250.92(B) No Standard Locknuts for sole means of bonding

[Gategator37]

A service lateral from a POCO transformer terminates in a meter then from that meter goes to the panelboard. Where the service lateral enters the meter a rigid conduit is used with a locknut on both sides of the meter enclosure. Does this violate 250.92(B)? I would say yes, but it appears that's how some electricians do it and get away with it. I would say even with the (2) locknuts you still need a bonding bushing or a locknut that is rated for bonding (includes a screw). I might be answering my own question as it states plain as day that standard locknuts cannot be the sole means for bonding.

Thanks

 

[infinity]

I agree with you. One bonding locknut is all that's required if the KO is the same size as the conduit, meaning without concentric or eccentric KO's.

 

[augie47]

I concur also

 

[jaggedben]

I agree with you. One bonding locknut is all that's required if the KO is the same size as the conduit, meaning without concentric or eccentric KO's.

I think if you have a 'bonding type locknut' it doesn't matter if the knock-outs are concentric or eccentric? At least in 2011.

Not sure what counts as a 'bonding type locknut' or if I've ever seen one, or if you mean the same thing by 'bonding locknut.' We always use bonding bushings anyway.

 

[hurk27]

I think if you have a 'bonding type locknut' it doesn't matter if the knock-outs are concentric or eccentric? At least in 2011.

Not sure what counts as a 'bonding type locknut' or if I've ever seen one, or if you mean the same thing by 'bonding locknut.' We always use bonding bushings anyway.

A bonding type locknut has a pointed set screw on a little tab the after tightning the locknut then running this screw in tight it digs into the panel metal, while we are allowed to use them when there is no concentric KO's left but many of our inspectors won't allow them when there is, I can't remember some of the discussion when this section was changed back in 2002 from the 99 NEC, but I remember UL had a lot of input over this and was centered around the issue with concentric or eccentric KO's not meeting connection requirment with regular locknuts, but when there were no concentric or eccentric they were ok, if you look at 250.92(B)(3) it clearly allows threadless RMC connections without a grounding bushing or locknut as long as there are no concentric or eccentric KO's left, but again this statment:

Standard locknuts or bushings shall not be the sole means for the bonding required by this section.

seems to even require bonding if threadless connectors are used, which seems to trump 250(B)(3) if it wasn't ment to only be required around concentric or eccentric KO's, I remember something back then about knocking out all the concentric or eccentric KO's then use reduceing washers, and UL said they are compliant for grounding, which really put a spin on this subject, I think Don had a good post about this subject about this time (2002 code cycle) that followed along the same lines.