Using existing building GES for building expansion


Senior Member
I have a project design where we are installing new LV/MV distribution inside of an empty space in an existing building (system expansion within same building). The new electrical system expansion includes the addition of a new 480V Swbd (fed from SE panel) a step-up transformer and a new MV MCC.

With this expansion as I described above the only thing that I would see that would require connection to a grounding electrode (GE) through a grounding electrode conductor (GEC) would be the transformer as a SDS per NEC 250.30.

Given that this new equipment is inside an existing building with an existing grounding electrode system (GES) would the practical approach here be to connect the required GEC for the new transformer back to the existing buildings GES?

I'm not quite sure what makes up the current buildings GES and weather it is ground rods, water pipes, steel columns, or a combination of several of these. Would a practical approach be to find what appears to be connected to the incoming SE panel in the electrical room and connect to it? I'm not sure how practical it may be in this case to find and connect to existing GES so looking for typical practical approaches for this case.