Doug Miller wrote:
In article . net, wrote:
Doug Miller wrote:
In article , Bud--
wrote:
Your fact is not consistent with what you said:
�The electrical system has its own, *separate* grounding electrode.
Metal water piping is bonded to the electrical system grounding
electrodes to ensure that the metal water piping cannot become live,
*not* to provide a ground for the electrical system.�
I do not see how "*not* to provide a ground for the electrical system"
can be read other than the water pipe is not to be a grounding electrode
and the system grounding is provided by the system's "own, *separate*
grounding electrode."
It's real simple: the water pipe is bonded to the other grounding electrodes,
not to provide a ground for the electrical system -- that's what the *other*
electrodes are there for, remember? -- but to ensure that the metal water
piping is always at the same potential as the electrical system's ground and
therefore cannot become live no matter *what* might go wrong electrically.
I'm sorry that you're having such a hard time grasping this... but you really
need to spend a little more time educating yourself before you post again.
"250.50 Grounding Electrode System.
If available on the premises at each building or structure served, each
item in 250.52(A)(1) through (A)(6) shall be bonded together to form the
grounding electrode system.
250.52 Grounding Electrodes.
(A) Electrodes Permitted for Grounding.
(1) Metal Underground Water Pipe. A metal underground water pipe in
direct contact with the earth for 3.0 m (10 ft) or more (including any
metal well casing effectively bonded to the pipe) and electrically
continuous (or made electrically continuous by bonding around insulating
joints or insulating pipe) to the points of connection of the grounding
electrode conductor and the bonding conductors. Interior metal water
piping located more than 1.52 m (5 ft) from the point of entrance to the
building shall not be used as a part of the grounding electrode system
or as a conductor to interconnect electrodes that are part of the
grounding electrode system." Copyright 2002 National Fire Protection
Association
I hope you're not contending that metal underground water piping is permitted
to be the *sole* grounding electrode...
Now who is it that needs to educate themselves?
Geez, *another* one with reading comprehension problems. I have never disputed
that metal underground water piping is required to be part of the grounding
electrode system.
The whole argument is over *why*.
Is your position on why so as to keep it at the same potential as the
other electrodes? Yes or no no dodging.
My position on why is that it is the best electrode available on
premises served by large underground metallic water systems. In a
building with no internal metallic plumbing supplied by a utility that
requires copper laterals; many do; why do we still need to connect the
Grounding Electrode Conductor to that piping. How is it to become
energized in the absence of interior metallic piping? Why does the code
require that the portion of the GEC that is the connection to the
underground metal water piping be sized according to the table rather
than limited in size like the one to the Concrete Encased Electrode,
Ground Ring, Driven Rods, and so forth. It is because it is a superior
electrode to any of those others. How many Grounding Electrode Systems
have you measured for impedance to ground? How many have you installed?
I cannot answer such questions my self because I lost track decades
ago. In areas served by metallic public water systems I've never found
an electrode with a lower impedance to ground than the metallic water
service lateral from the metal water mains. That includes the ground
rings and genuine Ufers installed at radio stations and the deep driven
rod arrays installed at telegraphic fire alarm receiving stations.
--
Tom Horne
Well we aren't no thin blue heroes and yet we aren't no blackguards to.
We're just working men and woman most remarkable like you.