DIY Doctor

Two way switch not wired correctly

Postby Biver » Sat Apr 10, 2021 11:19 am

I have a hall light which is controlled from two switches, upstairs and downstairs. Everything works individually but the two-way is not behaving. When either upstairs and/or downstairs is on, the light is on, but it can only be turned off if both are off. Weirdly, if I hold the upstairs switch halfway between on and off, the light will turn off successfully, but apart from that there doesn't seem to be a way to turn off the light unless both are in the off position.

The upstairs light switch looks pretty simple and appears to be set up for a two-way switch:
Up_01.png
Upstairs single gang two-way switch

Up_02.png
Upstairs labelled wires. I've coloured the wires based on which wire they have come from in the wall.


The downstairs is a three gang switch. The right two are one-way switches but the left switch should be two way and should be partnered with the upstairs light.
Down_01.png
Downstairs three gang. Left-most should be two-way alongside upstairs switch. The two on the right should be simple one-way switches.

I think there are enough wires to make a proper two-way connection but my guess is that the "G" and "I" wires shouldn't go into the same port on the central gang.
Down_02.png
Downstairs labelled wires. I've coloured the wires based on which wire they have come from in the wall.


I am struggling to figure out how to rearrange the wires to enable the two way switch to work properly. If anyone can help I would be really, really grateful.
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Postby ericmark » Sun Apr 11, 2021 3:33 am

There are two ways to wire up two way switches, at school we were taught this [attachment=0]two-way-school-boy.jpg[/attachment] method, however this means a connector block and so in the main we use this [attachment=1]two-way-real.jpg[/attachment] method, it will be noted the Com wire does not connect to anything other than the other switch.

There was a method used years ago where the line was borrowed from another light circuit, this can cause interference with some hearing aids, but worked OK when up stairs and down stairs were fed from the same MCB/fuse, but latter there was a move to split the feeds up and down stairs and this caused a borrowed neutral situation, so often the two way system was disabled when the lighting was split.

There are kinetic switches to get around the problem, but not sure if you can get three switch plates.
Attachments
two-way-school-boy.jpg
School boy method
two-way-school-boy.jpg (34.16 KiB) Viewed 311 times
two-way-real.jpg
Normal two way
two-way-real.jpg (47.51 KiB) Viewed 311 times
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Postby Biver » Sun Apr 11, 2021 7:03 am

Thank you very much for the quick reply. I'm struggling a bit with recognising which wires in your cartoon correspond to which in my photos. If anyone is able to identify them for me so that I know which to switch I would be really grateful.

By the way, I noticed an error in my original post. It should read:
"...but my guess is that the "H" and "I" wires shouldn't go into the same port on the central gang."

Biver wrote:I think there are enough wires to make a proper two-way connection but my guess is that the "G" and "I" wires shouldn't go into the same port on the central gang.
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Postby Mr White » Sun Apr 11, 2021 9:48 am

Without being there to test it, I would say that you should take the back wire that has red sleeving from the C terminal and connect it to the L2 terminal which currently has no wire at all.
Leave the other red wire in the C terminal.
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Postby Biver » Sun Apr 11, 2021 3:28 pm

This worked! Thank you very much, Mr White
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Postby Mr White » Sun Apr 11, 2021 8:22 pm

(I figured it would) Thanks for letting us know, most folk post and go. Next time you change a switch, may I suggest you mark the cables, and then take a couple of pictures.
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