Gec

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domnic

Senior Member
Occupation
Electrical Contractor
When installing a grounding elecrode conductor in EMT conduit when do i need a grounding bushing at the end of the EMT?
 

buzzbar

Senior Member
Location
Tacoma, WA
Occupation
Electrical Contractor
Are you talking about the GEC or the EGC?
EMT only has to be bonded at one end if you are only needing to ground the conduit. If you are using the conduit as a ground, or bond, you'll need to bond it at both ends.
That being said, you only need to use a grounded 'bushing' if there are concentrics on the enclosure. If there are no concentrics, then a grounded locknut will suffice.

Make sense?
 

Cow

Senior Member
Location
Eastern Oregon
Are you talking about the GEC or the EGC?
EMT only has to be bonded at one end if you are only needing to ground the conduit. If you are using the conduit as a ground, or bond, you'll need to bond it at both ends.
That being said, you only need to use a grounded 'bushing' if there are concentrics on the enclosure. If there are no concentrics, then a grounded locknut will suffice.

Make sense?
I think you're missing the fact this EMT is a sleeve for the grounding electrode conductor. Take a look at 250.64(E). Bonding needs to happens at BOTH ends of the raceway.
 

kwired

Electron manager
Location
NE Nebraska
The answer is in 250.64(E).

A GEC in a metal raceway must be bonded to both ends of the metal raceway, and the metal raceway must be electrically continuous.

Any time you have a single conductor in a metal raceway you will have magnetic fields around the contained conductor that will have effects (all of which I can not remember at this moment) on the raceway containing that conductor.

This is part of the reason why 300.3(B) requires all conductors of the same circuit to be installed within the same raceway. The only exception to that involves non metallic raceways.

With services, feeders, branch circuits you have other conductors with current flowing in opposite direction and if all circuit conductors are in the same raceway the net magnetic effects on the enclosing raceway is zero.
 

roger

Moderator
Staff member
Location
Fl
Occupation
Electrician
Are you talking about the GEC or the EGC?
EMT only has to be bonded at one end if you are only needing to ground the conduit. If you are using the conduit as a ground, or bond, you'll need to bond it at both ends.
That being said, you only need to use a grounded 'bushing' if there are concentrics on the enclosure. If there are no concentrics, then a grounded locknut will suffice.

Make sense?
See the illustration below and the text in red.



Roger
 

kwired

Electron manager
Location
NE Nebraska
See the illustration below and the text in red.



Roger
The comment at the bottom of that photo needs some changes. The pictured raceway is electrically continuous without the additional bonding. It needs to indicate why bonding of both ends is necessary even though it is already electrically continuous.
 

1793

Senior Member
The comment at the bottom of that photo needs some changes. The pictured raceway is electrically continuous without the additional bonding. It needs to indicate why bonding of both ends is necessary even though it is already electrically continuous.
I beg to differ with the Bold statement above. The raceway, EMT, in the illustration is NOT continuous, it does not attach to the Ground Rod or Ground clamp.
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Electrical Contractor
I beg to differ with the Bold statement above. The raceway, EMT, in the illustration is NOT continuous, it does not attach to the Ground Rod or Ground clamp.

It says it shall be made electrically continuous. This is done thru the bonding jumper. No?
 

buzzbar

Senior Member
Location
Tacoma, WA
Occupation
Electrical Contractor
I think you're missing the fact this EMT is a sleeve for the grounding electrode conductor. Take a look at 250.64(E). Bonding needs to happens at BOTH ends of the raceway.
You're correct, I missed that fact. So, why would anyone use EMT for this purpose then?
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Electrical Contractor
You're correct, I missed that fact. So, why would anyone use EMT for this purpose then?
In commercial building you may not be allowed to use PVC so emt is often run to protect the gec. I am thinking to building steel or water pipes not ground rods. Specs may not allow PVC to the rod either.
 

Cow

Senior Member
Location
Eastern Oregon
You're correct, I missed that fact. So, why would anyone use EMT for this purpose then?
One example, I'm wiring a large warehouse right now with lots of EMT going out of the electrical rooms 15-20' vertically to get up into the trusses. There's no way I'm sticking one piece of pvc in an otherwise all EMT rack just to avoid a couple bonding bushings...:roll:

Besides asthetics, the support requirements suck for pvc. I don't want to have to strap every 3 feet or so.
 

1793

Senior Member
The comment at the bottom of that photo needs some changes. The pictured raceway is electrically continuous without the additional bonding. It needs to indicate why bonding of both ends is necessary even though it is already electrically continuous.
I beg to differ with the Bold statement above. The raceway, EMT, in the illustration is NOT continuous, it does not attach to the Ground Rod or Ground clamp.
It says it shall be made electrically continuous. This is done thru the bonding jumper. No?
Yes I agree that the bonding jumper makes it so, I was referring to the statement above in bold italics underlined.
 

kwired

Electron manager
Location
NE Nebraska
I beg to differ with the Bold statement above. The raceway, EMT, in the illustration is NOT continuous, it does not attach to the Ground Rod or Ground clamp.
Or to the single cabinet hole it enters through to the buss bar.
If you place the leads of an ohmmeter on opposite ends of a metallic raceway you are saying you will not have continiuity? The raceway is a conductor of electricity and is electrically continuous. The reasons for bonding each end have nothing to do with continuity of the raceway and everything to do with reducing heating from magnetic effects induced on the raceway.
 

1793

Senior Member
If you place the leads of an ohmmeter on opposite ends of a metallic raceway you are saying you will not have continiuity? The raceway is a conductor of electricity and is electrically continuous. The reasons for bonding each end have nothing to do with continuity of the raceway and everything to do with reducing heating from magnetic effects induced on the raceway.
All I'm saying is that the metal raceway in the illustration is a sleeve and not a raceway because it is not attached to the ground rod or clamp itself there for it needs to be bonded on both ends to reduce the Choke Effect.
 

kwired

Electron manager
Location
NE Nebraska
All I'm saying is that the metal raceway in the illustration is a sleeve and not a raceway because it is not attached to the ground rod or clamp itself there for it needs to be bonded on both ends to reduce the Choke Effect.
That is true - but that is not what I was after when I said "The comment at the bottom of that photo needs some changes."

The comment at the bottom of the photo says "Ferrous enclosures containing the grounding electrode conductor must be made electrically continuous"

That statement needs worded differently. The ferrous enclosure (which I incorrectly referred to as a raceway) is electrically continuous without the bonding jumpers - it is already made out of conductive material and is similar consistancy throughout.

Making the enclosure electrically continuous is not the reason for installing the bonding jumper to each end. Reducing "choke effect" (thank you for finding some words for me that I was not coming up with) is why the bonding jumper is installed.

Even Mike Holt can make mistakes. His installation requirements in the photo are correct but there is incorrect reasoning of what is actually happening there.
 
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