Help with wiring for dual dimmer switch

Hi guys,

Im a complete novice but hope someone can help. We have an extended kitchen out into an extension and have a dual dimmer switch: one for 6 GU10 lights in the original kitchen area and the other for a further 6 in the extension of the building. I didnt install them but were working fine.

The other day, i went to switch on the original kitchen set and there was a big spark from the dimmer switch box and the fusebox was tripped. Resetting the fusebox the extension switch worked but the faulty set still did not work.

Seeing nothing immediately wrong when opening the switch casing, we decided to buy a replacement to see if its a simple part fault. The inside of the switch looks like this:

https://goo.gl/images/M5EZYh

Heres the confusing part (at least for me), the instructions with the new switch unit are not very detailed and we have rewired as we thought it had been before:

Upper L1 feeding in

middle upper going to lower L2

Lower L1 feeding out

lower middle also fed (we were wondering if we should reverse this wire with the one feeding out of lower L1?)

It is clear a professional didnt install the switch originally - the wires going into the switch are all brown and the are part of a thicker bundle of cables with green/yellow included so assume earth is somehow handles outside the switch. The casing box set into the wall is notably not as deep as it perhaps should be and so the wiring is packed in (not ideal).

But now the extension lights switch works but the originsl kitchen 6 lights still arent working, suggesting (perhaps) that the original dimmy switch unit wasnt actually faulty. Anyone have some bright ideas? Perhaps if some could explain how such a switch should be wired it may also help.

CluelessSparkie said:

It is clear a professional didnt install the switch originally - the wires going into the switch are all brown and the are part of a thicker bundle of cables with green/yellow included so assume earth is somehow handles outside the switch. The casing box set into the wall is notably not as deep as it perhaps should be and so the wiring is packed in (not ideal).

Click to expand...

Which is a good sign IMHO .............. what do you think is wrong with this?

A possible cause is that there was a failure of the wiring at the lights causing a short circuit which was noted at the dimmer switch because of the high current through the switch, replacing the dimmer may well have restored power to the circuit but the original fault has probably blown clear by the short.

The arrangement of the wiring for the switch cannot be determined from a distance and would require testing to determine which wire does what.

The earth is normally not connected into the switch terminals but joined in the back box.

The dimmer itself should only be switching line conductors (coloured brown (or possibly red if older)).

Murdoch said:

Which is a good sign IMHO .............. what do you think is wrong with this?

Click to expand...

Well the wiring insulation was showing exposed wiring,some of the cables were set into the wall plaster and the left screw was set into plaster rather than the casing of the socket box... again I’m no expert but I imagine this is not the standard approach. Thanks for replying

Ardet R said:

A possible cause is that there was a failure of the wiring at the lights causing a short circuit which was noted at the dimmer switch because of the high current through the switch, replacing the dimmer may well have restored power to the circuit but the original fault has probably blown clear by the short.

The arrangement of the wiring for the switch cannot be determined from a distance and would require testing to determine which wire does what.

The earth is normally not connected into the switch terminals but joined in the back box.

The dimmer itself should only be switching line conductors (coloured brown (or possibly red if older)).

Click to expand...

Thank you for the reply. A lot of this is quite reassuring. Is it safe to try plugging in wires into different sockets then? Presumably if it’s not right it’ll either not work or trip the fuse? But you think it might be where the wiring connects to the light fixtures themselves right?

Replacing the switch does not seem to have done anything...

Thanks again!

I would not say it is safe to randomly plug wires into terminals.

It would be best to test to ensure you know which cables are doing what before connecting them.

If there is still a fault on the lighting circuit then this would need to be found and rectified before attempting to apply power back to the circuit.

Normally (or at least quite often) you would have a single live supply coming in and the switched lives coming out for each set of lights, however with two light switches and an extension and not knowing if there is two way switching it is not possible to say how it has been wired originally.

If all the cables to the switch are brown then there is no way by just looking at them to tell which is which.

CluelessSparkie said:

Well the wiring insulation was showing exposed wiring,some of the cables were set into the wall plaster and the left screw was set into plaster rather than the casing of the socket box... again I’m no expert but I imagine this is not the standard approach. Thanks for replying

Click to expand...

You didn’t say this in the op ....