Changeover switch acting as master

hashamyim · Feb 14, 2023

Hey - I had a workman come round this morning and he had to detatch the light switches. Afterwards, he put them back on again, but something seems to have changed and I know that I need to swap two wires around but not sure which...!

In the hallway, I have one light that is controlled by two light switches. Currently, the switches are wired as follows:

Switch one: Top left blue, Top right white, Bottom black.
Switch two: Top left brown, Top right white, Bottom brown. (It is an old flat, so I'm not sure that the colours on this switch are per the norm)

However, in this constellation, although switch one works properly, switch two acts as a master, i.e. switch one only works if switch two is on:

Switch two = on... Switch one can be used to turn the light on or off.
Switch two = off... The light is off regardless of what position switch one is in.

I assume I just need to switch around the two top wires in switch one, but I wanted to check it with people in the know first...!

Thanks! Hashamyim

brianmoooore · Feb 14, 2023

Close up pics of the back of the switches would help.

hashamyim · Feb 15, 2023

Sure! Please see attached!

brianmoooore · Feb 15, 2023

These are known as 2 way switches in the UK. There's two different ways of safely connecting these up, but in both arrangements the two wires at the top of one switch connect to the two wires at the top of the other switch, and are known as strappers.
In your case, the colour of the wires is not the same at each end, so there must be joints somewhere between them, which confuses the issue, and prevents us giving a definitive answer.
Given that there are three different colours at the first switch, there's a good chance that they have been returned to their correct places, but with the second switch there are two browns, which could easily have led to a mistake, so, I would try turning off all the power to the house, then swapping over those two browns.

hashamyim · Feb 15, 2023

So, I tried swapping over the browns in switch 2 and now the roles have reversed, i.e. switch 1 now has ultimate control (as master) and switch 2 will turn it on/off as long as switch 1 is on (if switch 1 is off, nothing happens regardless).
Not sure what that tells us...!!

brianmoooore · Feb 15, 2023

Right, I think I've worked out which version of two way wiring you originally had, and think I've worked out how it's wired now!
If I'm right, switch 1 is correct, but on switch 2 both browns should be at the top and the white at the bottom. The circuit should work with the two browns either way around, but one way will result in the light being on when both switches are either up or down, and with the other way, the light will be lit when one switch is up and the other down.
Turn off the power before moving any wires.

hashamyim · Feb 16, 2023

brianmoooore said:
Right, I think I've worked out which version of two way wiring you originally had, and think I've worked out how it's wired now!
If I'm right, switch 1 is correct, but on switch 2 both browns should be at the top and the white at the bottom. The circuit should work with the two browns either way around, but one way will result in the light being on when both switches are either up or down, and with the other way, the light will be lit when one switch is up and the other down.
Turn off the power before moving any wires.

Ah fantastic, thanks - will give it a go when I get back from work this evening and let you know

hashamyim · Feb 25, 2023

brianmoooore said:
Right, I think I've worked out which version of two way wiring you originally had, and think I've worked out how it's wired now!
If I'm right, switch 1 is correct, but on switch 2 both browns should be at the top and the white at the bottom. The circuit should work with the two browns either way around, but one way will result in the light being on when both switches are either up or down, and with the other way, the light will be lit when one switch is up and the other down.
Turn off the power before moving any wires.

Hey there! So, realise this has taken a lot longer than expected but I had time to try it yesterday and you'll be glad to hear that you were right and it works!!! Thanks ever so much and sorry again for the delay in getting back to you. This renovation malarkey really is a time-consuming thing lol
Hope you have a great weekend.