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Re: Presumed RF Interference

  • From: Andrew C Burnette
  • Date: Wed Mar 08 15:30:39 2006 

Ian Mason wrote:

On 6 Mar 2006, at 15:06, [email protected] wrote:


On Mon, Mar 06, 2006 at 09:49:39AM -0500, Steven M. Bellovin wrote:


On Mon, 06 Mar 2006 21:17:17 +1100
Matthew Sullivan <[email protected]> wrote:
(In the
UK where I served my apprenticeship, we were required to provide earth
bonding to the copper plumbing system, additional bonding at every
exposed fitting - this caused a few issues when plumbers first starting
using PVC pipes)...
The US National Electrical Code (which has no national force of law;
it's a model code voluntarily adopted by many jurisdictions) now bars
grounding to pipes except within (as I recall) six feet of where the
pipe enters the building, for precisely that reason.

The use in modern times of teflon tape at joints in copper
piping makes them unuseable for earth grounds even near the entry
point to the building. A long (e.g. 2-3 meters) copper stake must be
driven for a proper earth ground, or else a large copper mesh mat if
the ground is rocky -- unless you are certain that the copper piping
that you want to use extends a significant distance underground and
unbroken.
The purpose here is not to use the piping *as* a ground, but to ensure that the piping *is* at ground potential. Otherwise, if an electrical failure causes the pipe to reach a dangerous potential then so does the water in it, then so do the hands you're washing in that water. Thus if there's an electrical discontinuity in the piping it is even more important to earth bond any conductive piping/taps etc. that are on the non-earth side of that discontinuity. The same applies too to gas piping except here the principal risk is static, sparks and the subsequent explosion.



I think it is also important to note that NEC 250.52(B) prohibits gas piping as a grounding electrode(1990 or so). The gas pipe ceased as a grounding electrode due to the dielectric fitting at the meter. The gas company did not want a bond around the meter because it defeated the isolation fitting.

The presence of gas is not relevant, IIRC.

In the old days, it was a big no no (at least according to the hourly wage fellows who actually do the work) to hook the gas line "as" ground other than any incidental grounding which ocurs in a gas furnace as an example.

Good place for resources is http://www.mikeholt.com in the forums. Decent community of knowledgeable folk there.

Good luck, and "no" do not use your body/fingers/arms/etc to connect various pieces of equipment to see if a voltage exists:-) That's best left to close friends who stand near electric fences.

I had problems in the mid 1990's in an older home where the galvanized water supply pipe was the primary ground. Over time, corrosion of the pipe reduced conductivity, and lightening storms toasted a few expensive items (e.g. ISDN gear, sun workstation, etc) before finally driving a few grounding bars into the soil in the basement.

Cheers,
andy