Strange Multi-way Light Switch Behavior

[jonnoh]

Hello all (on my first post, after being a long term lurker!).

We've got a little bit of complicated set of light switches in our hall and landing. The downstairs hall light is controlled by a single switch (switch D1) and a 2-gang switch (D2). The upstairs landing light is controlled by a single switch (U1) and also by the same 2-gang switch from downstairs (D2).

Today I took off the downstairs 2-gang (D2) to do a bit of wallpaper repair around it. I took photos of the switch and even labelled every wire with masking tape to make sure that everything went back the same way. After putting everything back the same (I've double, triple, quadruple etc. checked) the lights aren't working as expected, and confusingly the behaviour doesn't seem to be consistent.

The whole circuit works fine when D1 is turned on -- both the upstairs and downstairs lights can be controlled from the 2-gang and the upstairs light can be controlled from U1. However, when D1 is switched from on to off, any subsequent toggles of the switch on D2 that controls the downstairs light causes that light to briefly flash on and then go off (its like the light only works during the action of pressing the switch).

Strangely, this behaviour doesn't seem to happen all the time. I've taken the switch off the wall multiple times this evening to check everything is connected correctly. Sometimes when I screw the switch back on (2 times out of the 5 or 6 in total) everything just works fine, as its supposed to.

I wondered whether there was a loose connection that was shifting when the switch was pushed back into the wall box, which might explain the behaviour change when the switch is unscrewed. However, all seem very tightly attached.

I'm thinking about admitting defeat, turning off the lighting circuit and getting the electrician to fix my mess tomorrow (child and pregnant wife in the house, so feeling extra sensible right now!). However, I'd be really intrigued if anyone has any idea what might be going on!

 

[EFLImpudence]

Suspect faulty/worn switch - coincidences do happen.

Give the switch a thorough work-out. That is - switch on and off quickly multiple times.

OR

It is also possible that the actual copper wire inside the insulation has snapped (probably near a terminal but maybe not) and sometimes is touching and sometimes not.

 

[jonnoh]

Thanks very much for your reply.

I've tried the switch work out to with no luck. It makes sense that the broken wire could be the culprit, as I already snapped and had to reattach the earth jumper from the switch to the wall box earlier with all the ins and outs! If that's the case, I hope the snap is close to the terminal .

 

[EFLImpudence]

Feel if any of the wires is floppy at one point and bends too easily.

 

[securespark]

I have had this a few times. The conductor looks intact as the PVC insulation is continuous and often looks undamaged.

But the copper inside is broken.

 

[securespark]

When switch D1 is operated, does it affect either switch for the upstairs?

 

[jonnoh]

At the moment it doesn't. Everything with the upstairs light works as expected, no matter what position D1 is in.

However, the upstairs light did blow the first time I turned the power on after the switch was re-fitted, suggesting there's something wrong connected to that also (too many coincidences!).

 

[securespark]

What did it "blow"?