2 way light switch problem after building work

[EFLImpudence]

Possibly, Efl, but I drew the 2 way switch schematic on a piece of paper and wired the live to one of the L1 terminals

So did I..

and from it you could clearly see you would get exactly the logic pattern that has been described by OP. (Sorry didn't intend to prove anyone wrong or anything just trying my bit to help)

Not at all.
However, as the two coms must be connected for the light to work it doesn't matter which is the incoming or outgoing.

Often if one jots down a problem on paper, it can become more apparent, other times experience would kick in and say yup i know what the problem is, but one can only get experience if thousands of 2 way circuits were wired incorrectly and one had to fix them on a daily bases.So theory cuts in.

Perhaps I should have just known - but didn't.

 

[EFLImpudence]

I'll rephrase that _

However, as the incoming and outgoing wires must be connected for the light to work it doesn't matter which is the incoming or outgoing.

 

[Mikefromlondon]

Unfortunately, no if the lamp wire was connected to either L1 or L2, the same logic conditions do not occur, just tested my theory so incoming live is the culprit and is wired to either L1 or L2 on the switch that has the incoming live. (just confirming efl)

(why it wouldn't follow OP's logic, if the light wire was not connected to Com (correct way) and if it was connected to either L1 or L2, (incorrectly) then that would mean the light would only come on with just one switch and not with either switch.)

(Please EFL, I am not having a Contest with anyone.)

 

[EFLImpudence]

(Please EFL, I am not having a Contest with anyone, just trying to solve a logical challenge, which I enjoy trying to solve)

No, I know. So do I.

My head is beginning to swim.

I was forgetting that when this happens, the upstairs switch will turn the lights off so

does that mean it is the downstairs one which is the problem?

 

[EFLImpudence]

Yes, you are correct. My apologies.

I drew the diagram wrongly.

 

[EFLImpudence]

Now I've drawn it correctly I can't get it to work at all.

 

[Mikefromlondon]

Efl, sorry you were also right, I owe you a big apologies, I forgot to mention that my logic was based one one of the contacts remaining in permanent ON state, (or shorted out) so I failed to state that above and got carried away with swapping wires over, yes indeed you were right that one of the switches is at fault. the switch has a permanent short on it, and again it is impossible to tell which one . and it seems that the wiring is correct. And you were also right about if you were to swap lamp and live wires, the logic would still be right yes indeed.

Efl I owe you one, Thanks given.

 

[EFLImpudence]

 

[Mikefromlondon]

Thanks a million and really apologies for being too hastily in concluding the switch problem to wiring problem, when junction box was mentioned, I thought what if the wiring was removed and then rewired incorrectly, that lead me astray!

 

[EFLImpudence]

I think my wrong diagram resulted in replicating your short.

Katheh - I think one of the switches is faulty.
Don't bother rewiring; just try a replacement switch.

 

[katheh]

Thanks for the replies. I was trying to get my head around how the switches could be wired incorrectly and also concluded that somewhere one switch is permanently on.

So this morning I took a switch from elsewhere in the house that is definitely working and swapped it with each problem switch one at a time. No change to behavior.

Also checked both problem switches on another single switch light fitting (both Com to L1 and Com to L2). Both worked perfectly.

My conclusion is either:

1. Wiring at junction box has changed. The rewiring involved removing a secondary fuse box and connecting more lights to main house circuit. Could have connected them to this junction box and wired it back together wrong possibly?

2. There is a nail through a wire somewhere causing it to short out one switch. Does this sound feasible?

 

[katheh]

So if that's the cause, and we assume (reasonably??) that it wasn't like it before, who changed it?

I can only think that it must have been inadvertently rewired somehow.

Nobody "inadvertently" unscrews switches and swaps wires over.

Did the building work involve any painting of the wall(s) the switch(es) are on?

I am 100% certain switches worked properly before. Used it every day for 2 years. Noticed problem (not testing, just noticed through normal use) within 2 hours of electrician leaving house.

I was thinking the junction box might have been changed to add more lights to the same circuit but I'm no electrician so don#'t know if this is likely or not.

Yes, decorators were in too on same day as electrician although it looks like they just masked around the switch as paint behind it is old colour. Other switch was in room not decorated.

 

[securespark]

Is the LHS of the ground floor switch the one operating the landing light?

Usually it is the RHS that is used.

Can we see the connections at the other set of terminals?

 

[katheh]

Yes, so it's not actually a landing but a hall way between living room and downstairs bedrooms (chalet bungalow). 2 gang switch is in the dining room next to door. LHS operates hall light (the problem light). RHS operates living room light which also has a 2 way switch. Living room light works perfectly from both switches. I will get a photo of the other side.

 

[katheh]

Here is the RHS of the 2 gang switch. This operates living room light which works fine.