3 gang hall and 2 gang landing problem

2 Nov 2006
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United Kingdom
Hi, first time posting here so please be gentle.

Im having a problem wiring my hall /landing lights.

the 3 gang in the hall controls the porch, hall and landing, and is working fine.

However the landing switch controls the bathroom light and the landing light, its fine turning the landing light on/off however when switching the bathroom light on, it also turns a bedroom light on.

the bedroom light is a dimmer switch with red to common and black to L1, the landing switch has 5 wires..

2 black (red tape)
1 black
2 red

and is currently wired as follows...

Common Common
Red Black (taped)

L1 L2 L1 L2
Black (taped) Red Black

Can somebody help point in the right direction with how it should be wired to stop the bedroom coming on.

Any help appreciated
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Good post, clear and informative.

What exactly have you changed to create this problem? Has it always been like this? Is this switch plate a grid switch? (you mention a dimmer and a normal switch).

Which one of those blacks leaves the switch on its own? (there are 3 blacks and 2 reds, see where im coming from).

I think there will be a red and black pair to the downstairs switch, and a red and black to the bedroom light. The spare black will be to the landing light.

The red and black from downstairs goes to L1 and L2 on the landing switch, with the spare black on COM.

Then the red and black from the bedroom will go to the other switch on COM and L1.

It might be a simple case of swapping the blacks about if you dont know where they all go. Nothing bad will happen, you have no neutrals there to create a short, so trial and error is OK, but a multimeter and the knowledge to use it would be handy!
thanks for the reply.

im not sure what a grid switch is?

like you said though, red and black go to l1 and l2 with spare black going to com which makes the landing light work fine.

however the bedroom light comes on when the other switch is flipped to turn the bathroom light on, which blacks would i swap round? the spare black and the black in l1 (not the black in the landing l2 which works fine?) and where would i swap them to?
Have you changed anything else? I cant think what could cause this. Have you changed the bedroom light? Or altered any other wiring?

(apologies, i mis-read your clear informative post lol, i now realise the dimmer is seperate) ;)
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nothing else has been changed, does everything look in order? would it possibly be the switch downstairs that needs amending?
So this problem just emerged from nowhere? Or were you changing the switch?

I'm out of ideas. someone else care to have a shot?

All i can suggest is that you check the connections in the bathroom light and the bedroom light. Conductors do come loose and spring back to other terminals.
The switches were changed by my fiances dad when we moved into the house and have been like that since, it has been annoying the life out of me for sometime but still I have no idea where the problem lies.

Ive checked all connections and everything seems to look ok, but obviously something is wrong somewhere.

Sorry for the delay in replying!
A piccy would help.

The two gang switch you post a diagram of has three wires in one switch & two in the other, is that correct?

And you say the 2 way switch is working perfectly?

Is the landing/bathroom switch back-to-back with the bedroom?

If so, are there any wires linking the two switch boxes?

If the answers to these Q's are Y/Y/N and N, then I think we need to strip down that 2G switch & double check all the wiring to see what it does.

Can you tell me how these individual conductors are grouped into cables (with outer sheath)?

Is it twin red & three black singles?

Or two T&E's and one black single?

Or another configuration?

Turn the power off. Check with a two pole tester it is off. Remove the switch, noting what goes where.

Put choc blocks on each conductor. Restore power.
Test between all cores & earth. Note which ones read 230V. If it is wired as I suspect, then only one will be live when all the wires are separated.

Now turn the power off again. Loosen the other 2W switch off the wall, and disconnect the wires in the switch that partners the upstairs landing switch (make a note of what goes where, and leave the other switch intact).

If you only have one wire each in L1 & L2 do the following.

Now join the wires that are in the L1/L2 terminals together and go back to the landing switch at the other end. Use a continuity meter set to buzz to check across all wires in the switch you have completely removed. Hopefully, you will find two that buzz when connected across a continuity tester.

These will be the strappers for the two way switch circuit. These you know go to the L1 & L2 terminals in the top 2W switch.

The live feed will go to Common of the bathroom switch.

Now you should have two conductors remaining. One should be the switchwire for the landing, and the other, the switchwire for the bathroom.

In turn, join these to the live feed you have terminated into the Common of the 1W switch.

Turn off (if it isn't off already - check first) and join one switchwire to the live & turn on again. Do the same with the other. What happens?

Hopefully, you will be able to ID the switchwires. The bathroom switchwire goes to the L1 of the one way switch and the landing switchwire goes to the Common of the two way switch.

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