Matt wrote in message m...

I'm about to install a ceiling fan that needs earthing.
Unfortunately my existing ceiling rose is not supplied with an
earth. I assume this means I need to find a separate earth to
attach - is it best if I find a cold-water pipe and bond to that?

Dear me, no. The first point is that if your wiring is of such an age that
the lighting circuits have no earth, then you ought to be thinking in terms
of a complete re-wire before too long.

A temporary solution is to run a separate earth (properly called a 'circuit
protective conductor' or CPC) from your fan back to the main earth terminal
in your consumer unit or fuse-box (near the meter). A water pipe should not
be used as a CPC because (a) you can't rely on its continuity after plumbing
alterations (plastic pipes, Speedfit fittings, etc), and (b) in old wiring
there's probably no main bonding to the incoming water service in any case.

And what kind of cable / markings should I use for the earth
connection - just single strand green / yellow?

For a separate earth like this you will need 4mm^2 green & yellow
single-core earth wire. The cable type is called 6491X, but just ask for "4
mil earth". You'll find that it has seven strands, not one, BTW.

Strictly speaking, to comply with wiring regs your earth should follow the
same path back to the consumer unit as the other wires in the lighting
circuit. However that probably won't be a practical thing to do and
ignoring it is a much more minor transgression that not having an earth at
all.

HTH
--
Andy

In article ,
Andy Wade wrote:
For a separate earth like this you will need 4mm^2 green & yellow
single-core earth wire. The cable type is called 6491X, but just ask
for "4 mil earth". You'll find that it has seven strands, not one, BTW.

If this is now the 'legal' size, does it mean the 1mm earth built in to
most lighting TW&E is not satisfactory?

--
*Certain frogs can be frozen solid, then thawed, and survive *

Dave Plowman London SW 12
RIP Acorn

Hmm, that's interesting. My house is a 30's place, but the wiring
looks reasonably modern to me (circuit breakers not fuses, etc.) Just
how old would wiring be for you to expect lighting circuits to not be
earthed?

I can see the ceiling rose has been moved in the room in question, so
another possibility is that a new cable was installed for the move,
and earth omitted at that point. I'll investigate more closely.

Thanks..
Matt

Dear me, no. The first point is that if your wiring is of such an age that
the lighting circuits have no earth, then you ought to be thinking in terms
of a complete re-wire before too long.

Hmm, that's interesting. My house is a 30's place, but the wiring
looks reasonably modern to me (circuit breakers not fuses, etc.) Just
how old would wiring be for you to expect lighting circuits to not be
earthed?

It is very easy to replace a consumer unit and accessories. (I just replaced
my old fuse box with a modern consumer unit with RCBOs etc. in 3 hours). It
is very difficult, expensive, disruptive and time consuming to replace the
cabling. You will, therefore, find that consumer units and accessories do
not give a good indication of the age of the wiring as they are frequently
upgraded to keep up with developments. (i.e. old fuse box replaced with
MCBs, then an RCD or RCBOs are added at various times).

Basically, if the lighting circuit has no earth, it is probably pre-1970. If
it is made of rubber, instead of plastic, it is probably pre-1965. These are
not precise dates, however.

Christian.

Dave Plowman wrote in message ...

[4mm^2]

If this is now the 'legal' size, does it mean the 1mm earth built in
to most lighting TW&E is not satisfactory?

No, not at all. 4 mm^2 is the minimum size for an unprotected CPC which

- is not an integral part of a cable, or
- is not formed from metal conduit, trunking, etc., or
- is not contained in an enclosure formed by a wiring system.

[Reg. 543-01-01]

It's analogous to the 4mm^2 minimum size for supplementary bonding in
bathrooms: size is dictated by the need for mechanical, rather than
electrical, robustness.

--
Andy

I'm about to install a ceiling fan that needs earthing.

Cant you find a double insulated fan? No earth required then.

You could always run the ceiling fan from a fused connection unit to a
nearby ring main. I bet the socket circuits have earthing available.

Christian.