600 Amp Feed And No Ground In RMC Conduit

[dwinchell]

I have discovered that a ground wire was not run in a 600 Amp Feed from Switchgear to an MCC. The run is 300-400 feet with RMC. What are my options?

I know there is some uncertainty on using conduit for a ground. From what I understand that is what the Engineer intended at the time. Can I use the conduit, run separate conduit just for the ground. Is there any other options.

Thanks

 

[infinity]

RMC is permitted to serve as the EGC. However, some have argued here on this forum that it can only be of a certain length before it loses it's effectiveness. You can not run the EGC in a separate conduit. Sounds like your best option is to leave it as is. Otherwise you would need to pull out the old conductors and pull in new ones with an EGC. This is contingent upon the conduit being large enough for the extra conductor.

 

[bob]

RMC makes a good EGC. Better than copper conductor when installed properly. Be sure that the connections are tight and you may want to call for double lock nuts.

However, some have argued here on this forum that it can only be of a certain length before it loses it's effectiveness.

Infinity
The question of lenght has been associated with the conductors called for in the EGC table not with conduit. The use of conductor effectiveness
is limited by long lengths. The NEC does not address this issue. It is a design problem not a code problem.

 

[infinity]

Infinity
The question of lenght has been associated with the conductors called for in the EGC table not with conduit. The use of conductor effectiveness
is limited by long lengths. The NEC does not address this issue. It is a design problem not a code problem.

There have been several discussions about the effectiveness of metal conduit as an EGC. Here is one from iwire:

I believe it has been stated that EMT is good for about 300' before it becomes an ineffective ground fault path.

Bob
_________________
Bob
Electrical Construction & Maintenance
Massachusetts

Also according to the IAEI Soares: Book on Grounding:

we have determined that to have a minimum current flow of 2000 amperes in a ground fault, we can install up to 235 feet of 3-inch conduit where a 400-ampere overcurrent device is used.

 

[tshea]

Also according to the IAEI Soares: Book on Grounding:

Quote:
we have determined that to have a minimum current flow of 2000 amperes in a ground fault, we can install up to 235 feet of 3-inch conduit where a 400-ampere overcurrent device is used.

RMC, IMC, EMT, (PVC :lol: )

You don't say what type of conduit.
I would vote in favor of threaded couplings being more capable than set screw or compression type couplings for carrying the fault current.

 

[infinity]

RMC, IMC, EMT, (PVC :lol: )

You don't say what type of conduit.
I would vote in favor of threaded couplings being more capable than set screw or compression type couplings for carrying the fault current.

Neither did the author. I would agree that in theory RMC made up wrench tight should be better than say EMT.

 

[PT]

Make sure the all your couplings and locknut & bussings are tightly installed. I read in a book that you can run a equipment ground conductor along the the RSC, bonding it as much as you can (to the conduit, box to box, metal enclosure to metal enclosure) giving you the continuity in grounding. Not sure if it is still allowed.

 

[don_resqcapt19]

PT,

I read in a book that you can run a equipment ground conductor along the the RSC, bonding it as much as you can (to the conduit, box to box, metal enclosure to metal enclosure) giving you the continuity in grounding. Not sure if it is still allowed.

It sure wasn't the NEC that you were reading. That is not permitted by the NEC.
Don

 

[PT]

thanks don.

 

[PT]

your right Don, NEC only allow EGC to be to bonded around the outside of a flexible metal conduit.