Wiring in a light fitting with 2 switches

[Robbie1980uk]

Hi all,

I am changing a light fitting in my hall. This light is controlled by a switch at the top of the stairs and another switch at the bottom.

Coming from the ceiling I have 2 mains cables coming out (one set of L, N, E and another set of L, N, E).

School boy error- I didn't note what the where the wiring went on the old light fitting!

On the new light fitting I am putting up, it only has one set for L, N, E wires.

Any help would be appreciated...!

 

[Robbie1980uk]

Do I just pair all the L, N and E's together?

 

[Megaohm7]

Not as simple as that I'm afraid. You have a line and neutral coming in and the other cable will be to your switch. The only way for you to tell which is which is to firstly isolate that circuit and to test for continuity from the switch controlling that light and to the cables coming out of the ceiling position. If you're not sure or feel confident to do this then you'll be best to get a qualified spark in. what area do you live? A member that lives near might arrange with you to come out and sort it for you.

 

[Robbie1980uk]

Live in Gourock in Scotland.

So I should connect the lives together (in a loop) like this:

http://www.diy.com/diy/jsp/content/knowledge/images/how_to/fix_ceiling_light/3.gif

?

I can check which one is which. I have a DVM about somewhere.

 

[sellers]

yes thats how it should be from how you describe. you need to test which blue is the switch wire, if you mix up the 2 blues the fitting will still work but with it will not have the correct polarity.

 

[Megaohm7]

That's how it's done. As long as you can safely identify what your switch wire is then you'd have cracked it.

 

[NozSpark]

Live in Gourock in Scotland. So I should connect the lives together (in a loop) like this:

http://www.diy.com/diy/jsp/content/knowledge/images/how_to/fix_ceiling_light/3.gif

?

I can check which one is which. I have a DVM about somewhere.

It's easy if you have a DMM.

Turn the circuit off,

Set your meter to the ohms range,

Connect one lead to a brown and the other to it's blue,

With the switch "on" you should have as near as 0ohms and "off" you should get infinate ohms. Try both pairs!

Which ever pair gives the readings as stated above, mark the blue with some brown sleeving (or tape if you must)

And then connect it up as in your picture (blue marked brown as switched live)

 

[Robbie1980uk]

Even if I have the neutrals round the wrong way- having a reversed polarity- would this be bad? Sure, not ideal, but would it be unsafe?

 

[Robbie1980uk]

(thanks for all your help by the way)

 

[NozSpark]

But you won't have the neutrals the wrong way around,

You'll have the switched live and neutral the wrong way around.

And yes it does matter, especially if the lamp holder is a screw in type

 

[sellers]

Simple way to check after its all connected is to check for 230v across switch live and earth when the lights on. Bear in mind you will be opening the ceiling rose/light while live so only do it if you feel confident and competent.

 

[ProDave]

deleted

(miss read a previous post and the correct advice had already been given)

 

[Robbie1980uk]

But you won't have the neutrals the wrong way around,You'll have the switched live and neutral the wrong way around.

And yes it does matter, especially if the lamp holder is a screw in type

How does it matter, give me specifics lol makes me understand it better u c.

 

[NozSpark]

Ok then,

1 It's good working practice to correctly identify and terminate cables (also in the regulations), it also makes it easier for the next person coming along.

2 ES lampholders need to have the correct polarity because unlike a BC lampholder it uses the threaded part as the neutral connection, get it the wrong way around and the threaded part becomes live. If you then toch it whilst removing a lamp you could get a shock

 

[Megaohm7]

How does it matter, give me specifics lol makes me understand it better u c.

It's all down to polarity. The Line/live should be at the center terminal for a screw type lamp rather than the other way round as you can still possibly touch the threaded part which should have the neutral connected to it when the lamp is in its holder. There is a screw type fitting that is exception to the rule I can't think of the type number just now but hope this makes a little sense to you.

 

[Robbie1980uk]

Thanks guys that makes sense to me.