ceiling wiring

[Chris S]

Hi
just looking at the wiring in our new house. The bathroom light fitting wiring currently features 2 lives tied together as well as 2 earths tied together. Neither combination is used with the actual light fitting. Can sort of understand this tying together in a "1-way" sense but am intrigued why they used the 2 neutrals for hooking up to the light fitting?

 

[Space cat]

-- am intrigued why they used the 2 neutrals for hooking up to the light fitting?

One of those neutrals is a switched live coming back from the light switch. Rather than make special 2-core cable with a different colour for switched live, it's standard practice to just use the same stuff. It's also good practice to mark a switched live wire with a piece of sleeving (red or brown) to distinguish it from true neutral but it isn't always done.

 

[riveralt]

Hi
just looking at the wiring in our new house. The bathroom light fitting wiring currently features 2 lives tied together as well as 2 earths tied together. Neither combination is used with the actual light fitting. Can sort of understand this tying together in a "1-way" sense but am intrigued why they used the 2 neutrals for hooking up to the light fitting?

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

 

[EFLImpudence]

A wire can be used for whatever you want - they don't know what colour they are.

One of the reds goes to the switch and the black is a switched live, not a neutral.
It will go bang if you connect it to neutral.

P.S. A 'neutral' is the wire used to complete the circuit from a load back to the supply source.

 

[sparkwright]

They are not both neutrals.

One is a neutral.
The other, which should have a red or brown sleeve over it to indicate it is live, is the switched live.

You see, the two lives not connected to the light are permanent lives. One wire is the permanent live feed, which is joined here to feed the switch. Then at the switch another wire comes back, known as the switched live, to the light.

It's much easy to understand if the 'switched live' is red or brown, or sleeved with a short piece of red or brown sleeving.

If the earths are not connected to the light then hopefully it's a plastic class 2 fitting which doesn't require an earth, though the earths must still be joined together.

 

[PrenticeBoyofDerry]

It may not be two neutrals, just because colour cores are same don't assume they serve the same purpose.
Your two lives are the loop, this will supply a live to the switch and a return switch wire could be core coloured as the neutral but is in fact the live, to the live side of the lamp and should be marked up as so for identification of the cable.
The other cable will be the neutral to neutral side of lamp.
This is seen, because twin and earth with core colours for live and neutral are often used for switch drops, but should be identified as live, with PVC sleeving.

 

[vibrobullit407]

The way the light is wired is called the looped in method. One of the twin and earth cable comes from another light fitting. This cable brings the line and neutral to the fitting. The other cable goes to the switch. So by connecting the red from the loop to the red from switch means that you will have power at the switch. This inturn switches to the black core on the switch making this your switch line. This means as spacecat states that one of the blacks to the light is your switch line and the other one is your neutral. If you have a look on the wiki you will be able to see a wiring diagram of this method.

 

[ban-all-sheds]

am intrigued why they used the 2 neutrals for hooking up to the light fitting?

That you think the light could work if all it had connected to it was 2 neutrals shows that you don't have much of a grasp of basic electrical circuits.

If you plan to do any electrical work in your new house then you must acquire a sound grasp, as doing electrical work without truly understanding what's going on is a Very Bad Idea.

• http://www.google.co.uk/search?q=electrical+circuits+101
  
  
• http://www.google.co.uk/search?q=multimeter+101
  
  
• http://kevinboone.net/electricity.html
  
  
• http://web.archive.org/web/20080213151445/http://www.kevinboone.com/domesticinstallations.html
  
  
• //www.diynot.com/wiki/electrics:books
  
  
• //www.diynot.com/wiki/electrics