I wish to use some X10 transmitters within some [existing] light switches (like these:
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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? 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. 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.
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.
Understand. Really though - it is a fundamentally bad idea to use the earth. Sorry I explain why any better.
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.
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.
On an aside, the reason there's a few volts there is due to the the impedance of a fairly hefty neutral core in the street supply cable between the consumers and the substation.
It might be a few volts, but if you provide a second path for the neutral current to return to the transformer (via the ground) then proportion of that current[1] will be diverted via your earth and your common joint. That's going to get hot. Also, if your neutral suffers a fault further up the line you're in danger of everything in your house rising to some undesireable voltage.
There are types of supply earth where something like this is done but the suppliers know what they are doing more than you or me ;-/ And they design it work in that way.
[1] Not just your current, but any other neutral current in your area will back feed to your earth bond)
.........And this is why I posted here before trying anything! It's easier to ask for advise and workarounds than find out the hard way when it all goes wrong! Hmmmm. Getting neutral to the switches is going to be a PITA.
How about using the 4th core of the three core & earth to the existing two-way switches - and letting X10 take care of the 2 way switching needs? Then the cores will become live, switched live, neutral and earth...?
2 of the switches I wish to control are part of a 2 way switching arrangement so this could be reasonably easy to do.
Yes, this one's good: this is a pretty common usage of 3+E when wiring fans with a run-on timer, for example, and is much cleaner than dribbling return currents to earth or to some other circuit's neutral.
I probably should clarify that you could, with the above method, just rewire the existing swich cable from up above the ceiling to be across the L+N of the lighting circuit which allows you to leave the existing cable in place.
The X10 switch gets its feed and no need for the load supply wire as that's handled by the remote X10 receiver module.
Stefek answered this already, it's a perfectly good way to do it.
Let us know how you get on - I'm thinking of maybe using X10 for some garden lighting (rather than running lots of SWA back to the house, I can just run one lighting supply circuit and use the DIN rail X10 modules in waterproof housings near each set of lights). Could be a good setup for the pond too...
X10 will do this easily - I have a similar setup but have the modules in the garage, all fed via a SWA to the house. Works great. Current project is trying to get X10 control of existing lights with the minimum of disruption to each room to keep SWMBO happy!
I quite fancy doing something like this, along with perhaps some method to control garden sprinklers, but am concerened about reliability. If controlled from say, a ring main, the signals would have to go back to the CU, through an RCD, meter tails, a switchfuse, 30m armoured cable, and then another RCD before reaching the module. How does this compare to your setup? Have you had any reliability issues?
Why would the signal need to go over meter tails? Is there a seperate meter to each building? If so you may be fed from different phases...
My arrangement from X10 computer controller goes: (computer in loft, mains supplied as spur from upstairs ring main) Ring > CU > MCB > busbar > MCB > 30m (ish) SWA cable > garage CU main switch > busbar > MCB > radial circuit in garage > X10 module. Signals travel fine in both directions, if I use an X10 transmitter in the garage, the computer recieves them fine also.
We have the house CU, and two switchfuses (garage / summerhouse) all fed from a henley block, hence the need for the signals to go via a short length of meter tail. All comes from the same supply though.
OK sounds fairly similar, with the exception of the two RCDs. Has anyone had any luck sending X10 through an RCD? Any thoughts on typical inductance for these, as they'll need to pass 120kHz.
Yes, I've gone over 2 RCD's also between the split load CU RCD side, and into the kitchen fed from it's on MRCD(?) on the non-CD side of the CU. Works fine also.
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