Greg G wrote:

On 19 Oct 2004 14:07:47 -0700, (coolneo) wrote:

Hi,

I'm reading up on some plumbing work I'm considering doing myself. I
have galvanized pipes throughout my house. I want to put in copper for
the new supply lines I want to install. I understand a Dielectric
union will allow me to "join" the copper with the galvanized iron and
protect from corrosion.

Great.

Continuing my reading I read someplace that since most older homes are
grounded to the plumbing the addition of a dielectic union will undo
the grounding.

OK, here's my inexpert take on it.

The dielectric union inserts an electrical insulator in the water
line. So if the dielectric union is between the grounding lug and the
city water supply, it would indeed disable the ground, as there would
not be an electrical connection to the earth, so to speak.

But in my house the grounding lug is attached to the cold water pipe
inches from where it first enters the house. I imagine that this is
typical. If yours is like that too I can't see how a dielectric union
further into the house plumbing would affect the grounding.

I have heard of larger buildings where people have "grounded" any
number of stupid things randomly to any pipe they could find, but I
hope that doesn't happen much in private homes.

I can even think of a few ways of testing for that, but I think you
should get more expert advice.

Greg Guarino

Actually, the grounding of switch boxes by virtue of the nearest
Cold water pipe was very common practice in much of the US
from the turn of the century till roughly 1965. After that,
Romex w/gnd was in widespread use.

There were exceptions, of course. Big cities mandated the use
of metallic raceway, other places used AC (BX) cable as a grounding
means. But millions upon millions of houses relied (still rely)
on the ground connection at the nearest Cold water pipe for
grounding of boxes for: bath switches, bath recepts, kitchen
counter recepts and switches, etc.

That's why plumbers have to be extra careful when disturbing
old runs of galv iron pipe.

Jim
much of the US from th