In article , Bud-- wrote:
Doug Miller wrote:

In article , Bud--
wrote:


The NEC has for a very long time required that water service pipes be
used as a grounding electrode.


Note the word "a". Not "the".


So what? Metal water service pipes (10 ft or longer) are REQUIRED by
250.50 to be a part of the grounding electrode system. This basic
requirement has been in the code for a very long time.

"A part", yes -- but it is not permitted to be the *only* grounding electrode.

Ground rods are
not required to be installed.

Technically true, but misleading. You may use a ground rod, a ground plate, a
buried wire ring, or the metal framing of the building, as the *only*
grounding electrode. But not a water pipe.


The current code REQUIRES that water
service pipe with metal pipe underground length of 10 ft or more be
included as a grounding electrode.


And it flatly prohibits using it as the *only* grounding electrode.


So what? See reason.


Because this pipe may in the future
be replaced with plastic pipe, a supplemental electrode is required -
usually ground rod(s).


You have things backwards. The ground rod is the *primary* grounding
electrode, and the water piping is the supplemental electrode.


You have things backwards. With a water pipe a "supplemental" electrode
is required - 250.53-D-2. A "supplemental" ground rod is a strange name
for the "primary" grounding electrode.

The Code permits using a ground rod, alone, as the grounding electrode. It
prohibits using a water pipe, alone, as the grounding electrode. Quibbling
over which is "primary" and which is "supplemental" doesn't change those
facts.

Grounding rods are 'good' if their resistance to earth is 25 ohms or
less (or use 2 rods and it doesn't matter). Municipal water pipe earth
resistance is typically under 3 ohms.

Irrelevant. The Code does not permit a water pipe to be the only grounding
electrode.

Again:

"Bonding of piping systems... the basic concept is to ground any metal pipes
that would present a hazard if energized by an electrical circuit." [National
Electrical Code Handbook, Section 250-80]

I'm not sure why you're having so much trouble grasping this.

--
Regards,
Doug Miller (alphageek at milmac dot com)

It's time to throw all their damned tea in the harbor again.