2 way switching, 2 wire control, lighting problem

[BabyT]

Hoping for some advice.

My landing light stopped working (then started working again a week or so later and then has not worked for the last few months). The bulb is fine as I've checked it elsewhere.

From what I've been able to discover I believe my house uses a 2-way switch, 2 wire control wiring system (or cable saving system) for my landing light.

Two red switch-live wires (plus an earth) go from the downstairs switch (L1 and L2) in my hallway to the upstairs switch (L1 and L2) in my landing. A single red switch-live wire (plus an earth) then goes to the landing light. In addition, a single black wire goes from my landing light, into my roofspace and then disappears down the wall between my landing and my bathroom. I've not been able to find out where it then goes to.

My understanding was that this black wire should be the neutral wire, but what I've noticed is that when power is going to the light (i.e. the red switch-live wire has power in it) the black wire also has power in it (I'm only using one of the electrical tester screwdrivers to check for power). This occurs whether or not there is a bulb in the light fitting.

I had also thought that the power should only be able to get to the black wire by going through the bulb (to continue the circuit) so I removed the 3-spotlight light fitting and attached a simple pendant fitting but the same issue occurs.

Any ideas as to what the problem is and how best to resolve it so that my landing light will work again? Grateful for any feedback.

 

[ProDave]

I think you are correct that the black should be neutral, and is currently floating.

You need to find where it goes and re connect it. Start by looking in the back of all ther switches in the vicinity of the wall it goes down into.

 

[bluetobits]

If you can't find it behind any switches as Dave suggests, try the sockets, as i wouldn't be surprised if it's been robbed from one of those 

 

[Murdoch]

hum.... me thinks without a proper tester and a wander lead this thread could run and run.....

 

[Davethsparky]

A broken and floating neutral such as this can be extremely dangerous as parts which would not normally be live are. Be very very careful if you are attempting this job yourself, electricity takes a fraction of a second to kill a healthy person and you don't get a second chance. 

 

[Sharpend]

Could this not be induced voltage showing? I understand this is a neon screwdriver being used to test with? In which case it may not be anywhere near 240v, although advice would be to proceed with caution or obtain correct tester to test with. 

 

[bluetobits]

Has any work been done in the property recently? It might be easier to narrow down the cause of the fault if so.

 

[BabyT]

Hi,

Thanks for all the replies. No work has been done recently but I'll hopefully get a chance this weekend to have a (very careful and cautious) look to see if I can find out where the floating neutral wire goes to.

 

[Davethsparky]

Hi,

Thanks for all the replies. No work has been done recently but I'll hopefully get a chance this weekend to have a (very careful and cautious) look to see if I can find out where the floating neutral wire goes to.

Confirm that it is floating first and not just a capacitively coupled potential

 

[BabyT]

Confirm that it is floating first and not just a capacitively coupled potential

How do I do that?

 

[Davethsparky]

How do I do that?

With a suitable approved voltage indicator as used for safe isolation. A Drummond test lamp or similar is quite good for this.

 

[ProDave]

Confirm that it is floating first and not just a capacitively coupled potential

If his electrical test screwdriver is showing a voltage on it, then you can be pretty damn sure it is not connected to neutral.

 

[BabyT]

Hi all,

A frustrating weekend.... Checked as many light fittings and switches as I could, and besides tidying a few connections which didn't look the firmest, I couldn't find the other end of my floating neutral. My current thought is that it's above the wood panel ceiling in my kitchen or in the floorspace above my living room.

Anyway, after turning the power back on my landing light now works (no idea why) but my outside and hall lights no longer work (these run off the 3-gang switch in my hallway that also works the landing light) and neither do the 3 lights in my living room (which run off off single dimmer switch that backs onto the 3-gang hall switch).

Totally baffled and think I'll have to resign myself to calling in an expert.

Thanks for all the advice though. 

 

[BabyT]

After much hunting found a loose neutral connection in my dining room light. After finding and fixing a couple of other issues along the way my lights are all now working as they should.

Thanks again for the advice.

 

[ProDave]

That's good. At least the neutral is borrowed from another lighting circuit. It still may not be the same light sircuit that feeds the upstairs lights.

 

[BabyT]

That's good. At least the neutral is borrowed from another lighting circuit. It still may not be the same light circuit that feeds the upstairs lights.

There's actually only one lighting circuit for my whole house. Very weird.