2 way light switch problem after building work

[katheh]

So as far as I understand it this is what I have so only one of the four switch position combinations will turn the light off because somewhere (but seemingly not at the switch) there is short between Com and L1 or L2.

In this diagram only LHS up, RHS down will break the circuit.

 

[Mikefromlondon]

This is an interesting puzzle, really doing my head in as well, but Bear with me a little, I will see if I can tell you what exactly is the situation that can cause those logical conditions as I certainly don't want to get it wrong again.

( right now I have someone visiting me, so in about an hour see If I can show how it was possible with one switch being at fault)


Last night I drew about 5 different configurations that one of them would cause similar pattern with one switch contacts being faulty i.e shorted out permanently.

 

[katheh]

Thanks, this is doing my head in too. I think the diagram I drew covers what I have. The thick black line represents the shorted switch.

The mystery is that both switches have been swapped for others and I still have the same problem so it must be shorted out somewhere else.

 

[Mikefromlondon]

OK, I have got it.
I will draw it up show on here,
there are two conditions why this is happening,
A. One of the contacts on one of the switches is shorted out
B. Live is being fed to L1 or L2, and not common

 

[katheh]

OK, I have got it.
I will draw it up show on here,
there are two conditions why this is happening,
A. One of the contacts on one of the switches is shorted out
B. Live is being fed to L1 or L2, and not common

Thanks that would be great.

I get option A as it is the same as I drew further up, but the switches have been replaced with others with same result.

Option B is puzzling me. Every time I draw this I get the light off in 3 out of the 4 switch combinations which is the opposite of what is happening.

 

[Mikefromlondon]

I can't post a picture as my account is closed (Or I was using a friend's account and can no longer access it) how can I send you a png file so that you can post it here?
can I attach a file to your email that you can PM me.

( going to ring my mate see if he can give me his new password so I can post here)

 

[katheh]

Just PM'd you email address

 

[Mikefromlondon]

sent you my sketch to your email. If you would be so kind to post it here for me thanks much.

 

[katheh]

Diagram from Mikefromlondon

 

[Mikefromlondon]

Thanks, this is doing my head in too. I think the diagram I drew covers what I have. The thick black line represents the shorted switch.

The mystery is that both switches have been swapped for others and I still have the same problem so it must be shorted out somewhere else.

I agree the short can be anywhere, if it is not within the switch contact.

 

[bernardgreen]

If there is a hidden junction box then this is one option for a mis wire

 

[Mikefromlondon]

If there is a hidden junction box then this is one option for a mis wire
View attachment 95983

very helpful suggestion indeed.

Your layout achieves the same logical conditions yet does not require a shorts in wiring or switches. Good one Bernard.

I wonder if OP can tell us since when did he start getting this problem, and whether at one time it worked OK as a 2 way switch should do.


Sorry again i rushed too quickly, yes there is a logical flaw, when both switches are down the light will be off so not quite like what my layout does, still time to ponder Bernard.

 

[katheh]

Absolutely, before the building work started these switches worked 100% correctly.

The house was rewired in 2008 and all switches replaced with new. Would an electrician at that time put a junction box somewhere inaccessible (assuming he followed the rules)?

 

[Mikefromlondon]

Bernard, found what is wrong with your ;layout, if you move your blue lamp wire to middle rail in the junction box and your Live to bottom rail then you will achieve perfect logical function Op is having and without any short circuit switches.

Now we know where we are, we can take it from here to try and resolve the issue, would be nice if you could redo a new layout and post it below. leave the other one there.

 

[katheh]

Bernard, found what is wrong with your ;layout, if you move your blue lamp wire to middle rail in the junction box and your Live to bottom rail then you will achieve perfect logical function Op is having and without any short circuit switches.

Now we know where we are, we can take it from here to try and resolve the issue, would be nice if you could redo a new layout and post it below. leave the other one there.

Yes, that's it. Now all I need to do is convince the electrician that he must have rewired the junction box. I have just found a junction box in the roof space with at least 10 cables going into it.