Lock Nuts

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ceb58

ceb58

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Raeford, NC
I looked at a job today where the installers used only the grounding bushing to connect to the chase nipples from LB's coming into the boxes. The connections were tight but am I wrong in thinking there should have been a lock nut then the grounding bushing?
 
ceb58 said:
I looked at a job today where the installers used only the grounding bushing to connect to the chase nipples from LB's coming into the boxes. The connections were tight but am I wrong in thinking there should have been a lock nut then the grounding bushing?
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Curtis, I agree with Larry and will look for the code section that permits it.

Roger
 
roger said:
Curtis, I agree with Larry and will look for the code section that permits it.

Roger
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Good luck finding that one, I don't think the code comments on the number of lockouts required.
 
acrwc10 said:
Good luck finding that one, I don't think the code comments on the number of lockouts required.
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Not a problem, it's not specific to locknuts but I have posted it before just couldn't remember the section off the top of my head.

300.4 G, note the wording, it only prohibits bushings made of insulating material from being the sole means of connection, metal bushings that securely fastens the conduit to the box are not prohibited. I think Mike had a graphic and commentary at one time.

Conduit bushings constructed wholly of insulating material
shall not be used to secure a fitting or raceway. The insulating fitting
or insulating material shall have a temperature rating not less
than the insulation temperature rating of the installed conductors.
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There would have to be at least one locknut or some type of shoulder on the back side though.

Roger
 
roger said:
300.4 G, note the wording, it only prohibits bushings made of insulating material from being the sole means of connection, metal bushings that securely fastens the conduit to the box are not prohibited. I think Mike had a graphic and commentary at one time.
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It was very common when installing mud boxes in poured concrete with RMC to install a metal bushing inside the box and a single locknut on the outside of the box. In those installations you still ended up with at least one locknut when connecting to the box.
 
I just saw (new to me) a gounding locknut that has a terminal same as bushing but has the ridgeing that the Locknut has on it unlike the bushing has no locking ridges. This one made by Bridgeport. The bushing part comes off to tighten nut.
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Unless you are using threaded conduit and can get a little extra thread into your enclosure, it isn't all that often there is enough thread for a second locknut. Cinching it tight shouldn't be all that important - bonding is being achieved by tightening the set screw on the bushing more so than by tightening of "the locknut". Remember you were using a bonding bushing because improved bonding was necessary in the first place.

I have used bonding bushings when entering a non metallic enclosure at times - those often have thicker walls and no way you are getting a second locknut on a fitting with fixed amount of threads. Same applies, the set screw and a bonding wire is the reason you used the bonding bushing in the first place.
 
kwired said:
Unless you are using threaded conduit and can get a little extra thread into your enclosure, it isn't all that often there is enough thread for a second locknut. Cinching it tight shouldn't be all that important - bonding is being achieved by tightening the set screw on the bushing more so than by tightening of "the locknut". Remember you were using a bonding bushing because improved bonding was necessary in the first place.
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Have you never used metallic bushings that are not bonding bushings? They used to be somewhat common and are still made.

Roger
 
roger said:
Have you never used metallic bushings that are not bonding bushings? They used to be somewhat common and are still made.

Roger
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OP was asking about grounding bushings, but yes I have seen them on existing installations, mostly use old ones I have removed as temporary bushings while pulling so don't get rope/string burn through on a PVC TA or on the plastic bushing. Helpers never pull straight out they pull against the side wall of fittings and burn through them with pull rope.

I question if code recognizes them anymore though, unless they would have an insulated throat. Would have to double check but seem to recall there is wording in there about insulating material.
 
kwired said:
I Iuestion if code recognizes them anymore though, unless they would have an insulated throat. Would have to double check but seem to recall there is wording in there about insulating material.
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That's for #4 and larger conductors.
 
ceb58 said:
I looked at a job today where the installers used only the grounding bushing to connect to the chase nipples from LB's coming into the boxes. The connections were tight but am I wrong in thinking there should have been a lock nut then the grounding bushing?
Click to expand...
infinity said:
IMO the chase nipple requires a locknut.
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Had to be a close nipple or other short length of conduit. How do you put a bushing (grounding or not) on a chase nipple that is also threaded into a conduit body?
 
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