Concentric nuetrals and system ground

[Flyfishman]

We are doing a major 12.46kV distribution project where we proposed a single conductors with a shield tape cable (to be used to protect the actual cable)and separated ground conductor installed in PVC Conduit. The plant staff says that want concerntic neutral cable which they plan on using as a ground and delete the separated ground conductor. We have always been under the impression that you can't use the concentric neutral as a ground conductor.....Please give opinion

 

[chevyx92]

We are doing a major 12.46kV distribution project where we proposed a single conductors with a shield tape cable (to be used to protect the actual cable)and separated ground conductor installed in PVC Conduit. The plant staff says that want concerntic neutral cable which they plan on using as a ground and delete the separated ground conductor. We have always been under the impression that you can't use the concentric neutral as a ground conductor.....Please give opinion

From my understanding and experience the concentric neutral when at its terminations is grounded at the transformers, there isn't EGC. The concentric neutral acts as one. Don't quote me one this though. This won't be in the nec but rather the linemans handbook if I'm not mistaken.

 

[don_resqcapt19]

Are there any 7.2kV loads? If not there is no need for both grounded and grounding conductors. If there are 7.2kV loads, there still may not be a need for both conductors. Look at 250.32(B).

 

[beanland]

Utility vs NEC

Utility vs NEC

Utilities use concentric neutral cable all the time. The neutral is grounded at every accessible point. Industrial customers tend to use tape shield with separate ground because it is cheaper. Copperweld can also be used as a separate ground to save money.

2008 NEC 250.184 FPN states that multi-point grounding does not require a separate ground.