Switch wire. 2 of 3 are live!

[Riki]

I am trying to wire back two ceilings lights in adjacent rooms but on trying to identify the "switch wire" in one of them I find 2 of the 3 black wires are live! How is this possible? Two should be neutral and one, the switch wire, live. In the other room it's OK, one live out of three. Help please.

 

[ianniann]

The only "neutral" that should be live is the switched live, and only when the switch is on which is a pretty simple way to identify it. It ought to be sleeved in red but often isn't.

The two "real" neutrals should be connected together, and to the lamp, so it is hard to see how one would be live and one not. A picture would help.

 

[endecotp]

How are you determining that a wire is "live" ?

 

[ericmark]

Black wire one is neutral.
Black wire two is neutral supply to next lamp, so with that lamp switched on it will be at 230 volt if not connected to black wire one.
Black wire three is switched line.

The problem is to work out which is which, I have tried many methods, however with AC there is an inductive and capacitive link which means logic does not seem to work, so only real way is power off, and connect meter buzzer cable to red, and other to black, and flick light switch until you find the switch cable, then clearly mark it up.

 

[EFLImpudence]

The only "neutral" that should be live is the switched live,

That is not a neutral.

Neutral is not a name for any black wire.

 

[securespark]

I concur with eric. An open neutral can show 230V.

 

[ban-all-sheds]

How are you determining that a wire is "live" ?

Maybe by using something which doesn't work?

But, but, but...

I am trying to wire back two ceilings lights

Before you removed them you could tell by looking which conductor was which without any doubt whatsoever.

Why did you decide to not make a note of which conductor was which so that you could reinstate them without any doubt whatsoever?

 

[Taylortwocities]

How are you determining that a wire is "live" ?

 

[Riki]

How are you determining that a wire is "live" ?

With a neon tester screwdriver.

 

[Riki]

Maybe by using something which doesn't work?

But, but, but...


Before you removed them you could tell by looking which conductor was which without any doubt whatsoever.

Why did you decide to not make a note of which conductor was which so that you could reinstate them without any doubt whatsoever?

I took photos of the wiring but somehow got it wrong (photo not clear which wire is which) because it doesn't work and I have tried all three permutations. One room is OK.

 

[Riki]

Black wire one is neutral.
Black wire two is neutral supply to next lamp, so with that lamp switched on it will be at 230 volt if not connected to black wire one.
Black wire three is switched line.

The problem is to work out which is which, I have tried many methods, however with AC there is an inductive and capacitive link which means logic does not seem to work, so only real way is power off, and connect meter buzzer cable to red, and other to black, and flick light switch until you find the switch cable, then clearly mark it up.

Thanks but only have neon tester screwdriver.

 

[Taylortwocities]

only have neon tester screwdriver.

Throw it away and get a two-probe voltage tester, or even one of the cheap multimeters.
You won't find much of use with a neon screwdriver driver. And they lie to you, and they won't tell you which wire is the neutral!

 

[ban-all-sheds]

I have tried all three permutations.

Do you really think that guesswork, trial and error, hoping to hit on the right combination by chance is a sensible way to be dealing with electrical wiring?

Basically you have to choose between Plan A and Plan B.

PLAN A:

• Learn how lighting circuits are wired.
  • //www.diynot.com/wiki/Electrics:Lighting
  • http://www.google.co.uk/search?q=uk+lighting+wiring+(basics+OR+101)
  • //www.diynot.com/wiki/Electrics:books
  • //www.diynot.com/wiki/Electrics:index
• Get a multimeter and learn how to use it.
• Identify which conductors are which at the switches and the light positions.
• Check for circuit continuity, switches working etc.
• Connect everything up properly.

PLAN B:

• Get an electrician.

There are some irresponsible people here who will tell you that there is a Plan C, which is to start trying different things without really knowing what's going on, hoping to get it working by luck, or by blindly following instructions to put-this-wire-in-that-hole without any idea as to why. Please don't listen to them - you must know what, and truly understand what, you are doing.

Electrical-installation-by-guesswork is a foolish idea.

There is no Plan C for anybody sensible.

 

[Riki]

Throw it away and get a two-probe voltage tester, or even one of the cheap multimeters.
You won't find much of use with a neon screwdriver driver. And they lie to you, and they won't tell you which wire is the neutral!

Determined the switched wire, rechecked the connections, everything appears perfect and yet the light in one of the rooms does not work together with other lights in the house. I am at a loss...

 

[Riki]

Do you really think that guesswork, trial and error, hoping to hit on the right combination by chance is a sensible way to be dealing with electrical wiring?

Basically you have to choose between Plan A and Plan B.

PLAN A:

• Learn how lighting circuits are wired.
  • //www.diynot.com/wiki/Electrics:Lighting
  • http://www.google.co.uk/search?q=uk+lighting+wiring+(basics+OR+101)
  • //www.diynot.com/wiki/Electrics:books
  • //www.diynot.com/wiki/Electrics:index
• Get a multimeter and learn how to use it.
• Identify which conductors are which at the switches and the light positions.
• Check for circuit continuity, switches working etc.
• Connect everything up properly.

PLAN B:

• Get an electrician.

There are some irresponsible people here who will tell you that there is a Plan C, which is to start trying different things without really knowing what's going on, hoping to get it working by luck, or by blindly following instructions to put-this-wire-in-that-hole without any idea as to why. Please don't listen to them - you must know what, and truly understand what, you are doing.

Electrical-installation-by-guesswork is a foolish idea.

There is no Plan C for anybody sensible.

Done Plan A but still no joy. The light in room No. 1 is fine but not in No. 2 which will not light together with other lights in the house. Checked and rechecked the wiring several times.