The Electrical Contractor Network

ECN Electrical Forum
Discussion Forums for Electricians, Inspectors and Related Professionals

Books, Tools and Test Equipment for Electrical and Construction Trades

   
Topic Options
Rate This Topic
#174381 - 02/03/08 11:59 AM Proper use of ground bushings?
SP4RX Offline
Member
Registered: 10/01/07
Posts: 56
Loc: 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
Top
Work Gear for Electricians and the Trades
#174385 - 02/03/08 12:52 PM Re: Proper use of ground bushings? [Re: SP4RX]
sparkyinak Offline
Member
Registered: 07/08/07
Posts: 1310
Loc: 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
Top
#174392 - 02/03/08 04:47 PM Re: Proper use of ground bushings? [Re: sparkyinak]
gfretwell Offline


Member
Registered: 07/20/04
Posts: 9066
Loc: 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
Top
#174393 - 02/03/08 05:11 PM Re: Proper use of ground bushings? [Re: gfretwell]
Sixer Offline
Member
Registered: 08/08/05
Posts: 264
Loc: 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?"
Top
#174423 - 02/04/08 01:14 PM Re: Proper use of ground bushings? [Re: Sixer]
GA76JW Offline
Member
Registered: 03/20/04
Posts: 195
Loc: 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

Top

Featured:

2017 NEC and Related
2017 NEC
Now Available!

Shout Box

Recent Posts
Forum Styles
by Admin
Today at 02:22 PM
License exam
by TRUE POWER
Yesterday at 09:16 PM
Looking for older post
by sparkyinak
Yesterday at 12:27 AM
Members: Non-Members: Did you know?
by Admin
01/22/17 02:34 PM
Safety at heights?
by HotLine1
01/21/17 08:51 PM

Who's Online
1 registered (Admin), 102 Guests and 11 Spiders online.
Key: Admin, Global Mod, Mod
New in the Gallery:
Desk-mounted "power-board"
Top Posters
gfretwell 9066
Trumpy 8560
pauluk 7693
HotLine1 6833
sparky 5545
Member Spotlight
Member Since: 10/19/00
Posts: 2724

ECN Electrical Forums - sponsored by Electrical Contractor Network - Electrical and Code Related Discussion for Electrical Contractors, Electricians, Inspectors, Instructors, Engineers and other related Professionals