Service Grounding

[bflaaen]

I know this may seem like a stupid question, but I seem to be having some problem finding the answer to this one.

We have a 3 phase, 4 wire, 480/277 volt system. The service entrance conductors from the transformer to the service entrance disconnect consist of 3 parallel sets of 3 - #350 phase conductors and 1 - #350 neutral conductor in PVC Sch. 80 conduit. I understand that at the service entrance disconnect, the neutral conductor must be bonded to the enclosure and a grounding electrode.

My questions is this: Is there supposed to be a ground conductor included with the service entrance cables from the transformer to the disconnect such that they consist of the following: 3 sets of 3 - #350 phase conductors, 1 - #350 neutral conductor, and 1 - #1/0 ground conductor.

 

[iwire]

Re: Service Grounding

No.

The neutral is bonded at the transformer and at the service disconnect.

If you where to run the 1/0 EGC between these two items it would actually become another neutral conductor.

 

[augie47]

Re: Service Grounding

For some unknown reason, I have seen engineered drawings that call for a GEC to the transformer pad...some of the more intelligent folks here can explain why, I'm sure, but I've never actually seen one installed.
And, no, its not a stupid question...even though mine may be a stupid answer..the closest the NEC comes to spelling it our, to me, is 250-24(A), 250-24(C)and 250-92
Since 250-24 (2) requires a grounded conductor connection to an electrode, as iwire points out, an additional 1/0 would be parallel and a violation.

 

[iwire]

Re: Service Grounding

I just go with the layman's version.

Have you ever seen or included an EGC between a POCO transformer and a single family home service disconnect?

The rules are the same for a 100 amp or 4000 amp service.

 

[charlie]

Re: Service Grounding

Besides that, we don't permit a grounding conductor in our transformer. We also prohibit metallic conduit that would require grounding bushings. These are our rules and not necessarily Code.