Top
#205411 - 02/18/12 06:22 PM Re: lock nut 2 or 1 [Re: Niko]
HotLine1 Offline

Member

Registered: 04/03/02
Posts: 6785
Loc: 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

Top
#205412 - 02/18/12 07:48 PM Re: lock nut 2 or 1 [Re: Niko]
Tesla Offline
Member

Registered: 06/16/04
Posts: 1280
Loc: 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

Top
#205413 - 02/19/12 01:51 AM Re: lock nut 2 or 1 [Re: Niko]
Niko Offline
Member

Registered: 08/17/06
Posts: 358
Loc: 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


Top
#205414 - 02/19/12 09:19 AM Re: lock nut 2 or 1 [Re: Niko]
gfretwell Offline

Member

Registered: 07/20/04
Posts: 9012
Loc: 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

Top
Page 1 of 2 1 2 >



ECN Electrical Forums - sponsored by Electrical Contractor Network - Electrical and Code Related Discussion for Electrical Contractors, Electricians, Inspectors, Instructors, Engineers and other related Professionals