Double locknut

[guschash]

I have question on where to find ,( I don’t know how to describe what I want to ask). When I was apprentice I learned how build, assemble, and mount cabinets ,panels, QMB cabinets etc. Learned what were j-box, short and longs nipple and all aspects Learning constructions jobs. Well yesterday I when with engineer to see the work being done on a traffic lighting control box and I the electrician said the inspector make him put locknut on each side of panel. There were the main breaker panel and a nipple to the main disconnect. Nipple was 6-8 ins. Now my question is there a book that how do things like this? Put a locknut on inside of panel and on the outside. Is it code if so where do I find it.

 

[LarryFine]

Unless there is a connector or a threaded hub, how else could you connect a conduit to a box?

Two lock-nuts have always been the standard way to attach threaded conduit to an enclosure.

 

[xformer]

IMHO... 300.10. But someone might chime in with a better one.

 

[guschash]

I would think the electrician should of learned this when he was in his apprentice program.

 

[xformer]

I would think the electrician should of learned this when he was in his apprentice program.

Well nobody has the codebook memorized. At least no one I have met so far.

 

[xformer]

Could also use 250.4(A)(4)

 

[garbo]

NEC Section 300.10 Electrical Continuity of metal Raceway & Enclosures. Metal raceways, cable armor & other metal enclosures for conductors shall be mechanically joined together into a continuous electrical conductor so as to provide effective electrical continunity. We either used a locknuts on both sides of a nipple or rigid heavy wall or IMC when entering panels pull boxes etc. Had some coworkers use Thomas & Betts metal bushing on the inside of panels without using a locknut. Think T&B part # is 1222 for 1/2" size. They made them in steel & aluminum. Was never sure if that was approved so I always used a locknut on both sides. When you purchase locknuts by the box they are inexpensive.

 

[infinity]

Back in the day we use a steel bushing on the inside and a single lock nut on the outside with RMC.

 

[roger]

Now my question is there a book that how do things like this? Put a locknut on inside of panel and on the outside. Is it code if so where do I find it.

Exception #2 to 250.97, 550.15(F), and 551.47(B)

 

[guschash]

Thanks for all the replies. Found what I was looking for in 250.97exception #2. Thanks Roger.

 

[Eddie702]

Doesn't 250.97 apply only if over 250 volts to ground? 480 etc.

I always thought over 250 to ground two locknuts. Under 250 to ground a metal bushing and a locknut is ok. Has that changed? Can't find in the code where they tell you what to do under 250 to ground.

Obviously I am not talking services and two locknuts is always better