Goedjn wrote:
On Thu, 23 Feb 2006 13:00:16 GMT, (Doug Miller)
wrote:
In article , MC wrote:
FYI: May be no longer OK to ground to a water pipe in many locations
now. I prefer to only use ground rods anyway.
Correction: if a building has metal water pipes, it is a Code requirement (and
has been, for some time) that the metal water pipes be bonded to the
building's grounding electrode system. The Code prohibits using metal water
piping as the *only* grounding electrode.
Which in clear but imprecise terms, means that the the piping has
to be CONNECTED to the grounding system, but shouldn't be
used as PART of it. You connect the pipes to ground, but
you don't ground to the pipes.
Then what pray tell are you grounding to? The grounding impedance of
two driven rods is often over fifty ohms. The grounding impedance of
underground metal water pipes that are part of a community water system
is usually less than ten ohms. Changing what we say does not reverse
those figures. It is the underground metal water piping that provides
the low impedance connection to earth. The driven rods are strictly a
back up in case the piping is replaced with non conductive piping.
--
Tom Horne
--
"This alternating current stuff is just a fad. It is much too dangerous
for general use." Thomas Alva Edison