Drive two ground rods at least six feet apart. (In some cases, where the ground conductivity is really good, one will suffice.)
The grounding electrode system of a house starts with this:
1. The panel ground terminal strip (ground bus)
2. A grounding electrode which may be either the main cold water pipe provided it is metal and is buried outside for at least 10 feet, or two ground rods,
3. A #6* copper wire running non-stop between the above two items.
If the main water feed entering the house has been replaced by plastic, you need to have ground rods for an alternate grounding electrode.
If you started out with ground rods, the metal parts of the plumbing system in the basement must be bonded to the grounding electrode system using #6* copper wires as needed. Using clamps, put a #6 jumper wire across the water meter inlet and outlet and across the water heater (cold) inlet and (hot) outlet.
If you have additional ground rods, say for cable TV, these must be tied (bonded) to the above. A ground rod in a detached garage or other building is bonded using the ground wire in the power feed over from the main house. Exception: No bonding needed where the wiring to the main house was grandfathered to not need a ground wire back to the house.
If A is bonded to B and B is bonded to C then A is bonded to C. So if a metal water pipe going upstairs is jumpered using a wire past a plastic section of pipe and clamped to the wire in part 3 above then that metal pipe is bonded to the panel ground.
Metal plumbing upstairs electrically isolated because of plastic pipe sections should be bonded using jumper wires more or less following the pipes down to the basement. These wires should be at least the size of the largest branch circuit wiring passing near the respective pipes (typically #12). Clamp the other end to a pipe that is bonded or to somewhere on the grounding electrode system described above.
Gas piping must be bonded to the grounding electrode system also. But if you have a gas appliance with electrical components, then the ground wire in the cable or conduit feeding that appliance and going back to the panel is a good enough bonding.
* The connection to the entering water pipe (if metal) must be within 5 feet of where it enters and before the water meter. For services greater than 100 amps those bonding wire(s) between the entering water pipe and the panel need to be #4 copper.
Last edited by ajaynejr; 01-28-2011 at 06:05 AM.