On Fri, 22 Sep 2006 18:34:25 -0700, "Eigenvector"
wrote:

I'm not second-guessing my electrician, just gathering information for
later.

We agreed to install 2 ground rods, per code, and then tie a second ground

Guessing you live in a dry rocky soil area. Since code only requires
one ground rod if a sufficient low ground resistance.

to the water supply line, also code I am told. With that they are also
going to connect a ground between the hot and cold pipes at the water
heater.

My question, what does the ground at the water supply do that the 2 ground
rods don't?

1. Meet the requirements of code, it is the first you connect to if
the metal piping has 10 or more exposure to earth.

2. It bonds the pipe back to the panel, so if a hot wire comes in
contact it creates a strong ground fault to allow for breaker
tripping.

3. If the pipe is bonded to the panel, if you come in contact with
any neutral and a metal pipe, there will be a zero potential for
voltage and shock.

second question, as I intend on replacing all of my hot water lines with
PEX, obviously the ground at the water heater will no longer exist - am I
creating a dangerous condition or can I safely remove the metal hot water
pipes and replace with PEX - so that I no longer have any metalic hot water
pipes?

The water heater should be bonded ('grounded') via the electrial
supply and from the bonded ('grounded') gas piping. The bonding
jumper, from the hot to cold is to ensure 1. You maintain a bonding
('ground') back to the panel should your water heater becomes removed
for work. Also, just incase your water heater isn't good for low
impedance for ground fault current.

As for pex, you need to preplan all this. Talk to your building
inspectors as well as your electrical inspectors. I remember a
conversation with someone that pex wasn't allowed since it was believe
water applicances(garbage disposal, instant hot water heater), might
become engerized, and with no metal piping, a path for current would
be lost, and the situation could remain deadly.

Remember, do work per codes and inspector recommendations, not by
Newgroup posts. Be safe.

imho,

tom @ www.NoCostAds.com