IANAEE (I'm not an electrical engineer etc...)

On Tue, 01 Feb 2005 12:23:39 +0000, Alan wrote:

Hello,

I wish to use some X10 transmitters within some [existing] light
switches (like these: http://www.homeautomation.eu.com/category/6),
however they require a neutral connection as well as live - and as
everyone knows this does not exist in a typical UK light switch.
Dropping a new neutral wire to existing switches would be impossible
except when each room is being decorated.

So, I'm looking at alternatives. One idea is to see about using earth as
neutral for this as it's just a reference point for the X10 signal. As
netural will be commoned to earth somewhere (incoming supply?
substation?) what reasons are there not to do this?

No - *don't* do this. The earth or CPC is designed for one main purpose
only, to carry off fault currents (and provide equipotential bonding with
respect to the ground). That's probably not the best (or even fully
correct) explanation, but it'll do for starters.

Doing anything else with the earth would be fundamentally bad practise.

Also, if these X10 devices do pass even a few mA then between them and you
install a few they might trip an RCD should you happen to have a 30mA one
covering the whole installation.

We're not talking about putting a load between live and earth, just
using earth as a reference point for a signal to be transmitted on the
live line from.

Understand. Really though - it is a fundamentally bad idea to use the earth.
Sorry I explain why any better.

Can I common up netural and earth in the CU?? I've yet to see what
voltage is between them but last time I looked a few years back it was
only a few volts.

Definately *don't* do this. Your electricity supplier will have a stated
way of providing an earth (or not in some cases). You must not interfere
with it. If, for example, they provide a seperate earth or CPC via the
supply cable, commoned back at the substation, then you can get some
potential difference between your neutral and earth. Connecting them in an
unauthorised way can give rise to large currents and generally annoys
electricity suppliers, apart from being dangerous.

My father saw a case once where a screw in a wall had gone through a cable
shorting the earth and neutral. Apparantly it got rather hot, to the point
of being a fire risk. It didn't blow any fuses because there were'nt any
in the neutral circuit.

Any other suggestions to get this working?

Well... Tricky one. I see you've found a funky X10 device I've not come
across before, if you mean Micromodule AW12.

Here's an idea:

Another way might be to use a different X10 setup with a remote X10
receiver controlling the light (install somewhere safe and convenient
where you can get the lighting supply and light pendant cables to it.

Then see if you can find a pure X10 single-address transmitter that looks
like a light switch, but isn't expecting the load to be wired in directly
to it. You might even be able to use some of the other X10 switch products
and just ignore the switched live output, and put the switch and the
receiver on the same address. Best to check with the manufacturer if in
any doubt - they're usually pretty helpful if you phone or email them.

*disclaimer*

I haven't done all the research into this myself, so these are just ideas,
may or may not be practical and and before Lurch jumps in and tells you
I've just suggested something dangerous (he means well and I'm fairly sure
I haven't!) it's upto to you to (as always with any online advice) to
consider your final solution and be satisfied that it's safe and correct.

HTH

Timbo