DIY Doctor UK DIY Forums

Good evening,
I replaced a standard 2 gang plastic switch a few months ago in my lounge with a chrome plate type dimmer. I have a single pendant in the middle of the room and 2 wall lights. The wall lights are operated by one of the switches and the pendant is operated by the other. The house is 1935 but has been rewired in the last 15-20 years.

Firstly, I have two cables in the box - the first one is twin and earth, the second one is just twin with no earth. The twin and earth has red tape around the black wire so I have assumed that is the switch wire, the twin cable has a red wire and black wire with some brown tape around the end because it wasnt connected in the old switch.

Everything I have read so far has told me to connect both of the black wires into the relevant connecters for each switch (L1). The red wires on both cables go into the relevant connecters for each switch (com) and then the earth from the twin and earth cable is connected to the back box with another piece of earth connecting the front plate to the earth on the back box. That all sounds straightforward enough to me but why wasnt the black wire with brown tape connected previously?

Anyway, the switch was working absolutely fine until today when I replaced a single gang one way switch on the wall in the room on the opposite side of the lounge I mentioned above. The siwtches in each room are back to back effectively athough the walls are very thick so I doubt they touch.

When I turned the power back on I heard a short buzzing noise from the two gang switch in the lounge and when I tried switching teh lights on it wouldnt work. I took it apart and one of the circuit boards on one of the switches had blown. So, I replaced the switch with another one of the same type and the same thing happened although i did notice that it was working fine until I screwed the plate back to the wall.

Could this be as simple as an earthing fault? Everything looks tightly connected and no wires are getting trapped. Or could it be related to the replacing of the switch on the wall behind in a dfferent room???

Any help would be appreciated.

Everything was working fine until you replaced second switch, did you take a note of the configuration of the cables within this switch prior to removal or have you made assumptions.
The thing is it did work before this, is this also chrome did you connect the earths as you stated earth terminal on switch plate to back box before screwing plate on. you said it work before you screwed it back!
what cables have you in this switch?
Is the lounge a two way switch are the lights operated by another switch?
KB

I'm pretty sure I put the cables back in the same order on the the switch in the other room but as its a one way single gang switch I didnt think it made a huge difference? The cables in the switch in the other room are same as the lounge. A twin and a twin/earth. The red wire from the twin and the red wire from the twin/earth are connected into the com conductor, the black switch wire from the twin/earth is in the L1 conductor. The earth from the twin/earth is connected to the back box which is in turn connected to the front plate. The black wire from the twin is just taped up and not used.

As far as I can see, all of the earths are connected and tight, I'm happy with that.

The switch in the lounge is one way only but operates wall and pendant lights.

You said these switches are back to back do you know if the cables are fed through the wall between the boxes. So say a hole was directly between the back boxes and cables are running between the two switches. Also check the insulation of the cables for bare conductor in the boxes and around gromet holes.
KB

If it works fine until you fix the switch back to the wall, you must be fuoling a cable with the swich fixing screws