electric light switch wiring

[lyndaann]

Hi,
I'm a relative newbie to diy, and have bought a dimmer light switch. I have a one gang system. However, on opening the old switch, I have found 3 wires, one blue, one red, and a yellow/green one, which is earthed. I know that yellow/green is the earth, so that's fine, and from research on the net, I think the red wire is live? I imagine the wiring in my house will be quite old, at least the 80's, I think.
The dimmer switch has two places to wire the red and blue to, but I need to know whether red or blue is the live one. I would really appreciate some info on this, if anyone knows.
When I replaced the ceiling light, the wiring was a different colour. From the old fitting, I worked out that the BLUE wire was live, and after wiring, this works fine. Another question is... does it matter which way this is wired? There was no earth wire, just a blue one, and a black one. SO CONFUSING! I'm worried now that if I assume the RED wire in the light switch is live, and the BLUE wire in the light fitting is live, that I will mess up the circuit.
I'd really appreciate any help, I know everyone says if you're not sure, to call an electrician, but money is a huge issue, this stupid flat is growing arms and legs lol...
Just need some reassurance really
Thanks,
Lynda

 

[VanSolo]

The red is the permanent live and the blue is the switched live ( should be marked with red tape. This is why you have the blue going to the live in the light fitting. In the dimmer red to common blue to L1.
Remember to isolate at the consumer unit before doing any electrical work and if in doubt, get in a professional.

 

[lyndaann]

Thanks so much for the quick reply,I've been looking at the switch all day lol

 

[ban-all-sheds]

The problem is, Lynda, that you've launched into doing things without knowing how it works and without getting the right tools. Learning how it works and doing it properly isn't beyond you, and it's what you really must do.

You've also got some strange wiring - the colours are odd combinations. At the time your flat was wired, twin and earth cable would have had red and black, and 3-core and earth would have been red, yellow & blue.

Are the cables you've found singles, or sheathed ones with more than one core?

When I replaced the ceiling light, the wiring was a different colour. From the old fitting, I worked out that the BLUE wire was live, and after wiring, this works fine.

That doesn't mean it is necessarily safe.

Another question is... does it matter which way this is wired?

It might do - depends what type of bulbs the fitting takes. If they are screw-in ones with the full sized base then the centre pin should be live and the outer thread should be neutral.

There was no earth wire,

Then you must not fit lights which require an earth, and until you have confirmed that the earths at other places, e.g. switches, actually work you must not fit metal switches etc..

SO CONFUSING!

http://www.diynot.com/wiki/electrics:lighting