Multiple Transformers, One GEC

[infinity]

If you have two transformers with #1/0 Cu secondary conductors and want to run one GEC how would you size it? Using 250.66 a single transformer with #1/0 Cu secondary conductors would require a #6 GEC. Running one GEC and tapping to each transformer would be sized according to what code article?

 

[don_resqcapt19]

I think the only provision for that is found in 250.30(A)(4) which requires a 3/0 grounding electrode conductor.

 

[Smart $]

Redundant...

 

[infinity]

I think the only provision for that is found in 250.30(A)(4) which requires a 3/0 grounding electrode conductor.

That's where I was leaning. There were a few suggestions, one being size the GEC based on the combined size of the two sets of secondary conductors but no code reference was evident.

 

[erickench]

It's called a common grounding electrode conductor as outlined in NEC 250.30 (A)(4). It's sized as a 3/0 copper or 250 MCM aluminum. The taps are sized in accordance with NEC 250.66.

 

[don_resqcapt19]

Rob,
Given that the 3/0 is over kill for your application, I would ask the AHJ for permission to use the provisions found in 250.64(D)(1). If that rule is good enough for services it should be good enough for an SDS.

 

[infinity]

Rob,
Given that the 3/0 is over kill for your application, I would ask the AHJ for permission to use the provisions found in 250.64(D)(1). If that rule is good enough for services it should be good enough for an SDS.

That was one argument but I suggested that it's not supported by the wording of the NEC. I just wanted to pull another GEC in an existing conduit (with the GEC for an existing transformer) but there are some compaints given that the run is 270' long.