I'm really confused about the subject of using rebar in concrete as the grounding electrode. I guess this is based on field experience. In the early 1970s I was part of a crew that went around the country servicing GM Dealership signs. The pole sings were very large, 245 sq.ft. & very tall, 35 - 50 feet. The bases, foundations, were concrete with large anchor bolts and large amounts of rebar. Many of the signs we serviced had circuits shorted to the cabinet which resulted in the entire structure being energized. Most branch circuits had no grounding conductor but instead relied on the metal conduit. Over time the grounding path was lost and even though the 12 to 20 yards of concrete were in the ground, this wasn't enough to open the short circuit overcurrent device. A little boy was killed when he came into contact with one of these signs in the early 1970s in Fort Meade Florida. This resulted in the "GM Grounding Program" where a ground rod was driven next to each pole sign in a misguided effort to correct the problem. The point is this: with hundreds of feet of rebar, 20 yards of concrete, 4 ' anchor bolts and the steel structure, these signs were insulated by the concrete not grounded by it.