bond bushing

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Bonding bushings required when service conductors or 250 volt to ground conductors are installed in metallic raceways and concentrics are encounter at both ends of raceway system. Bonding is only required at one end.
 
Bea said:
Bonding bushings required when service conductors or 250 volt to ground conductors are installed in metallic raceways and concentrics are encounter at both ends of raceway system. Bonding is only required at one end.
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If I understand your post, this is not completely true. Using 110.3(B), we can get some guidance with the wording found in the UL White Book.
In Metallic Outlet Boxes (QCIT) and Boxes, Junction and Pull (BGUZ), we see writing that eliminates the requirement for additional bonding around concentric and eccentric knockouts.
"All boxes with concentric or eccentric knockouts have been investigated for bonding and are suitable for bonding without any additional bonding means around concentric(or eccentric) knockouts where used in circuits above or below 250 V, and may be marked as such."

I am not saying that bonding is not a good installation practice, I am just saying that the current boxes manufactured have been tested and show satisfactory performance results to permit relief of the need for additional bonding means.
If jobs are very competitive in regards to pricing, this could help give a contractor the advantage in pricing.
 
Pierre C Belarge said:
...If jobs are very competitive in regards to pricing, this could help give a contractor the advantage in pricing.
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Thank you for that. This is the sort of stuff our industry needs. Code education tied in with the business end of contracting.
 
Pierre C Belarge said:
If I understand your post, this is not completely true. Using 110.3(B), we can get some guidance with the wording found in the UL White Book.
In Metallic Outlet Boxes (QCIT) and Boxes, Junction and Pull (BGUZ), we see writing that eliminates the requirement for additional bonding around concentric and eccentric knockouts.
"All boxes with concentric or eccentric knockouts have been investigated for bonding and are suitable for bonding without any additional bonding means around concentric(or eccentric) knockouts where used in circuits above or below 250 V, and may be marked as such."

I am not saying that bonding is not a good installation practice, I am just saying that the current boxes manufactured have been tested and show satisfactory performance results to permit relief of the need for additional bonding means.
If jobs are very competitive in regards to pricing, this could help give a contractor the advantage in pricing.
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Is there a UL requirement that all boxes with concentric, eccentric or tangential KO's be tested for bonding over 250 volts? I have seen some boxes with a manufacturers' note stating that they are suitable for bonding and others that say no such thing. It is required as part of a listing? Can we assume that every box with these KO's is suitable for grounding? If questioned by an inspector who is responsible for proving that the boxes are suitable as required by the exception to 250.97.
 
I cannot answer the question whether allboxes are listed and investigated for the purpose. What I can say is, if the box is listed then it has been investigated and is suitable.

Also from UL:
"UL Mark
The Listing Mark on the product or the UL symbol on the product and the Listing Mark of Underwriters Laboratories Inc. on the smallest unit container in which the product is packaged is the only method provided by UL to identify products manufactured under its Listing and Follow-Up Service."


I would say that the UL symbol on these boxes would satisfy me as an inspector, that the box is suitable to be included in the "effective ground fault current path" required by Art 250.

In my opinion...remember this is my opinion.
Specs on certain jobs to include bonding come from "fear" (of litigation) and sometimes from an engineer having inadequate understanding/information about bonding. So they CYA and move on.
 
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Bea said:
Bonding is only required at one end.
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A GEC installed in a metallic raceway must be bonded to the raceway at both ends to negate "Choke Effect"

Along with the article sections provided by Chris, look at 250.92(A)(3)

Roger
 
The metallic outlet boxes is the only places in the UL White Book in which is says all boxes. All of the other places where it talks about concentric and eccentric knockouts says that the equpment will say whether it is suitable for bonding. The metallic boxes is the only piece of hardware in which they are all suitable.

Sorry, I just woke up, and I might not be explaining that clearly, but leaf through the white book and see for yourself.
 
I would also like to add that section 250.92 (B) does not allow "standard locknuts or bushings" to be used for bonding on the line side of a service, regardless of if there are no concentric or eccentric knockouts.

I hear alot of electricians that think that bonding bushings are only required on the line side of a service if the service raceways enter concentric or eccentric knockouts.

Chris
 
raider1 said:
I would also like to add that section 250.92 (B) does not allow "standard locknuts or bushings" to be used for bonding on the line side of a service, regardless of if there are no concentric or eccentric knockouts.

I hear alot of electricians that think that bonding bushings are only required on the line side of a service if the service raceways enter concentric or eccentric knockouts.

Chris
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I beleive all service raceways need bonding bushings? If I had a 400a disconnect and then a trough, with lets say (x) amount of meters and disconnects, and the meters were connected to the trough with offset nipples, then would the offset nipples need bonding bushings on both ends?
 
stickboy1375 said:
I beleive all service raceways need bonding bushings? If I had a 400a disconnect and then a trough, with lets say (x) amount of meters and disconnects, and the meters were connected to the trough with offset nipples, then would the offset nipples need bonding bushings on both ends?
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Service raceways only need bonding on one end.
 
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