I have a pole barn project where the owner is going to have half of the slab insulated and a hot water heating system installed in the slab. My question is this....from the definition of an equipotential plane in the NEC, it doesn't appear that it is necessary to have the concrete in direct contact with the earth so long as the grid in the concrete is bonded to the ground rod/case of the electrical system at the barn. It's not a case where the grid will be used as a ufer ground, which I realize has to be in contact with the earth.

Seems the half in contact/half not in contact would be ok as an equipotential plane so long as it is bonded adequately.

Your thoughts gentlemen?

If you drove rods at the 4 corners and bonded everything to the slab steel you would have a ground plane good enough for a radio station.