Adding to a two way circuit

[Munroast]

I am wanting to add a lamp to a two way lighting circuit but it is not very practicable to add to the wires of the existing lamp within that circuit.

I am assuming all two way circuits are the same but if not I will briefly explain mine; In one of the switches the red wire is permanently live (feed) and on the other switch the red wire is only live when the lamp is on (load)

My job of adding to this circuit becomes very simple if I just tap into the red wire (load) that is only live when "ON" but if I do this what can I use as the neutral? - can I just tap the neutral and earth wires into another lighting circuit or for that matter any circuit within the property?

 

[ban-all-sheds]

I am assuming all two way circuits are the same

They aren't.

//www.diynot.com/wiki/Electrics:Two-way-lighting

In one of the switches the red wire is permanently live (feed) and on the other switch the red wire is only live when the lamp is on (load)

The colours mean nothing, from a functional POV - electricity can't tell what colour the insulation is, and doesn't care.

It's usual to use red in the 3C+E strapper as permanent live

but it will work just the same whatever colours are used.

can I just tap the neutral and earth wires into another lighting circuit or for that matter any circuit within the property?

No - you must not do that.

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

The only place you may get the neutral is from the same circuit.

 

[Munroast]

No - you must not do that.

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

The only place you may get the neutral is from the same circuit.

So it is acceptable to borrow a neutral from a circuit that would be in the same fused system?

For Instance; The garage lights are on the same fuse as the outdoor two way lights, so if I added to the outdoor two way circuit I could use the neutral and earth wires that service the garage lights ?

 

[ban-all-sheds]

Yes - that's not "borrowing" in the sense of a problematic "borrowed neutral". If they are on the same circuit from the CU it's fine.

 

[ban-all-sheds]

Apologies for this being an afterthought:

on the other switch the red wire is only live when the lamp is on

What test equipment did you use to establish that?

 

[Munroast]

Apologies for this being an afterthought:

on the other switch the red wire is only live when the lamp is on

What test equipment did you use to establish that?

The tip of my tongue

I used a volt meter and tested with and without the wire connected to the switch - I also tested L1 and L2 and ascertained they were working as expected.

I get the feeling you are going to say you never ever do that

 

[ban-all-sheds]

Use my tongue?

Not so far...

 

[Munroast]

Use my tongue?

Not so far...

Something else I noticed that I found a little odd whilst ascertaining what fuses related to what circuits. We have a couple of "double gang" switches operating lights that are served by two separate fuses - ie you could knock the fuse off for one circuit and still have a live wire in the switch!

 

[sparkwright]

Providing the two circuits are not 'bridged' together in anyway, it's perfectly normal for a 2 gang switch to contain two separate lighting circuits.

Most houses are like this at the hall/landing switch.

There are variations, where two lighting circuits share the same neutral, which can be problematic, but this isn't necessarily what you have.