250.102

[travis301]

My question is this,when installing an equipment bonding jumper on the service supply side to bond the metal conduit to the GEC terminal the code says to use Table 250.66. The code also states the bonding jumper can be a wire,bus,screw or other suitable conductor.Why wouldnt you use a grounding bushing on the conduit with a set screw binding into the metal enclosure versus a wire sized off of the table taken to a grounding bushing on the conduit with a lug for the wire? Same question on the load side only Table 250.122 shall be used.
Seems to me this would be a lot cheaper install,but probably not better. What am I missing?

 

[suemarkp]

Because if you have concentric knockouts, you can't just screw to the enclosure. If you have a correctly sized knockout, then the locknuts with the piercing bonding screw are probably your cheapest and easiest solution.

I kind of like the looks of the bonding bushings (insulated throat, set screws, and a wire lug), as it appears to be a little more robust.

 

[travis301]

I agree Mark if the KO is the proper size. What I cant fathom is how the NEC can find a screw equivalent to a large conductor as you would have in a large service.

 

[mtnelectrical]

Well I believe when you use concentrics KO there is the possibility of breaking off, That's why the bushing is for to be sure if the ko breaks you still have continuty for the grounding. Now when you use the right size, the locknut make (when is properly tighten) enough contact with the metal box to continue the path for grounding.

 

[infinity]

My question is this,when installing an equipment bonding jumper on the service supply side to bond the metal conduit to the GEC terminal the code says to use Table 250.66. The code also states the bonding jumper can be a wire,bus,screw or other suitable conductor.Why wouldnt you use a grounding bushing on the conduit with a set screw binding into the metal enclosure versus a wire sized off of the table taken to a grounding bushing on the conduit with a lug for the wire? Same question on the load side only Table 250.122 shall be used.
Seems to me this would be a lot cheaper install,but probably not better. What am I missing?

Since when does a bonding bushing on the conduit bind into the metal enclosure? A bonding locknut would do that but not a bonding bushing.

Well I believe when you use concentrics KO there is the possibility of breaking off, That's why the bushing is for to be sure if the ko breaks you still have continuty for the grounding. Now when you use the right size, the locknut make (when is properly tighten) enough contact with the metal box to continue the path for grounding.

A service raceway would still require a bonding locknut, a standard locknut for this application does not satisfy the NEC.

 

[mtnelectrical]

yeah I meant a bonding locknut.Upps

 

[travis301]

Me too.Thanks for clarification