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Re: Presumed RF Interference

  • From: Ian Mason
  • Date: Tue Mar 07 08:13:01 2006 
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.