ARW wrote:

On 27/04/2017 20:35, Roger Hayter wrote:
snip

My house was wired (presumably not by a professional) with 10mm^2
green/yellow wire parallelling all the T&E circuits from the CU
branching repeatedly with connection to all the pipework in every
room. Since it is all surface wiring (for structural reasons) in boxes
and trunking of various kinds I tend to strip out great reams of it
every time I redecorate or alter anything. As all circuits (except the
economy 7 one) are fast 30mA RCD protected it is hard to see what the
objective was, but it seems to imply a confusion between bonding and
circuit protection. Most of the rooms have no locally unearthed
metalwork in them apart from the central heating, which is all copper
anyway. For reasons which seem arbitrary, even earthed electrical
fittings (such as outside lights) seem often to have a parallel 10mm^2
earth connection back to the CU.



Perhaps someone read this and got confused.

http://electrical.theiet.org/wiring-...g.cfm?type=pdf

That's a thought, but seeing it was an ordinary house and done about
thirty years ago I suspect it was just a misunderstanding of
supplementary bonding. It is a PME installation.


--

Roger Hayter