Ground Ring Conductor Bonding to Main Ground bar

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faresos

Senior Member
Hello everyone:

I have a 4/0 ground ring conductor that needs to be bonded with 4/0 to Main ground bar within the electrical room. The documents calls for 3/4"C PVC underground then transition to steel conduit once it turns up. The electrician has indicated they can't get ground bushing that allow connection of 4/0 copper wire to a 3/4" conduit. If we can go with PVC conduit then this will eliminate the bushing requirement but prefer to stick with steel for physical protection. other thought is to increase the conduit size to 2.5" to accomedate the 4/0 but I prefer not to do it. also, doe the bonding conductor needs to be 4/0 or can be reduced to 2/0? (per 250.66-C: the bonding conductor does not have to be larger than the ground ring). Any thoughts....
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
Hello everyone:

I have a 4/0 ground ring conductor that needs to be bonded with 4/0 to Main ground bar within the electrical room. The documents calls for 3/4"C PVC underground then transition to steel conduit once it turns up. The electrician has indicated they can't get ground bushing that allow connection of 4/0 copper wire to a 3/4" conduit. If we can go with PVC conduit then this will eliminate the bushing requirement but prefer to stick with steel for physical protection. other thought is to increase the conduit size to 2.5" to accomedate the 4/0 but I prefer not to do it. also, doe the bonding conductor needs to be 4/0 or can be reduced to 2/0? (per 250.66-C: the bonding conductor does not have to be larger than the ground ring). Any thoughts....

it seems to me that if you have to use steel you have to use an appropriately sized bushing.

your alternative would appear to be to use PVC and get a variance from the documents.

or, maybe you can put a ground clamp on the outside of the steel conduit and bond the 4/0 that way, although I am having a hard time seeing how that would work.
 

texie

Senior Member
Location
Fort Collins, Colorado
Occupation
Electrician, Contractor, Inspector
Hello everyone:

I have a 4/0 ground ring conductor that needs to be bonded with 4/0 to Main ground bar within the electrical room. The documents calls for 3/4"C PVC underground then transition to steel conduit once it turns up. The electrician has indicated they can't get ground bushing that allow connection of 4/0 copper wire to a 3/4" conduit. If we can go with PVC conduit then this will eliminate the bushing requirement but prefer to stick with steel for physical protection. other thought is to increase the conduit size to 2.5" to accomedate the 4/0 but I prefer not to do it. also, doe the bonding conductor needs to be 4/0 or can be reduced to 2/0? (per 250.66-C: the bonding conductor does not have to be larger than the ground ring). Any thoughts....

One way I have overcome this, especially if the raceway turns up very near the ground bus, is to use a ground clamp on the steel conduit and run a jumper (4/0 in your case) directly from the clamp to the ground bus.
 

cuba_pete

Senior Member
Location
Washington State
250.86 Other Conductor Enclosures and Raceways.
Except as permitted by 250.112(I), metal enclosures and raceways for other than service conductors shall be connected to the equipment grounding conductor.

...

Exception No. 2: Short sections of metal enclosures or raceways used to provide support or protection of cable assemblies from physical damage shall not be required to be connected to the equipment grounding conductor.

or depending on how you "turn up"...

Exception No. 3: A metal elbow shall not be required to be connected to the equipment grounding conductor where it is installed in a run of nonmetallic raceway and is isolated from possible contact by a minimum cover of 450 mm (18 in.) to any part of the elbow or is encased in not less than 50 mm (2 in.) of concrete.

Of course, the AHJ may look at you funny and make you do it anyway...



 
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don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
There is no easy way to change from PVC to rigid steel conduit underground and comply with 250.64(E). This is a case where both ends of the ferrous raceway must be bonded to the GEC and the bonding conductor is required to be the same size as the GEC.
 

faresos

Senior Member
Thank you for the replies. What I don't understand why we can't bond the conduit with #6 wire instead of 4/0 using ground clamp or it has to be the same size as the electrode conductor?
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
Thank you for the replies. What I don't understand why we can't bond the conduit with #6 wire instead of 4/0 using ground clamp or it has to be the same size as the electrode conductor?
The code requires a full size bond. Take a look a 250.64(E).
250.64(E) ...
(3) Size. The bonding jumper for a grounding electrode conductor raceway or cable armor shall be the same size as, or larger than, the enclosed grounding electrode conductor.
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
There are two exceptions which appear to apply directly to your situation. What is the problem applying those?
It appears to me that the conductor in question is a grounding electrode conductor and the code section that you cited does not apply. There are no exceptions to the required bonding of a ferrous raceway that contains an GEC.
 

cuba_pete

Senior Member
Location
Washington State
250.86 is for raceways for other than service conductors. Since the GEC is not a service conductor, I would apply it.

I understand that there is a specific section for the GEC (250.64), but I see that part stating ferrous raceways being continuous from the electrode to equipment not applying here since it is PVC...not required to be electrically continuous (and therefor bonded).

Then under that section, there is also: (4) Wiring Methods...If a raceway is used as protection for a grounding electrode conductor, the installation shall comply with the requirements of the appropriate raceway article.

So in addition, since the turn up is specifically for protection, here is where I think he could apply 250.86 exceptions 2 and 3.

If the assemblies part hangs you up, then you could only apply exception three which (from here) "looks" really close to what you are (or could be) doing.

The intent would be met in my view...
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
250.86 is for raceways for other than service conductors. Since the GEC is not a service conductor, I would apply it.

I understand that there is a specific section for the GEC (250.64), but I see that part stating ferrous raceways being continuous from the electrode to equipment not applying here since it is PVC...not required to be electrically continuous (and therefor bonded).

Then under that section, there is also: (4) Wiring Methods...If a raceway is used as protection for a grounding electrode conductor, the installation shall comply with the requirements of the appropriate raceway article.

So in addition, since the turn up is specifically for protection, here is where I think he could apply 250.86 exceptions 2 and 3.

If the assemblies part hangs you up, then you could only apply exception three which (from here) "looks" really close to what you are (or could be) doing.

The intent would be met in my view...
250.64(E) requires that a ferrous raceway that encloses a GEC must be electrically continuous....that requires that both ends of the ferrous raceway be bonded to the GEC. That would be difficult to accomplish if one end of the ferrous raceway is underground.
 

roger

Moderator
Staff member
Location
Fl
Occupation
Retired Electrician
Hello everyone:

I have a 4/0 ground ring conductor that needs to be bonded with 4/0 to Main ground bar within the electrical room. The documents calls for 3/4"C PVC underground then transition to steel conduit once it turns up.
The design is wrong, see Don's mention of 250.64(E)

The electrician has indicated they can't get ground bushing that allow connection of 4/0 copper wire to a 3/4" conduit.
If it weren't for 250.64(E) they could use a City Hub

Dottie-DOTHUB75L-37226.jpg


If we can go with PVC conduit then this will eliminate the bushing requirement but prefer to stick with steel for physical protection.
This is the best solution and if they are so concerned about physical protection tell them to use Schedule 80 above ground.

Roger
 
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