Help with light switch wiring

[UnusualCapybara]

Hi All,

I've got a confusing problem which has been testing me for most of the day and I'm now ready to admit defeat and ask for help!

This switch in my porch controls 2 sets of lights and I assume there are some junction boxes hidden in the ceiling or in the wall somewhere but this is a new house for us and I didn't put them in, so have failed to find them.

1. An outside wall lantern (the thin blue/brown pair)
2. Some outside low level lights on the driveway (thick blue/brown pair)

When I test across the thin blue/brown pair I get 240v on a multimeter and if I drop these into a single gang switch with brown in common and blue in L1, I get the expected behaviour and everything is fine.

However, the thick brown and blue pair carry no voltage on testing with the multimeter.

If I bundle them all into the same switch (2 blues to L1, 2 brownto common) I get weird behaviour in that flicking the switch one way will turn on the wall lantern, flicking it the other way will turn off the wall lantern and turn on the low level lighting. They can never be on or off at the same time, one is always on.

Now on the verge of madness, any help appreciated.

 

[mrsplodge]

Was it working before? If it was, how was it wired? My guess would be that the thin wires are switched live from your light, and so the thin blue should be sleeved in brown, and the thick ones are live + neutral and so need to be connected to a supply. I think this would also explain the behaviour when you connected both to the switch. But that's just a guess without knowing more about how it was previously wired up. Also, do I see a third cable on the right of that box?

 

[mrsplodge]

Actually, thinking about it, it might not explain the behaviour.

 

[333rocky333]

The behaviour suggests you have somehow put the two circuits in parralel somehow

 

[conny]

The behaviour suggests you have somehow put the two circuits in parralel somehow

Surely if they were in parallel they would both come on or go off at the same time?

I suspect thet one of the blues is switched live and one of the browns is the other switched live.
Have you tried the thin blue with the thick brown and the thin brown with the thick blue? Might be worth a try.

 

[Harry Bloomfield]

The behaviour suggests you have somehow put the two circuits in parralel somehow

Series?

 

[333rocky333]

Oops sorry, Series

 

[mrsplodge]

Have you tried just the thick ones in the switch?

 

[SUNRAY]

If you linkthe thin wires together (as you did by wiring them to a switch) do either of the other wires become liive?

 

[SUNRAY]

Actually, thinking about it, it might not explain the behaviour.

I think it could easily be the situation, especially if the lantern contains a standard bulb, such as a 60W and the low level lights are say 2W LEDs

 

[UnusualCapybara]

Thanks a lot everyone for the suggestions, this continues to beat me. I've never actually seen these lights work which was the reason for my initial investigation but this morning I've wired the whole thing up exactly as I found it and tested it again. The long and the short of it is that I can have the outdoor low level lights on, but that makes the wall lantern go off and vice versa.

Similar types of bulb/output in both the lantern and the low level lights - 42w LED E27 bulbs.

I've tried swapping combinations of the fat blue / thin brown and fat brown / thin blue but get the same behaviour.

I'm a bit confused by the total lack of voltage across the thick blue/brown pair. At face value it's almost like these are just a live and neutral looking for a feed but that also makes no sense as they wouldn't be wired into a switch in that case

Continued suggestions welcome

Edit: Thick blue/brown only in the switch does nothing at all. No wall lantern, no low level lights.

 

[SUNRAY]

Did you see this:

... Also, do I see a third cable on the right of that box?

 

[EFLImpudence]

I'm a bit confused by the total lack of voltage across the thick blue/brown pair. At face value it's almost like these are just a live and neutral looking for a feed but that also makes no sense as they wouldn't be wired into a switch in that case

You do realise that if you have two wires at 240V your meter will read 0V?

you should be testing each wire to earth and then continuity between them.



42W LED ???

 

[UnusualCapybara]

Did you see this:

Sorry missed this one - there is another cable, its a 3 core (black/grey/brown) which I *think* is connected to a secondary switch in the hallway. I took detailed notes and pictures of both switches before touching them so I've put everything back exactly as it was. The complete layout of the porch switch as I found it was:

Com (top): Fat brown + brown from thin T&E
L2 (top): Fat blue + blue from thin T&E
L1 (top): Empty
L2 (bottom): Black from 3 core
L1 (bottom): Grey from 3 core
Com (bottom): Brown from 3 core

 

[UnusualCapybara]

You do realise that if you have two wires at 240V your meter will read 0V?

you should be testing each wire to earth and then continuity between them.



42W LED ???


View attachment 325541

Thanks for this - as someone who didn't own a multimeter 48 hours ago this is an education!

And by 42w LED what I probably meant to say was - an LED bulb with equiv. 40w output approx.

I've tested each wire to earth with the following results:

Thick Blue: 4.9V
Thick Brown: 4.9v

Thin T&E Blue: 3V
Thin T&E Brown: 252V

3 Core Brown: 252V
3 Core Grey: 252V
3 Core Black: 0.8V.

I'm not sure I fully understand the role of the 3 core cable at this point but what these tests suggest to me are:

1. The thick T&E isn't live at all
2. The Thin T&E is a Constant/Switched live pair