Extra switch to existing 2 way setup

25 Feb 2005
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United Kingdom
Hi. I already have a 2 gang 2 way switch at the foot of the stairs operating lights at top and bottom of stairs, and a 1 gang 2 way switch at the top of the stairs operating the light at the top of the stairs.
I would like to add a switch near the front door to switch on the down stairs light when entering the house. What is the simplest solution?
If possible I would like to use a 2 gang switch so that one switch does the downstairs hall light and the other would do the external porch light.
Thanks in advance.
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In your existing downstairs light switch you should find two wires, one in COM and the other in either L1 or L2. Move the wire from COM to the third, unused terminal. DO NOT move any wires in the other switch.

Put it back together and check that your upstairs light still works as before and that the downstairs one doesn't. You can skip this test if you're confident of your switch wiring abilities.

Run a three core twin and earth cable from the downstairs switch to your new switch. Link each terminal to the matching one in the new switch, ie COM to COM etc. DON'T FORGET THE EARTH. I believe it's traditional to use yellow for COM and of course you put red in whichever terminal already has a red in it. Blue goes in the third one which probably has a black wire already. That's it. There's probably a drawing of this somewhere on the forum.

If you want a double switch by the front door that's no problem. Wire the two halfs as if they were two independent switches - which they are.
Many thanks Felix. I will get right on it - as soon as I finished chasing the wall. I hate this bit!
Thanks again.
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Oops, I missed that one. Oddly enough, three other electronics engineers around here had to think about it too!
felix said:
Oops, I missed that one. Oddly enough, three other electronics engineers around here had to think about it too!
sorry to be picky, "electronics engineers" are not electricians
That's quite true. Moreover, I've never seen flat twin and earth used inside a linear accelerator (which is what we fix here) still less the three core variety! I guess all our knowledge of such things came from DIY books.

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