Lighting problem - can someone advise please

[mattyninegrand]

Hi

A light switch in my sitting room stopped working, looked at the switch and I have two red wires and an earth, I was expecting 240v on the live and 0v on the switch live but I am getting approx 150v on both even with the switch disconnected. I traced the wire and believe its linked to the light in the kitchen so checked the switch in there, this time there is also a neutral in the switch and I am getting 150v on the live and 80v on the live switch even with the light off but the light still works.

Any ideas please?

 

[wingcoax]

How many cores connected to the kitchen switch? It is likely the "neutral" is the switch live return to the light, it should have a red/brown sleeve.

 

[mattyninegrand]

The kitchen switch has 2 red and 1 black and an earth, is it possible it has a neutral because there is another switch for the kitchen light across the other side of the kitchen?

 

[wingcoax]

It sounds like a two way circuit. Neutrals are normally linked at the light fitting.

 

[mattyninegrand]

Ah right ok, so any ideas what could be causing the sitting room light to have 150v on both live and switch live?

 

[ban-all-sheds]

Induced voltage - I bet if you used a moving coil voltmeter you'd not see a voltage.

If you connect the two reds in the sitting room switch together does the light come on?

If so you know that the switch is knackered.

 

[mattyninegrand]

Induced voltage - I bet if you used a moving coil voltmeter you'd not see a voltage.

If you connect the two reds in the sitting room switch together does the light come on?

If so you know that the switch is knackered.

Tried another working switch on it and still nothing, the light at the other end of the sitting room has two red wires and that seems to be fine as i am getting 240V and 0V and then 240v on both wires when switched on.

 

[Taylortwocities]

Between which two points are you measuring these voltages?

 

[mattyninegrand]

Between which two points are you measuring these voltages?

Live to ground and switch live to ground

 

[mattyninegrand]

Right so i've cleared my head and now understand how the lighting circuit works, live to switch from switch to bulb out of bulb throught neutral back to main board. A continuous live loop and each live spurred off this loop and a continuous neutral loop with all neutrals connected to this loop.

So, if i have a break in a neutral a live feed goes to the bulb, out of the bulb via neutral and connects to neutral loop but because of the break it cant return to the main board so current continues onto next spur off (next light in the circuit), thus giving me voltage on both live and neutral even when light turned off.

This is basic, same as car dc - battery live to switch, to load, to battery earth.

So question I have is - why is there a neutral in the kitchen switch but not in the sitting room switch? what would this achieve and it is a neutral in the switch and not a switch live as I have a switch live in there asell.

 

[mattyninegrand]

As I have another light switch across the other side of the kitchen that controls the same light is it possible what I am calling the neutral wire in the switch actually a live feed for the other switch in the kitchen?

 

[Taylortwocities]

How many cores connected to the kitchen switch? It is likely the "neutral" is the switch live return to the light, it should have a red/brown sleeve.

As stated before. It is NOT a neutral it is just a wire that is coloured blue, or black. The function of it depends on the wiring. It is probably a conductor that becomes live under certain circumstances.

Have alook at the WIKI's excellent lighting wiring diagrams and compare those with the wiring at your house. It may then make some sense.

//www.diynot.com/wiki/electrics:lighting

 

[mattyninegrand]

thanks, something to get my teeth into but i'll make sure i turn the main supply off first