Bonding Bushings

Status
Not open for further replies.
Dean83169

Dean83169

Senior Member
As far as I can understand, standard locknuts shall be used as a means of ground on the supply side of a service. If you use a rigid nipple with locknuts through self made knockouts do you need or not need bonding bushings? What about using EMT through self made knockouts?
 
Metallic service raceways are required to be bonded at one end, and standard locknuts do not satisfy this requirement. If your KO's are full sized you may use bonding bushings, bonding locknuts or a bonding wedge. Bonding bushings are not your only option.
 
infinity said:
Metallic service raceways are required to be bonded at one end, and standard locknuts do not satisfy this requirement. If your KO's are full sized you may use bonding bushings, bonding locknuts or a bonding wedge. Bonding bushings are not your only option.
Click to expand...

Trevor, we just installed a feeder run in which we discussed where we could use plastic bushings and bonding bushings. I was under the impression that if we had all metallic conduit runs, and the knockouts were not eccentric or coeccentric, we did not have to have a bonding bushing. On the PVC run going to the transformer, we bonded the end at the ct enclosure.

Such as if you used EMT between panels, you put two connectors, say 12" of EMT and plastic bushings. Would you need bonding bushings on this? What about all branch circuit conduits runs, such as 1/2" and 3/4"? I never see any bonding bushings on these conduit runs. I thought the locknut was adequate for grounding on emt, grc and imc.
 
Dean,
250.92(B)(3) Threadless couplings and connectors where made up tight for metal raceways and metal-clad cables
...Standard locknuts or bushings shall not be the sole means for the bonding required by this section.
Click to expand...
It is my opinion that service raceways always require the use of something other than a locknut for bonding the raceway to the enclosure. In the case of a threaded connector, the connector is making the bond between the connector and the raceway and you need a bonding device to make the bond between the connector and the enclosure. If the KO is a clean KO, the bonding device may not require a bonding jumper to make the bond to the enclosure, but if there are any remaining rings of a KO, then a bonding jumper from the bonding device to the enclosure is required.
Don
 
There is a difference between a service raceway, and those for branch circuits.

I believe that only the service raceways, and branch circuit raceways where the voltage to ground exceeds 250 and eccentric or concentric knockouts are encountered require the use of bonding connections.
 
250.92(B) "Method of Bonding at the Service" (2002) says in part that "standard locknuts or bushings shall not be the sole means for the bonding required by this section".

edit: Don beat me to it.
 
But if I knock out the gear for 3", if its fed with 3" EMT from the main MDP will a standard 3" EMT connector, standard locknut and plastic bushing satisfy the NEC or do I need a bonding bushing or any of the methods you decribed above. Also if I add a xformer off this piece of gear to go from 480 to 120/208 do the requirements for bonding change?
 
Last edited:
Dean83169 said:
But if I knock out the gear for 3", if its fed with 3" EMT from the main MDP will a standard 3" EMT connector, standard locknut and plastic bushing satisfy the NEC or do I need a bonding bushing or any of the methods you decribed above.
Click to expand...

Since this is not service equipment, I believe this will satisfy the nec.
 
Dean83169 said:
But if I knock out the gear for 3", if its fed with 3" EMT from the main MDP will a standard 3" EMT connector, standard locknut and plastic bushing satisfy the NEC or do I need a bonding bushing or any of the methods you decribed above. Also if I add a xformer off this piece of gear to go from 480 to 120/208 do the requirements for bonding change?
Click to expand...

As I mentioned in my first post the requirement for other than standard locknuts applies to metallic service raceways. Once you get past the line side of the service disconnect standard locknuts and bushings may suffice.
 
Just to point out also:
1) It is the size of the wire that requires bushings, not the size of the pipe. Just to clarify.
2) Raco boxes with eccentric KOs are specifically listed to fit the exception to bonding over 250V. I'm not sure if other mfgs do the same thing or not.
 
Last edited:
infinity said:
As I mentioned in my first post the requirement for other than standard locknuts applies to metallic service raceways. Once you get past the line side of the service disconnect standard locknuts and bushings may suffice.
Click to expand...

Trevor, are you talking about where you come from the POCO transformer to the main disconnect? What about in our area where you are required to have a ct enclosure. Would this be considered before the line side of the disconnect service? Would you need grounding bushings at every conduit coming in, and every nipple between the ct enclosure and the main disconnect?

Xcel Energy a while back required that we "cold sequence" the metering on all 3 phase business services. It was discussed and the put the thing on hold a while back. Seems like it confused alot of contractors. This would actually put the main service disconnect before the meter base or the ct enclosure.
 
dduffee,
Trevor, are you talking about where you come from the POCO transformer to the main disconnect? What about in our area where you are required to have a ct enclosure. Would this be considered before the line side of the disconnect service? Would you need grounding bushings at every conduit coming in, and every nipple between the ct enclosure and the main disconnect?
Click to expand...
At least one end of each of those raceways requires service type bonding.
Xcel Energy a while back required that we "cold sequence" the metering on all 3 phase business services. It was discussed and the put the thing on hold a while back. Seems like it confused alot of contractors. This would actually put the main service disconnect before the meter base or the ct enclosure.
Click to expand...
Unless that meter disconnect has overcurrent protective device in it, you will have to use service type bonding up to the actual service disconnect that contains the service OCPD.
Don
 
Status
Not open for further replies.
Top