On Mon, 19 Jan 2004 23:29:40 -0000, "Owain"
wrote:

"Nick" wrote
| Thanks for this info, but I am still a little unsure of how to
| proceed. Am I right that a normal light switch (with one COM
| and one L1 terminal) will not be usable?
| If I need another type of switch (a normal switch with four
| terminals is what the other bathroom has) can you tell me
| what this is called, and which wires go where?

Basic concept of the answer is correct, pretty much as my post further
down! However,

I don't think you've got a ceiling light switch - which would be single-pole
two-way (COM, L1 and L2 terminals)

I think you've got a DOUBLE-POLE ceiling switch of the type used for
electric showers, one pole is doing the light, and the other pole is doing
the *shared* fan. Is it a square plate and decidedly chunky in style?

Not neccessarilly, you can get quite unobtrusively small cieling
mounted 20A pull switches.
they're usually rated at 30 or 45A for showers rather than 6A for
lightswitches.

IE wired something like this (SWa = switch a, which has two poles)


LIVE -------------- SWa Pole 1----------- LIGHT -- Neutral
|
|-- SWa Pole 2-----
|
|
-- SHARED -- Neutral
-- FAN
|
|
|-- SWb Pole 2-----
|
LIVE -------------- SWb Pole 1 ---------- LIGHT -- Neutral

Pretty good, You should do more!

This would correspond to your

- Red to one terminal
- Black to one terminal
- Second red shared to two terminals by way of a link

The "second red shared to two" would be the live linking to SWa Pole1 and
SWa Pole 2 above.

Using this, when either switch is on the shared fan gets electricity, as
does the switch's own light, but the electricity can't run back through the
other switch to the other light.

If this is the case then I think it contravenes the Regs (a) by the colour
coding - it sounds as though the Black to one terminal is the live to either
the light or fan (b) by not running line and neutral of a circuit in
parallel close together.

This doesn't contravene the regs in any instance. It is perfectly
acceptable to use black as a switch wire as long as it is marked with
red sleeving or similar at all connections. Live and neutral can run
wherever they like, as long as they are connected properly and routed
in accordance with the regs.

It's possible the 'normal' switch with four terminals the other bathroom has
is an INTERMEDIATE light switch, but I don't see how it could be wired the
same way because AFAIK Intermediate switches aren't available in pull-cord.

As I said, 20A DP clg switches look like normal one's, same size and
external appearance.

If the 'normal' switch the other bathroom has is also a bit chunkier (and
maybe a red rocker) than a light switch it's almost certainly a DP switch.

God help you is all I can say, because my head is starting to hurt with the
strangeness of it all :-)

Obviously you're not an electrician then!! I've recently finished
wiring 16 fans, 6 speed controllers, 8 automatic changover units all
with varios methods of switching. I could explain how I did that if
you want!?


SJW
A.C.S. Ltd.