bonding bushings

[twistedcivic90]

i've been having a debate with the general foreman on the jobsite.Please help,when exactly do u need to use a bonding bushing?? If your pulling a ground through the raceway and entering a encentric or conncentric KO, do u ever need to use one??

 

[macmikeman]

Re: bonding bushings

Above 250 volts to ground you do. Also anything coencentric at service if you are using metallic raceways.

 

[iwire]

Re: bonding bushings

Sorry Mike I can not agree with this.

Also anything concentric at service

IMO it is anything on the supply side of the service concentric or not.

twistedcivic90 This subject has many twists and turns as in general above 250 volt to ground you must bond around concentric unless the concentric are listed for grounding.

The sections of code you want to look at are 250.92 and 250.97, well actually you are better of looking at 250.90 through 250.106.

 

[augie47]

Re: bonding bushings

twist:
a quick note added to what bob said, most, if not all, of your standard boxes (4" sq, etc) have eccentric knockouts now and the boxes are listed for grounding so its not as big an issue as it once was.
in more direct answer to your question. , IMHO, yes. That EGC you pull does not necessarily ground the raceway itself. If you are dealing with >250v, and the raceway terminates in concentric k.os, not in an approved grounded on both ends, then, yes, you must address bonding the conduit by an approved means.

 

[twistedcivic90]

Re: bonding bushings

well how would i know if say, a Square D panel with concentric ko is rated for a good bond??

 

[don_resqcapt19]

Re: bonding bushings

twistedcivic90

well how would i know if say, a Square D panel with concentric ko is rated for a good bond??

That information would be in the instructions or marked on the panel labels. As far as I know, none of the concentric or other types of multiple size knock outs on panels are listed for bonding.
Don

 

[augie47]

Re: bonding bushings

twist,
I did a lil research on this, before I wondered if the question is applicable. >250v would be a panelboard, and I am not aware of any SqaurD pb's that have knockouts. <250 isn't applicable, unless its service, and service conduits can not depend on standard locknuts to bond anyway.

 

[macmikeman]

Re: bonding bushings

Hi Bob, your right again. I've been doing nothing but resi meter/mains with a hub for the grc mast for too many years in a row now. We don't need a bushing at all for those. I was forgetting. I used to do lots of commercial services and I would go ape with the bonding bushings, Those suckers were definitly bonded together.