blueman wrote:
Jeff Wisnia writes:

Brad wrote:

Both pipes should be at the same electric potential (ground) since
they are both are buried.

Wrong, wrong...

Someone already mentioned the words "cathodic protection" with respect
to gas pipes.

What that means is that the gas company has connected a low voltage
source between a metal anode buried in the earth and the gas main and
the pipes leading off it to each user. The purpose is to make the
pipes slightly more electrically negative than ground so that they
don't get eaten away by galvanic corrosion.

The same sort of active protection is sometimes used at boat marinas
and on buried metal structures like guy wire anchors. The systems are
also known by the names "active cathodic protection" or "impressed
current protection".

There's a dielectric (insulated) coupling somewhere near the gas meter
to insulate the gas pipe in your house from the buried main and feeder
so that you don't "short out" that deliberately applied protection
voltage, because the gas pipe in your home probably gets electrically
grounded through some gas appliance it's connected to.

The use of plastic buried gas piping has eliiminated the need for
those kinds of corrosion protection systems on new work.



The grounding is done to help ensure the electrical panel has a true
ground.
In some cases the panel ground is wired to a long steel pole driven
into the earth. Just different ways to do the same thing.
Brad


According to your explanation, then I would think that the gas pipe
SHOULD be grounded. For you say that the in-house pipe is insulated
from the underground piping and hence NEITHER grounded nor "cathodic
protected".

Of course the pipe may end up being indirectly grounded through an
appliance ground, but that seems like all the more reason for
installing a solid, secure, permanent ground connection to the panel
ground. After all, what if the appliance is miswired and the appliance
ground is energized resulting in the pipe being energized (yet
insulated from earth ground), resulting in shock just like with a
water pipe...



I agree with you on that providing as you say, the grounding is done on
the house side of any insulated coupling.

I was responding the the "buried thus same potential" statement, and
should have made mention of the what you just did, that an "extra"
ground between the panel ground and the in-house gas piping can't hurt,
and may even be required by code.

Jeff

--
Jeffry Wisnia
(W1BSV + Brass Rat '57 EE)
"Rudeness is the weak man's imitation of strength."