250.166(B) DC GEC

[NorthwestPV]

In Article 250.166(B), it says the grounding electrode conductor shall not be smaller than the largest conductor supplied by the system.

I have a project with a 400 Amp service. Its GEC consists of a #6 Cu ran to two ground rods. I have 2 DC sets of #4 running to a combiner box. It is my understanding that the DC GEC must equal the sum of the DC conductors which would be a 1/0 Cu GEC. The NEC only requires a #6 to the ground rods no matter how large the service is. Do I really need to run a 1/0 to the existing ground rods? My feeling is I should only have to run a #6. Am I wrong in my thinking?

 

[jaggedben]

I don't think you're wrong (except that nowhere in the NEC does it suggest that the sum of DC conductors must be used, just the largest single conductor. So it is between #6 and #4, not #6 and 1/0).

You can use a #6. Note 250.166(C) contravenes (B) with respect to rods.

We just discussed pretty much the exact same thing yesterday in the PV forum. http://forums.mikeholt.com/showthread.php?t=147317

See also 690.47.

 

[NorthwestPV]

Thanks for the clarification. I was misinformed regarding adding the DC conductors together from a work colleague.