Wiring Puzzle

17 Mar 2014
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United Kingdom
In my hall, I have a 3 gang switch with 1 operating as 1 way (cupboard under stairs), and 2 operating as 2 way (stairs/landing and hall).
I also have a 2 gang switch with 1 operating 1 way (porch), and 1 working 2 way (hall)
The 3 gang works OK for the cupboard, and the landing.
The 2 gang works OK for the porch.
To get the lights on in the hall, both switches on the 2 gang must be off (porch and hall), then switch on with the 3 gang.
If the porch light is used while the hall light is on, the hall light goes out.
Sounds to me like there is a mis-wiring in the 2 gang switch.
Has anyone got any clues??
This is something that I have put up with for a long time, but thought there might be an easy fix.
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Post photos of teh wiring to both switches and pls make clear which switch does what. Someone may be able to figure it out for you.
It could be an easy fix but it may not be, would depend if the installer of the circuit actual fitted the circuit so it could function as a two way on it's own right.
To help us you will require to upload some pictures of the terminal connections and cables within both switch plates and have some test equipment that can test for continuity and voltage, a multi-meter would be suitable.
It's a guess without the pics, but your description suggests that the 2 core strapper from the 3 gang (which is C connected to permanent live) has been misconnected at the two gang end (where C goes to the lamp). If one of the strapper wires has been connected to the porch switch it would give the effect you mention. This may have been done deliberately when the person fitting the porch light found that they had no power supply tp feed the switch to the porch, or you may be lucky and find a simple wrong connection. Suggest first port of call is that 2 gang switch.
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Thanks for all the interest, here are the photos - hopefully.
The 3 gang is hand to see, as there was hardly any slack, in a very shallow back box, but as the last person said, I believe the problem is in the 2 gang switch.
I'm afraid the pictures aren't clear enough.

We need to see exactly which terminal each wire enters and

which cable (grey sheath) each wire comes from.
In the 2 gang, which is the one behaving more oddly, the red and black to the front switch are from the same grey cable, and similarly the rear red and black are from another grey cable.
Both reds are attached to com, both blacks are attached to L2, and there is a link between the two L1s.
Without the link, the hall doesn't work at all, and the porch works as before.
In that case move the hall red wire from COM to L1 (of the same switch) and

fit the link between the two COMs along with the remaining red in COM
Star player!!
Thanks very much. That's been annoying me for years, but not enough to get someone in.
I had electricity put out to the garage a couple of months ago, and was going to get the electrician to have a look while he was here, and totally forgot.
Thanks again.

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