Grounding Bushing

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Can someone either verify this or add to this question on when to use a grounding bushing. I know when you go through a concentric knockout, you need to put a bonding bushing on the pipe, but is it also true that a 150 volts to ground and up require one? And i:smile: s there any other condition that would require it?
 
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Conduits containing service conductors of any voltage are not allowed to rely on concentric knockouts to bond the conduit. Otherwise, if the voltage to ground is less than 250V, then a concentric knockout is allowed to bond the conduit.

Bear in mind also, most metallic 4" and 4 11/16" knockouts are listed for grounding over 250V to ground, which is permissible by 250.97's exception.​
 
I've found that it depends on the inspector. some want grounding bushings from the meter to the panel .others don't care at all
 
georgestolz said:


Conduits containing service conductors of any voltage are not allowed to rely on concentric knockouts to bond the conduit. Otherwise, if the voltage to ground is less than 250V, then a concentric knockout is allowed to bond the conduit.​




Just to clarify, service raceways are not permitted to be bonded by using standard locknut's regardless of whether or not there are concentric or eccentric KO's involved. They would require a bonding locknut, bonding bushing or bonding wedge.
 
Thank you for your post. But what about a 277 branch lighting circuit in a 3/4 conduit, would that need to have a ground bushing?
 
Thanks, Trevor. :cool:

pipebenderdon said:
But what about a 277 branch lighting circuit in a 3/4 conduit, would that need to have a ground bushing?
Not if it terminated in a four-square metallic outlet box listed for grounding over 250V, as all of the listed ones are.
 
georgestolz said:
Thanks, Trevor. :cool:


Not if it terminated in a four-square metallic outlet box listed for grounding over 250V, as all of the listed ones are.


I know that is what you meant.:cool:
 
Just a note for caution.
The bonding requirements for branch circuits changed somewhat a few cycles ago.
In the past before the manufacturers changed the design of the concentric and eccentric KOs, the bonding requirements were more restrictive. If you are working in an environment with older boxes, or reuse the older boxes you may have to provide a means for bonding. With the more modern boxes, that is not the case.

You can find some help in the UL White Book at (QCIT) METALLIC OUTLET BOXES and (BGUZ) BOXES, JUNCTION AND PULL ... under the subtittles "Concentric and Eccentric Knockouts".
 
tommy said:
How about the clamps that come with boxes for mc?I always use connectors when using 277 volt circuits

You can use the MC connectors inside the box at any voltage you might have in a device box.

It really does not mater as standard MC does not use the armor for grounding purposes anyway.
 
bond bushing requirements

bond bushing requirements

heres a good situation that i need opinions on.

we are renovating a school. several heat pumps are being installed above soft ceilings in hallways. Each hp are 3phase 480V/15A, and with several on one circuit. We are putting 100A fused discos next to each hp, and doing a feeder tap to hp. Since we are using 1 1/2" emt connected to the concentric KOs on discos, do you think we are required to use bond bushings?
Not knowing if GE's discos are listed for grounding above 250V I say yes, foreman on the job (rookie-first job) hasn't even heard of this requirement and thinks i am full of BS says not to worry about it.

So what do you think?
 
sheldon_ace said:
Since we are using 1 1/2" emt connected to the concentric KOs on discos, do you think we are required to use bond bushings?

Yes, I think you are required to use bonding bushings for that.

Unless the foreman can find info that the disconnects KOs listed for grounding.
 
iwire said:
Yes, I think you are required to use bonding bushings for that.

Unless the foreman can find info that the disconnects KOs listed for grounding.

iwire

since he wasn't even aware of the bonding requirement, which is in black and white in the NEC, i really don't think he would even have a clue about where to find UL listings. My philosophy would be to use the bond bushings just in case. This is a very large job, and i feel the cost of bond bushings and the labor to instal them would be insignificant, compared to the AHJ red tagging, and reworking them. i think there are 300 all together.

Also, where would i find UL listings for equipment. have tried searching before, but never seem to get anywhere. any help would be greatly appreciated.

thanks for the help

Gerry
 
sheldon_ace said:
My philosophy would be to use the bond bushings just in case.
Honest question, to everybody: Why not just avoid a ringed knockout, and drill your own hole?

This is a very large job, and i feel the cost of bond bushings and the labor to instal them would be insignificant, compared to the AHJ red tagging, and reworking them. i think there are 300 all together.
I have mixed feelings about this: on one hand, each disconnect was probably bid high enough that adding bonding bushings shouldn't sink the job.

On the other hand, paying for 300 bonding bushings at $10 a pop is leaving a lot of money on the table. I'm curious what most people do?

Also, where would i find UL listings for equipment. have tried searching before, but never seem to get anywhere. any help would be greatly appreciated.
In such a specific case, I would refer to the instructions that came with the disconnect, as opposed to searching the White Book for anything definitive.
 
Well, you could also just remove all the rings and use reducing washers instead of grounding bushings to save money. :grin:

Roger
 
roger said:
Well, you could also just remove all the rings and use reducing washers instead of grounding bushings to save money. :grin:

Roger

LMAO....:grin:

A very good point. :cool:


Its both true and kind of sad at the same time. :rolleyes:
 
Reply to Trevor's answer

Reply to Trevor's answer

regarding the metallic 4 square box, are you referring to the standard four square 2 1/8 deep or 1 1/2 inch deep box? I really have never heard it called a metallic box, is that what you are referring to?:)
 
to add to my question to Trevor;

to add to my question to Trevor;

one more thing I forgot to add on my prior question to you: If you are referring to the standard J box, how do I know it's listed for 250 volts, is it stamped on the box itself, or is it on the box they get shipped in? How do I know if it's listed for 250 volts? Where does it tell me that? Thanks Trevor!
 
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