NEC 250.30 - Separately Derived AC Systems

[ptrombley]

My situation is this- A 277/480 volt SES feeds a transformer (277/480 to 120/208) within the same building (for a typical tenant suite). The transformer constitutes a separately derived system (no grounded conductor pulled from the SES). The electrician wants to use the equipment grounding conductor from the SES to the transformer to also serve as the transformer's grounding electrode conductor. I'm use to seeing a ground rod driven at the transformer, or attachment of the GEC to building steel at the transformer. Is the electrician's method acceptable?

Thank you- Paul.

 

[benaround]

ptrombly,

Probably not, the only case he could be right is 250.30(7) exp.#2, all other

installs follow 250.30(7).

 

[ptrombley]

Thanks Frank- Is there a code section that prohibits a grounding electrode conductor in the same raceway with feeders? It seems to me there is, but I can't find it.

 

[raider1]

Is there a code section that prohibits a grounding electrode conductor in the same raceway with feeders? It seems to me there is, but I can't find it.

There isn't a code section that prohibits a GEC from being run in the same raceway with a feeder. But if the raceway is ferrous then you need to bond the GEC to each end of the raceway. (See 250.64(E))

Chris

 

[ptrombley]

Thanks Chris- For some reason I am uneasy about a lightning strike following the GEC back through the conduit which includes the feeders-- and back to the SES (since in this case the GEC would also be the EGC for the transformer. Does that concern you as well?

 

[raider1]

I have always routed my GEC's away from any other wiring the best I could. I would always run a separate non-ferrous raceway for the GEC as well.

Chris

 

[ptrombley]

Yes- That is how I feel also... but I guess it is not a code violation.

Thanks for your input.

 

[don_resqcapt19]

The transfomer in question is inside the same building as the service equipment. If you have lightning current on this GEC you have a lot more problems. Also an EGC on the primary is required and will provide the same path as the proposed GEC, the only difference will be the size of the conductor. I see no reason not to run the GEC with the primary feeder, assuming that there is no grounding electrodes available in the area of the SDS.
Don