gfretwell,
personal experience, I had enough voltage to knock the snot out of me from the frame of everything to my terazzo floor. Cause, bad ground electrode. Remember you still have voltage drop on the neutral, even if everything is tight. You need to be sure it is the same potential as the slab
If you had that much voltage drop on the grounded conductor, then there was problem with the grounded conductor and a ground rod would not have solved the problem. If the grounding electrode was metal underground water piping system, then that grounding rod could have masked the symptoms of the problem, but would not have solved the problem. A ground rod would have masked the symptoms for only a few feet around the rod. If you had connected to the slab rebar, then that too would have masked the problem.
Don
