Presumed RF Interference

Ian Mason nanog at ian.co.uk
Tue Mar 7 13:11:42 UTC 2006


On 6 Mar 2006, at 15:06, ww at styx.org 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 <matthew at sorbs.net> 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.






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