Strange problem with 2 way light circuit

[ilikewatchingtv]

Hi,
I would appreciate your ideas about the following problem. Last week I had an electrician round to rewire most of the upstairs lighting loop in my house. Everything looked good and appeared to work well afterwards. My hallway/landing is on a 2 way circuit with a light and switch at the top and bottom of the stairs. yesterday I removed the surface mount downstairs hall lighting switch so that I could chase in the cable and a back box. I rewired the switch as before, with the only change being the addition of earth sheath on the bare earth wire in the enclosure. Today, the lights weren't working... after some messing about I discovered that the lights only work if the upstairs landing switch is in the on position. If this switch is in the off position neither light can be switched on from the bottom of the stairs. I'm sure that my work yesterday can't have caused this, but then I hadn't noticed the problem until today. Does anyone have any thoughts about what might be causing this? Many thanks in advance for any help!

 

[securespark]

You have reconnected the switch wrongly, or a wire is loose or snapped off.

Check wiring to L1 & L2 terminals.

 

[ilikewatchingtv]

I'm sure I haven't reconnected the switch incorrectly, - I drew a diagram of the connections before I started and everything is wired the same way now. None of the wires joining the downstairs switch appear to be loose, or snapped near to the switch. I take it if a wire was snapped somewhere in the circuit it would have to be within the 3 core & earth between the top and bottom switch, presumably if anything in the T&E which goes from the pendant in the upstairs ceiling to the upstairs switch was amiss, then nothing would work?

 

[securespark]

It depends.

You say you have a T&E cable and a 3 core at one switch. Presumably then, at the other switch is the 3 core.

Tell you what, then. Make safe. Disconnect the 3 core altogether from both switches, noting how it was connected.

Reconnect the twin & earth to C and L1.

Reinstate power. Does the light work one-way?

If so, switch off again. Using the E as reference and a continuity meter, short the e to a colour & test at the other end between those two conductors. You should have continuity.

If you have full continuity & the switch works one-way, reinstate the wiring fully.

Does it still fail to light??

 

[ilikewatchingtv]

Great idea! - have just dug out my multimeter and will test continuity as you suggest tomorrow, - thanks for the help

 

[securespark]

Just take care with the voltage - make sure with your multimeter (?) that you are off before disconnecting...

 

[ilikewatchingtv]

Ok, have followed the advice given so far, after removing the 3 core & earth the circuit works fine 1 way. I have continuity tested the 3 core and earth and it seems fine. However, after reassembly the problem persists that both switches need to be on for the lights to work. Any further ideas?

 

[luminaire]

It should look something like this:-
At the switch with the 3-core:
yellow on C (or could be red)
Red on L1 (unless red on C), blue on L2.

At the other switch:
The T&E should be on L1 & L2 (assuming you do have a 2-way switch)
The 3-core should be something like - R to L1 (together with say R from T&E)
B to L2 (with say Black from T&E)
and say Y to C (assuming yellow is on C on other switch)

Then at the ceiling rose - the R from T&E will be connected in with the permanent lives. The black from T&E will be the switched live.

(The 3-core just goes from one switch to the other.)

 

[ilikewatchingtv]

Ok, solved it now! Securespark was right, it was a wire snapped inside the sheath about an inch from the switch terminal. The problem was that the gap between the wires only opened up when the faceplate was screwed in, so I never spotted it when I tested continuity with the faceplate off. Luckily there was enough spare cable to make up the difference. Thanks for everyones help