Attitude of code is that water pipe is not sufficient as the
primary or reliable earth ground connection. A separate
ground rod (or something equivalent) is required even if water
pipe earthing is available. Other incoming utilities will use
that ground rod as central earth ground; not water pipe.
Connection to water pipe is supplemental earthing to new
installations. Connection to one or multiple earth ground rod
(or whatever else you use for the earthing system), all at
same point, becomes single point earth ground. Everything
earths to multiple ground rods at same point. Even the
television aerial should make some connection to that single
point earth ground before entering a building even though the
aerial itself has a direct connection to a separate ground rod
- to fully optimize earthing for surge protection. These
exceed code requirements to make a superior protection
'system'.

That connection to water pipe is primarily to remove
currents from pipes - for human safety. Same safety reason is
why hot water pipes would also be grounded to panel ground.
If water pipe is also being used

Code requires a second ground rod if the first does not
measure less than 25 ohms. If second rod does not make less
than 25 ohms, then a third rod is not required - by code.
Code is not optimized for effective surge protection. If
earth is so non-conductive as to not supply less than 25 ohms,
then a more serious earthing system should be installed such
as halo ground, plate electrodes, or Ufer grounding. One rod
will make a minimally sufficient earthing connection in most
cases. Two rods will make every 'whole house' protector more
effective. The most important component in a surge
protection 'system' is its earth ground. Earthing and
distance of wire to that central earth ground will often be
the 'choke point' for system effectiveness. Additional money
spent on surge protection often is best spent on enhancing the
single point earth ground.

Code does not define how that earth resistance is to be
measured. Most locations will get less than 25 ohms with only
one ground rod. However, considering how important that
earthing system is also for transistor safety, then a second
rod is cheap insurance. Utility will install massive
grounding networks underneath a substation and still obtain
resistance on the order of 2 ohms. The first rod will lower
resistance. Every additional rod will provide less
improvement.


'nuther Bob wrote:
On Sat, 12 Jul 2003 03:22:50 GMT, "Mark or Sue"
wrote:
To summarize, if you have a metal water pipe that is in contact
with the earth for 10 feet or more, you MUST use it as your
primary grounding electrode.

WOuld "MUST" still apply if the proper attachment location to the
water pipe is 35 feet from the panel ? Or would the code then
prefer two grounding rods ?