one way switch - 2 live wires, and only 1 neutral?

I am trying to replace one metal dimmer switch for another as the switch in the kitchen that had just stopped working - all other lights working fine on the circuit.

It\\\'s more a less a swap of identical dimmer switches i.e. a switch with L1, L2 and Common with a green/yellow earth for another of the same.

Coming into the back were two red wires, which I am 99% sure were both going into L1, with the blue into common, and earthed. By the time I took the screw out holding the red wires in, the exposed copper of one wasn\\\'t long enough to work with in the new switch - the \\\"end\\\" was still inside the contacts

What I don\\\'t understand is the kitchen should only be a 1-way switch as far as I can tell, but why is there one blue, but 2 reds? So I have tried putting the wires back as they were - 2 reds in L1, blue in common, earth connect but this trips the fuse?

Strange colours indeed. You are connecting the earth to the backbox, yes?

The colours could be explained by this being a conduit installation. Do they go into a pipe in the wall?

The only thing i can suggest is that the blue was terminated by itself in a bit of terminal strip, and is a neutral (this would explain fuse blowing when you turn it on, but its unusual to have a single neutral at a switch), and the Reds go across the switch - one in COM, one in L1.

Be careful with the dimmer - you could wreck it. Only way to know which wire does what is to find the other end of them and check.

Firstly sorry about the \\\'s - I was posted from here
//www.diynot.com/pages/el/el029.php
which did that

It seems like the red with the extremely short piece of copper (which probably wouldn't have touched the copper on the other red) and the thickness of the insulation, that that red is probably not meant to be there

It would then be red in L1 and blue in common as it was when I took it out

If that fails, I'll get someone in cos I've just done a straight swap of one two way switch for another

PS Sorry yes I did connect earth. In fact first time I tried a plain plastic on off switch which wasn't earthed, and got the same effect, which is why I then tried the earthed one

crafty1289 said:

Strange colours indeed. You are connecting the earth to the backbox, yes?

The colours could be explained by this being a conduit installation. Do they go into a pipe in the wall?

The only thing i can suggest is that the blue was terminated by itself in a bit of terminal strip, and is a neutral (this would explain fuse blowing when you turn it on, but its unusual to have a single neutral at a switch), and the Reds go across the switch - one in COM, one in L1.

Be careful with the dimmer - you could wreck it. Only way to know which wire does what is to find the other end of them and check.

Click to expand...

When you say "ususual to have a single neutral", it's the fact there are 2 reds and one blue that's unusual in what as far as we can see is just a way circuit

I've checked inside the old switch, and the single blue wire was in L2 - end of wire definately exposed and nothing inside the contacts to terminate itself. The 2 reds were definately in COM as I just tried to transfer it over

I changed a 2 way switch for a 2 way dimmer no problem not so long ago - I did have a bit of space trouble fitting the 2 the wires in the same hole, which is why on this occasion I made the effort to just swap them straight away

\\\'s are a known problem, catches most of us once (PS you can edit )

first post L1 - both reds, L2 - nothing, Common - blue
subsequent post L1 - one red, L2 - nothing, Common - blue (other red terminated)
last post L1 - nothing, L2 - blue, Common - both reds

Hmm I think the best thing would be to take nothing for granted, check out where the other end of each wire terminates, and then follow the instructions for the new switch from there.

If it wasn't for the fact that it is a dimmer then which wire you connected to common and which to one of the Ls wouldn't matter as much, but dimmers may well need the supply to a particular terminal. IMO put whatever you believe the old connection pattern was to one side, work out what cable's doing what, and connect the new switch from scratch.

Sorry for the confusion over the posts.

This is definately correct now....
...2 reds were going into common
... the blue was going into L2
I am just replacing a dimmer for a bogo standard on off switch in the kitchen, so technically it shouldn't matter what side of the switch the load is on, should it?

It's probably unlikely one of the reds was terminated - as I found the end of the copper wire inside the terminal contacts

Interestingly, I was in the same position as MarkH with his "lights just stopped working...." thread before I changed the downstairs switch