2 way light switch problem after building work

[EFLImpudence]

I'm a bit wary of criticising after last night's mistake but I do not think any miswiring will cause the effects.

As I see it Katheh's and Mike's diagram is correct but if the switches are all working properly then a short in the cable between the relevant wires is the problem.

 

[katheh]

I'm a bit wary of criticising after last night's mistake but I do not think any miswiring will cause the effects.

As I see it Katheh's and Mike's diagram is correct but if the switches are all working properly then a short in the cable between the relevant wires is the problem.

I'm thinking this too as electrician is adamant that he didn't see or touch the junction box. I have no reason to disbelieve him as all the junction boxes he installed are easily accessible so why wouldn't he just fix it if it was that easy.

Any idea what could cause the short? Builder says they never tripped the circuit which I guess you would expect if it got a nail through it?

 

[EFLImpudence]

No it would not trip as both wires are Lines(lives).

What work was done? Any screws/nails above the switch or in the room above?

 

[Mikefromlondon]

Efl, have a look at Bernard's layout, provided he moves his switched wire (the blue to the lamp) to middle rail in the JB, and Live to the bottom rail in the JB, his logic then works exactly right as per OPs situation, and this is without the need for a short anywhere, so although my layout only meets the logical status with a short, Bernards does not require a short as long as you move those connections I mentioned above.

hence I think Bernards amended layout would be the likely case, but then again who knows until one gets there to find out it could be either, now how OP's electrician solves the problem depends on his ability to figure out or trace individual cables, isolate them from switches and marks each run and then rewire as a 2 way switch should be wired.

(BTW I do not criticise anyone, no one is perfect, sometimes even a team of highly qualified scientist can get things wrong the first time, and can take several attempts to get it right.)

 

[katheh]

No it would not trip as both wires are Lines(lives).

What work was done? Any screws/nails above the switch or in the room above?

Aha it wouldn't trip. No work above. The weird thing is that no work was done between the switches and the light. A wall was removed and new ceiling was plaster boarded about 1m from the light but in the opposite direction to the switches. No idea where the mystery junction box is.

 

[EFLImpudence]

Efl, have a look at Bernard's layout,

Ah, Ok.

Just to mention both commons have a brown wire so it would require some colour-blindness to replicate the miswire at the JB.
I think I shall give up as there seem to be several options so it will require investigation on site.



I shall just show this diagram I was doing. It may help Katheh.

 

[bernardgreen]

provided he moves his switched wire (the blue to the lamp) to middle rail in the JB, and Live to the bottom rail in the JB,

This puts the two lower switch contacts in parallel and the top contacts are redundant. The fault is the left hand switch has the wires to COM and L1 ( or L2 ) reversed as in the sub diagram. The wire may be reversed in the junction box and not at the switch.

 

[EFLImpudence]

Just one more thought:

The light is not always on.
It is just on when both switches are down - when it should be off.

 

[katheh]

provided he moves his switched wire (the blue to the lamp) to middle rail in the JB, and Live to the bottom rail in the JB,

View attachment 96015

This puts the two lower switch contacts in parallel and the top contacts are redundant. The fault is the left hand switch has the wires to COM and L1 ( or L2 ) reversed as in the sub diagram. The wire may be reversed in the junction box and not at the switch.

Are you saying it's worth trying swapping L1/2 and com at the switch?

 

[katheh]

Another thought, would a multimeter help diagnose the problem or would it just confirm what we know?

 

[Mikefromlondon]

Katheh, unfortunately the nature of this fault is complex, no shifting around of wires within the switches will resolve your problem, going by Bernards corrected diagram, even by swapping wires from say com terminal to top L1 on say the left switch will still yield the same logical conditions, or if you also swap wires on the other switch, it will give you slightly different logical conditions, but will never give the desired 2 way switching conditions.

Get your Electrician to trace wires in the JB and mark them and reconnect them correctly.

 

[endecotp]

With a multimeter and a methodical aproach I'm sure it could be worked out.

 

[bernardgreen]

going by Bernards corrected diagram,

It was correct as a two way circuit to begin with,. I modified it to be as you described the change which meant it was no longer a two way circuit but simply two switchs in parallel. Either switch down would put the light on

up up OFF
up down ON
down up ON
down down ON

 

[katheh]

going by Bernards corrected diagram,

It was correct as a two way circuit to begin with,. I modified it to be as you described the change which meant it was no longer a two way circuit but simply two switchs in parallel. Either switch down would put the light on

up up OFF
up down ON
down up ON
down down ON

You sir are a genius. It's fixed!! Swapped L1 and Com on both switches.

The only mystery that remains is who the hell rewired it in the first place???

 

[EFLImpudence]

BOTH switches ?

I am glad it is fixed but I must admit to being totally confused.