Changing a light switch....

[RedSnapper]

....should be simple, right?

Old bakelite light switch has broken so new one required. It's one of three that try to independently control the downstairs and upstairs hall/landing lights.

Historically the upstairs and downstairs switches have worked fine inasmuch as we could switch the lights on/off from either switch. The middle switch on a half landing by the bathroom has a mind of its own - it will switch the lights on and off but if it is switched on then the other two switches won't work at all.

I eventually found a reasonable facsimile of the switch to be replace and ordered it in 2 way style. I wired it in the same way as the old one, at least as far as I could work it out. However, now, the upstairs and downstairs switches both need to be 'on' for the lights to come on and the landing switch will only work if both the others are off

I've looked at the wired and got even more confused:

Upstairs - 2 red, 2 blue (intermediate switch?)
Halfway - 1 red, 1 blue, 1 black (three terminal switch)
Downstairs - 1 red, 1 blue, 1 yellow (and an earth not connected). (three terminal switch marked, Common, 1 way, 2 way and a 4th marked loop that's not connected to anything).


Before I call a sparky out, any clues?

[ReformedCharacter]

Not sure from your comment whether you have replaced the upstairs or downstairs switch, you may find this helpful:

http://www.lightwiring.co.uk/tag/2-way-switch-wiring-diagram/

The simplest explanation from your description is that you have transposed connection 1 and 2 as shown in the first image.

RC

[csearle]

Upstairs - 2 red, 2 blue (intermediate switch?)
Halfway - 1 red, 1 blue, 1 black (three terminal switch)
Downstairs - 1 red, 1 blue, 1 yellow (and an earth not connected). (three terminal switch marked, Common, 1 way, 2 way and a 4th marked loop that's not connected to anything).

Before I call a sparky out, any clues?

Are you prepared to do a bit of investigation?

Because the colours at the three switches don't match (at least if I've understood you correctly) then there must be hidden junctions. Whether the arrangement can be made to work properly will depend upon what is connected to what.

If I were the sparky investigating I'd do the following (during daylight). I'd make sure there were no kids around and warn any other adults to avoid touching wires. Having turned all lighting circuits off I'd take all switches off and separate out the various wires. I'd turn each lighting circuit in turn back on and use one of these (or similar) voltage detectors to establish which of all the wires is the permanent feed from the fuseboard. I'd then turn the circuit(s) off again.

Next I'd try and establish which of the other wires are actually connected to each other. I'd do this by either using a trailing lead and a continuity tester or by connecting together pairs and using said continuity tester.

I'm looking for two switch locations to be connected together by three separate connexions. Actually I'm looking for that twice, between two pairs of switch locations. One switch location hopefully is common to both. This is the location of the intermediate switch. The others are the locations of the normal 2-way switches.

If you are up for this then I (or someone else) can help further. If not then go ahead with the sparky. (If you are not too far from Tunbridge Wells in Kent or Bude in Cornwall then I can help you!

Chris
PS The two-red, two-blue location does indeed sound like the location of the intermediate switch but over the years I've come to learn that the acid test is what is connected to what rather than what colour any particular wire is. (C.f. comments in programming, they can say what they want but what happens is what is coded!)

PPS It could be that the intermediate switch has not been furnished with the connexion that is doesn't use. In which case what you'd be looking for would be two coonexions to each of the other switches (the third being connected elsewhere and not presented at the switch. Hope that makes sense.

[Hardgrafter]

This you tube series explains light wiring very clearly, in my opinion, including the issues caused by miswiring.
https://www.youtube.com/watch?v=dnpV781c6Sw

[jfgw]

If you have three wires and three terminals, there are only six ways of connecting them. Since L1 and L2 do much the same thing, you only have to try three different ways to find one that works (and you have tried one of those already).

Connect one of the wires to COMMON. Connect the other two to L1 and L2 (either way around). See if it works. If it doesn't, try a different wire in COMMON (and the other two in L1 and L2). If it still doesn't work, try the remaining wire in COMMON. If the original fault was due to the switch that you have replaced, one of those should work.

Swapping L1 and L2 just reverses the operation of the switch so that UP becomes DOWN and DOWN becomes UP.

Julian F. G. W.

[jfgw]

An intermediate switch is essentially a double-pole changeover switch with some terminals combined. I suspect that one of the poles isn't switching.

IIRC, the switches have two terminals labelled L1 and two labelled L2. Normally, the switch connects thus:
In one position,
L1--L1
L2--L2
In the other position, the connections are reversed,
L1--L2
L2--L1
I suspect that, in your switch, one of the poles isn't switching. If, for example, the L2 pole isn't switching, you get:
In one position (correct operation),
L1--L1
L2--L2
In the other position (incorrect operation),
L1--L2
L2--L2
----L1 (not connected).
You will see that the first L1 and L2 are now connected to each other via the second L2. If this side of the switch is connected to the live and switched live (usually at the two-way switch), it will exhibit the symptoms described.

I think this is the most likely explanation although, without seeing and testing the circuit, it is impossible to be sure.

There are two different ways of wiring up two-way switches and I have only considered the most common method. The other method was more common with older wiring using single-core cables. Intermediate switches work the same with either method.

Julian F. G. W.

[RedSnapper]

Thanks all, really helpful.

(If you are not too far from Tunbridge Wells in Kent or Bude in Cornwall then I can help you!

Thanks for the offer but I fear I'm too far.

]PPS It could be that the intermediate switch has not been furnished with the connexion that is doesn't use. In which case what you'd be looking for would be two coonexions to each of the other switches (the third being connected elsewhere and not presented at the switch. Hope that makes sense.

Hah! Combined with the video from Hardgrafter I had an epiphany The wiring is the 'conversion' system, the upstairs switch is the intermediate, the halfway and the downstairs are 2-ways. The black in the halfway and the yellow in the downstairs are the common, meeting in a hidden box somewhere (hence the different colours).

Changed the wiring in the new switch to reflect this and bingo(ish)....the upstairs and downstairs switches work as they used to. The halfway still doesn't work right though.....if the lights are off it will work as a simple on-off and if on the other two switches don't affect it. If it is off and the lights are switched on by one of the other two switches then it doesn't work at all.

[RedSnapper]

An intermediate switch is essentially a double-pole changeover switch with some terminals combined. I suspect that one of the poles isn't switching...........

Thanks for that Julian, just need to get my head round it all as to what's wrong now.....we at least have it back to the 'usual' position of the upstairs and downstairs switches working fine which is the main thing as the halfway switch is rarely needed.