On 29/11/2011 20:41, Dave Liquorice wrote:
> On Tue, 29 Nov 2011 10:02:03 -0800 (PST), harry wrote:
>
> The electrical earth shouldn't be relying on buried metalic gas or
> water mains for its earth. That should be supplied by the DNO at the
> main earth terminal at the company fuse.
Or a proper earth electrode forming part of the electrical installation
can be used (TT system).
> True all incoming pipes should be bonded to the main earth terminal
> but that is to ensure that the pipework is all at the same potential.
This creates an equipotential zone indoors, but doesn't guarantee that
the electrical earth will be at the same potential as the soil outside.
Outside taps are best fed via plastic pipework or else a push-fit
plastic fitting should be inserted in the copper pipework near the tap.
This may not give complete electrical isolation, water being somewhat
conductive, but it will reduce the available shock current to a
non-lethal magnitude.
> Plumbers are not sparks and sometimes do not realise that their
> repair or modification with a bit of plastic(*) in a metal pipe
> compromises the electrical integrity of the installation. All bits of
> plastic joining bits of metal pipe should have bonds across them to
> maintain the electrical integrity.
There's no need for that at all, provided the requirements for main and
(where applicable) supplementary bonding are complied with, and that
boilers, immersion heaters, etc. etc., all have their own circuit
protective conductors.
--
Andy