Grounding bushing?

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Dr Duke

Dr Duke

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North Dakota USA
Just got a correction notice on a building that we wired. The correction notice says that we need to install "grounding bushings" on a branch circuit. Basically out of a 480v panel, there is a branch circuit that runs to a closet where a disconnect is mounted. Out of the disconnect it feeds a plenum heater. The reason for the correction is cause we used concentric knockouts for the pipe. We also have our egc ran in the pipe. Am I missing a code section which requires me to have bonding bushings, on a 480v branch circuit, using concentric knockouts, while also having an egc installed with the circuit conductors?
I realize that if I didn't have an egc in the pipe while using the concentric, it would justify using bonding bushings. Any clarification would be appreciated.
 
The Code Section would be 250.97 which would be applicable as far as the raceway being bonded regardless of the presence of an actual conductor.
There are some exceptions referencing the listing of enclosures but they might well not apply in your situation.
 
In general disconnect switches with concentric or eccentric KO's are not listed as suitable for bonding.
 
Electricalartist said:
In some cases a bonding wedge or split collar bushing can save time when you've forgot to use a bonding bushing.
Click to expand...

Yes those split bushings can be a life saver when someone forgets about 250.97. Can a bonding wedge be used with concentric KO's?
 
infinity said:
In general disconnect switches with concentric or eccentric KO's are not listed as suitable for bonding.
Click to expand...

Do you know any examples of equipment with ring KO's that are listed for 277V or 277/480V bonding? I'd like to see how this is noted on a datasheet. I understand that these will be a lot more heavy duty than ordinary knockouts, and more difficult to remove.
 
Carultch said:
Do you know any examples of equipment with ring KO's that are listed for 277V or 277/480V bonding? I'd like to see how this is noted on a datasheet. I understand that these will be a lot more heavy duty than ordinary knockouts, and more difficult to remove.
Click to expand...
Some 4S boxes are, you can tell has the KOs are hard to remove. I have a picture in my grounding class of an approved box but not sure if I have any on the shelf
 
Carultch said:
Do you know any examples of equipment with ring KO's that are listed for 277V or 277/480V bonding? I'd like to see how this is noted on a datasheet. I understand that these will be a lot more heavy duty than ordinary knockouts, and more difficult to remove.
Click to expand...

There was a thread a while ago where someone posted a reference to the KO's in disconnect switches not be tested as suitable for grounding over 250 volts. Most 1900 and 4 11/16 boxes that I've seen are so listed.
 
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