Light circuit intermediate switch - what's up?

[khartim]

I have three switches controlling one set of of lights on the upstairs lighting - one each end, and one downstairs. We have been living here several months and never noticed a problem, but a few weeks ago, I noticed that the intermediate switch did not work when the downstairs switch was in up position. I changed out the intermediate switch and the problem remained. So I investigated all positions of all three switches.

If '1' represents toggle up and '2' represents toggle down, with the intermediate switch in the middle, I get the following results.

111 ON
112 OFF
121 ON
122 ON
211 OFF
212 ON
221 ON
222 ON

Whenever intermediate switch is in the '2' position the light is ON regardless of the position of the other switches.

Anyone seen this before? Is there an obvious explanation that I can smack my forehead to? This is a new switch, and statistically unlikely to have exactly the same fault as the previous switch I changed out.

(I have temporarily misplaced my multi-meter and don't really want to buy another, as the old one is bound to turn up in a kitchen cabinet, behind the sofa, in sock drawer...)

Thanks in advance!

 

[sparkwright]

Tell us EXACTLY how each switch is wired please. Photos if possible.

 

[khartim]

Pix of one of the end switches and the intermediate switch. Two cables come into the intermediate switch, each with black, grey and earth. One cable wired to left handside of switch, the other to the right. Top terminals are both labled L1, bottom terminals are labled L2. Greys to L1 and blacks to L2

End switch seems wired OK. Grey to L1, black to L2.

 

[sparkwright]

At the intermediate switch, I would expect one black and one grey wire from the same cable to go in the top two terminals.

And then the black and grey from the remaining cable to go in the bottom two terminals.

(The browns joined together in a separate connector block.)

 

[khartim]

Well that was easy! Done. Thanks very much. I should have been able to work that out myself. But then again, obviously I am a bit challenged in that department...

Much appreciated.

 

[khartim]

Spoke to soon.... Not fixed, just not functioning in a slightly different configuration. Now we have:

111 OFF
112 OFF
121 OFF
122 ON
211 OFF
212 ON
221 OFF
222 OFF

Any thoughts?

 

[sparkwright]

What is the wiring at the third switch? (You have only sent two switch photos.)

 

[sparkwright]

Also, can you confirm what terminal markings are embossed on the back of the intermediate switch (so we can be certain)...

 

[khartim]

Top of intermediate switch two terminals both labelled L1. Bottom two terminals labelled L2.

Here is the third switch. I hadn't realised it is wired differently to the other end switch.The switch connected to the circuit in question is the one at the bottom. Black and a blue with a black sheath are connected to one one terminal, grey and brown to the other. I presume these effectively route to the lights, and are switched on their return to link up to the solitary brown at the top, which I assume is the common.

 

[sparkwright]

Can you confirm on both 'end' switches that the brown COMMON wire comes from the same cable that accommodates the black and grey?

 

[khartim]

Yes, confirmed.

 

[sparkwright]

CHECK ALL CONNECTIONS ARE SOUND, INCLUDING THE TWO BROWN WIRES AT THE INTERMEDIATE.

It's hard to diagnose without being there, and the fact you don't have a multimeter, but wiring connections 'seem' as they should be.

You could try removing the intermediate switch, just to see what happens.

You would need some connector blocks to temporarily bypass the wires.

You would connect both blacks to a connector, and both greys to a connector.

You would then see if the two end switches behave correctly.

 

[EFLImpudence]

From the second sequence in post #6

111 and 221 are wrong. The light should be ON.

As you see the ONs add up to odd numbers and the OFFs to evens.
This is not definitive and could just as easily be the other way round depending on the terminals used.

Therefore, because the common factor is the right hand '1', I would think you have either -

not connected one of the wires to the intermediate switch correctly, OR
one of the wires is loose on the switch which corresponds to the right hand '1' in the sequence, OR
that switch or the intermediate is faulty.

 

[khartim]

Thanks all for the input. Too dark on the landing to investigate further tonight. Tomorrow is Chinese New Year's day. Happy Year of the Tiger! We have the family around tomorrow for celebrations, but I will continue investigations on Wednesday.

Kung Hay Fat Choi!

 

[khartim]

Sorted. Lazy mistake of thinking I was trying to correct the same fault each time, when I was dealing with three faults. Each time I fixed the issue at hand, I introduced another. Physical fault → incorrect wiring → sloppy wiring.

Original switch had a physical fault (Much later I took it apart - the switch's plastic rocker had snapped.)

When I replaced it with a new switch, I wired it wrong. When the light still didn't respond properly I mistakenly assumed I was still searching for the same problem.

When I rewired following sparkwright's advice, it seemed to work, so I screwed it back into the wall. Then I discovered it wasn't really working. So I scratched my head and took a break.

Then my multimeter turned up. I decided to get to the bottom of it and took all the switches out of their wall boxes to examine all the wiring, and immediately saw that one of the travelling wires in the intermediate switch was just hanging loose totally disconnected. So that was it. No need for the multimeter.

All switches back, functioning as they should. Thanks sparkwright for the advice that fixed the problem and thanks EFLimpudence for the handy trick to calculate which combinations should result in OFF and ON.