Lights wires

[MikeNW]

i have just installed new cieling lights in 3 bedrooms.

The first 2 bedrooms were easy 3 wires to connect pos/neg/earth.

The last bedroom though had 1 extra wire a BLUE ,what is this wire for? which pos/neg/earth should i put it in?

I think the blue wire may be going to my loftspace as there was a bulb fitted in up there and now it does not work-so could the blue be a live feed for the loftspace so should i fit it into the positive in the back bedroom?

ta

 

[Steve]

Only you can find out - go into the loft and see.

It would certainly be unconventional to only find ONE BLUE wire all on its own.

Oh and its not positive and negative. Its Alternating current - the voltage varies from about +320 to -320 a hundred times a second.

Line and Neutral please!

What colour is the wiring? red and black, or blue and brown?

 

[ban-all-sheds]

I think the blue wire may be going to my loftspace as there was a bulb fitted in up there and now it does not work-so could the blue be a live feed for the loftspace

Possibly.

As you didn't make a note of where it was in the old light before you removed it you're going to have to trace it and find out.

so should i fit it into the positive in the back bedroom?

Possibly.

Possibly not.

Connecting wires up on the basis of guessing or assuming what they are is not a good strategy - bad things can happen.

Follow the wire and find out where it goes and what it does.

 

[Space cat]

Where is the switch for that loft light? Is it part of a double? If it is then my guess is that the blue wire is the neutral return from the loft light.

But, as BAS says, guessing is not a good idea. Open up the light fitting in the loft (power off obviously) and look for the other end of that wire. If you find one that matches in size and colour, confirm it with an ohm-meter. You haven't finished yet. The light fitting will have at least one more wire in it which, more than likely, goes to the switch.

If, despite your best efforts, you can't find a matching end for that blue wire, DO NOT just connect it at random to live or neutral. Make your test connection through a light bulb instead. All you need is a pendant fitting, a filament bulb and some choc block. Try neutral first. If I'm right, the loft light and the test light will both come on dimly when you switch on. If I'm wrong, nothing nasty will happen.

 

[ColJack]

Oh and its not positive and negative. Its Alternating current - the voltage varies from about +320 to -320 a hundred times a second.

how do you know? for all you know the guy who put it in might have been a caravan nut and used a big 12Vdc power pack and some 12v downlighters everywhere..

it would be most usefull for emergency lighting as you could have a big relay and a car battery being charged somewhere...

 

[ban-all-sheds]

I think the OP might have mentioned that the cables were as thick as his arm...

 

[b13kal]

isnt this the case of shared neutrals

 

[b13kal]

Where is the switch for that loft light? Is it part of a double? If it is then my guess is that the blue wire is the neutral return from the loft light.

But, as BAS says, guessing is not a good idea. Open up the light fitting in the loft (power off obviously) and look for the other end of that wire. If you find one that matches in size and colour, confirm it with an ohm-meter. You haven't finished yet. The light fitting will have at least one more wire in it which, more than likely, goes to the switch.

If, despite your best efforts, you can't find a matching end for that blue wire, DO NOT just connect it at random to live or neutral. Make your test connection through a light bulb instead. All you need is a pendant fitting, a filament bulb and some choc block. Try neutral first. If I'm right, the loft light and the test light will both come on dimly when you switch on. If I'm wrong, nothing nasty will happen.

wouldnt it be best to call an electricaian?

 

[Space cat]

wouldnt it be best to call an electricaian?

That's certainly an option, but the OP will learn absolutely nothing that way. This is a DIY site and MikeNW went to the trouble of posting a question on it. My light bulb test should not be beyond the abilities of somebody who has successfully replaced two lights already.