2 way switch puzzle

[onephatdiver]

Hi Guys, please help!
I have x2 4 gang MK switches in my kitchen, 3 switches controlling 3 12V lighting circuits. (The 4th control a landing light and outside light, which we can ignore).
My problem is this: One of the lighting circuits will not switch correctly. The 2nd switch, connected to the 3c+e operates the light, the 1st switch, with the 2c+e & 3c+e does not. If the 2nd switch is turned on and the lights lit, then the 1st switch will turn the lights off, but the 2nd switch will not turn the lights back on again. I have substituted the switch to eliminate any fault there, but as the junction box is wired correctly and there are two other switches wired identically and working fine right next to the problematic one, I am at a loss.
Any ideas? Cheers.

 

[ban-all-sheds]

Have you looked at the reference section for drawings of how the switches should be wired?

I take it they've always been like this for you, and that they didn't start doing it recently?

Have a go at comparing what you've got with those diagrams, it might be less work for you than trying to describe here exactly which conductors of which cables are connected to which terminals...

 

[onephatdiver]

No need to check switch wiring, it's simple and as I say there are two other switches right next door working fine. The only un-common denominator is the type of transformer used to drop the voltage. The two circuits which are working fine have Toroidal transformers, with one input and an output for each lamp (3 lamps on each circuit), the dodgy circuit has an electronic transformer switched at a junction box. It's one of the twin wire systems with 5 20W bulbs strung along it.
Yes, the switching has always been working incorrectly. The transformer blowing and needing replacement has prompted me to try to get to the bottom of the problem.....
I hope this sheds a little more light on the problem, I appreciate you attention.
Cheers

 

[ban-all-sheds]

Have you checked the continuity of the cores in the 3C+E cable connecting the L1s and L2s of the offending switch pair?

 

[onephatdiver]

Hello again,

Bingo, no continuity in the wire connecting L2. It's good to know whats wrong, but the cable cannot easily be replaced.

So the next question (a long shot) is: Can two way switching be 'fudged' using only the red and yellow wires of the 3C+E cable?

Cheers
Nick

 

[ban-all-sheds]

Yes, but then you'd have to take the switched live from the COM of the other switch, and kendor will berate you about eddy currents.

He may or may not be right , but how easy would it be to take a switch cable from the other switch to the light?

PS - I wonder what caused the discontinuity? Do you know where the cable runs? Can you see anything that might have been fixed to the wall and bvggered it?

 

[onephatdiver]

Well there has been some pretty heavy duty building work carried out and a break could have quite feasibly occurred during that, but thinking about it the cable may have been broken during installation as the 2 way switching has never worked.

Now it's a long time since A level physics, whats the deal with eddy currents?

Also you'll have to speak to me like I'm a five yr old, I take the switched live from the other switch, and do what with it?
L1 black/red & yellow, L2 red & red, to L1 yellow L2 red?

 

[ban-all-sheds]