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Proper use of ground bushings? #174381
02/03/08 03:59 PM
02/03/08 03:59 PM
S
SP4RX  Offline OP
Member
Joined: Oct 2007
Posts: 56
Edmonton, Alberta, Canada...eh
Hi all, I have a question for you about when and why a person would use a ground bushing...it has never really been explained to me.

One guy I worked with wanted one at either end of a run of Teck cable, but he couldn't explain the reasoning for this. The other day I was talking with another co-worker about this and he says it isn't necessary.

Back when I was doing residential work it was necessary to use a ground bushing on the connector inside the panel to properly bond the service entrance conduit. I guess the connector doesn't provide adequate bonding in this situation?

The code wording doesn't make sense to me so I figured you might be able to explain it a lil' better.


Thanks a bunch

Work Gear for Electricians and the Trades
Re: Proper use of ground bushings? [Re: SP4RX] #174385
02/03/08 04:52 PM
02/03/08 04:52 PM
S
sparkyinak  Offline
Member
Joined: Jul 2007
Posts: 1,334
Alaska
Bonding bushing should be used anytime a metal conduit enters any type of enclosure when the conductivity can not be ensured across where the conduit and enclosure meet. One example is a cocked conduit or a conduit is not square to the enclosure. this will prevent the locknut(s) from mating squarely to the box. Another example is the concentric / eccentric knockouts. Although they are usually rated for carry fault current, some times they limited on the rating or the concentric / eccentric sometimes get banged around during installation. When in doubt, throw on a bonding bushing.


"Live Awesome!" - Kevin Carosa
Re: Proper use of ground bushings? [Re: sparkyinak] #174392
02/03/08 08:47 PM
02/03/08 08:47 PM
G
gfretwell  Offline

Member
Joined: Jul 2004
Posts: 9,242
Estero,Fl,usa
Service conduits require bond bushings because you simply can't count on the lock nuts to handle fault current of service conductors. There was a picture floating around IAEI a while ago of a 4" conduit that had burned out the whole area of the enclosure where the lock nuts were.


Greg Fretwell
Re: Proper use of ground bushings? [Re: gfretwell] #174393
02/03/08 09:11 PM
02/03/08 09:11 PM
S
Sixer  Offline
Member
Joined: Aug 2005
Posts: 265
Canada
Sparkyinak and gfretwell nailed it on the head.
I'll elaborate a bit further:
The reasoning for requiring a bonding bushing on a service entrance is that locknuts need to bite through paint or rust in order to contact bare metal and give good continuity to ground. Since we're talking about service entrances there's a high fault current available. Should a conductor short against the connector or conduit you want this to have good ground continuity.

Another example of requiring a bonding bushing or ground wedge would be when using PVC boxes and having teck cable or metal conduit run between them. The conduit or the armour of the cable would not be grounded by just using locknuts against a PVC box.


Sixer

"Will it be cheaper if I drill the holes for you?"
Re: Proper use of ground bushings? [Re: Sixer] #174423
02/04/08 05:14 PM
02/04/08 05:14 PM
G
GA76JW  Offline
Member
Joined: Mar 2004
Posts: 193
Suwanee, GA USA
We also use bonding bushings when we have a run of flex in between two points. Most usually with transformer feeds on the primary and secondary sides.


"If common sense was common, everyone would have it"-not sure, someone here


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