Bert Coules wrote:

I agree that on the face of it it seems an odd requirement, but it
just seems simpler not to argue, really. I would be interested in an
idiot's-guide explanation as to why it's necessary, if anyone would be
kind enough...

We've been through this multiple times - as a groups.google.com look in
uk.d-i-y will show. No-one's yet been arrassed to put the Conclusion in
the FAQ.

There is NO requirement to earth a kitchen sink. The IEE On-Site guide
goes so far as to use almost exactly those words - i.e. it doesn't just
not mention sinks under 'things wot must be earthed'; after that list,
it gives another list of 'things wot you might think must be earthed but
for which there ain't no such requirement'. And kitchen sinks is on that
second list.

But there's a widely-read trade 'Bible', Whitfield's Guide-to-the-Regs,
wot makes a big song and dance about what a good idea it is to earth a
kitchen sink. It doesn't put the other side of the case - that providing
a well-earthed sink to lean against (especially if you're in
bare-midriff mode: middle-aged male uk.d-i-y'er on the rare hot day of
summer, or fashion-conscious female young in (actual or virtual) years)
you increase the harm from a touch-something-live fault.

Bottom line - it's arguable both ways, and with copper piping you're
unlikely not to have it earthed thru the taps anyway. If you want to
either bond it explicitly to the pipework, or earth it to a nearby
socket, go ahead; but you won't find any authoritative cable size to
use, because the only authoritative source doesn't require it to be done.

Stefek