w_tom is slipping. I keep throwing random refs to surge protectors
into Usenet and private-forum posts, and he never comes in to reply.
Correct me if I am wrong, but there was a time when the NEC
allowed one to ground equipment to a nearby water pipe. Of
course, there was also a time (look at the 1899 code, which is
posted online somewhere) when they allowed one to use a gas
pipe as a grounding electrode. The time for either of those is
Back when men were men and jackets were braided, one could
safely assume that all pipes were metal. Metal pipes full of water
from the ground to the might well provide a nice low-impedance
path to ground. But we can't assume that now. My own house
has all metal pipes. Were I to open up a 2nd floor wall, and install
a ground clamp on a cold water pipe, and test the ground, it
would probably be excellent. But then the wall is closed, the
Down the road, somebody replaces sections of the copper cold
water pipes with plastic. Now I have a ground connected to a
pipe, connected to nothing, and unless somebody tests the
ground before and after plumbing, nobody is going to know
about it. One day there is a direct short to ground. Fixtures
have been replumbed with plastic supply connectors, except
one old sink with separate hot and cold faucets. The cold
faucet is now hot. The hot faucet is still bonded to ground
at the water heater. Somebody turns one on, and reaches
for the other...
In any case, a falsely advertised ground is bad enough; a
ground that goes to unbonded metal is worse, and that's what
grounding to a water pipe can get you. Sometimes I see
washers or dryers that had been grounded to a nearby pipe.
This isn't as bad in an unfinished basement; you can see all
the pipe, but it's also the situation where putting in a run of
grounded cable and a new receptacle is very easy.
Besides, if you're going to pull a single conductor into a
space, you might as well pull in a cable, as somebody up
there pointed out.