Two gang switch wiring probs!! Help.

[Mattayscough]

Yep. They are all firmly screwed into the back box. I was just a little surprised to see them as I was expecting the switch cable to consist only of a single 2 core and earth cable with the black and red fed into switch with earth to the back box. This is the way that all the books that I have show it done.

Why would someone use two cables rather than one? Is it ok to use the same configeration or should I replace with one 2 core and earth cable and label at the junction box the 'live' black cable that returns from the switch?

 

[Spark123]

Yep. They are all firmly screwed into the back box.

Is the neutral conductor accessable at all to the outside of the back box, i.e. can you come into contact with the metal of the neutral conductor?

Why would someone use two cables rather than one? Is it ok to use the same configeration or should I replace with one 2 core and earth cable and label at the junction box the 'live' black cable that returns from the switch?

It sounds fine as it is (subject to above), what it sounds like they have done is pick up a live, neutral and earth feed from the lighting circuit(?), run this feed to the switch and jointed the neutrals at the switch (and jointed the earths), so leaving the switch on the other cable is switched live, neutral and earth which goes to the light.

 

[ban-all-sheds]

The point about "correct electrical terms" is not pedantry, or electricians showing off their depth of knowledge, it's because getting them right, particularly when it comes to the issue of whether a wire is live or neutral, is of enormous importance - possibly of life/death level of importance.

You've been "assuming" things about your wiring, such as where the circuit loops in, and what the functions of the conductors are based on an incomplete understanding of the different ways that lighting circuits can be wired. Assumptions like that can be very dangerous.

For example, if you decided, on the basis of your assumption that the black cores were unused, to replace your backbox with a metal one and replicate the connections you have now, then if your installation has no RCD everything would carry on working fine, but a dodgy earth could result in somebody being killed.

Why would someone use two cables rather than one?

One reason could be because the lighting circuit loops in at the switches. Another reason could be that for this particular light a L&N feed was taken from the lighting circuit, to the switch, to then supply L&N to the light.

Is it ok to use the same configeration or should I replace with one 2 core and earth cable and label at the junction box the 'live' black cable that returns from the switch?

You cannot do that unless you establish beyond doubt that the black wires are not neutrals. If they are, then what you propose will stop the light from working, and if you pick the wrong cable to put inti the switch you'll get a big bang, a blown/tripped fuse/MCB and probably a wrecked switch.

 

[Steve]

I am swapping over to a new switch . . . . <irrelevant stuff>

you are fitting a new switch. Why did you have to examine the wiring? the light worked before, yes? so why not just connect the switch back up as before and have done with it?

 

[Mattayscough]

I am moving the switch by about 18 inches and going from a surface mounted box to a flush plate type. Also the face plate is brass. Does this cause potential problems with the neutrals being in the box? I am guessing that this is not good news??

 

[ban-all-sheds]

1) You must be sure that the lighting circuit earth is continuous and provides a good connection back to the earth terminal in the CU.

2) You must not join the neutrals (if that is what they are) by connecting them to an earth terminal in the box - you must use a piece of choc-block instead.

3) Stop guessing!

 

[Spark123]

Also when moving a switch, any concealed cables should be in permitted routes etc:
http://www.niceic.org.uk/downloads/C5-43.pdf
http://www.niceic.org.uk/downloads/concealedcables.pdf

 

[Mattayscough]

ok ban-all-shed. I understand the point about getting it right. The other users just seem to be able to advise without sounding school teacherish.

Spark123 it appears that the lighting circuit might be looping in at the switch (is that what it's called?) because each switch has 2 x cables. One is a standard 2 core and earth and the other has a yellow wire?

My manuals only show lighting circuits where there is one cable to a one gang switch.

 

[Qedelec]

Mattay
The way your lighting circuit is wired is becoming increasingly popular. I suspect you're in a fairly new house.
They frequently take the feed (live, neutral & earth) to the switch, connecting the neutrals together in an insulated terminal. This makes it easier for adding any additional lights, you can add a 2 gang switch and take the feed via the dry line cavity to the new light.

Hope this makes sense to you.

 

[Mattayscough]

Quedelec.

Thanks for that. I have a Victorian house but the wiring is fairly new and it has all been surface mounted (mmm nice!).

Do you have any links to wiring diagrams that illustrate this kind of wiring arrangement? It's just a bit disconcerting because I only have diagrams of junction book and loop-in lighting circuits.

Does anyone have any diagrams of this sort of circuit or even a name so that I can search Google?

Thanks again.

 

[Steve]

it's an easy system to understand. One cable is permenant live and neutral. The other cable is Switched live and neutral. Advantage is that it makes it easier to add lights on, without having to take ceilings down and interfere with crowded ceiling roses etc. Also a lot simpler to change light fittings from plain pendant drops.

 

[Mattayscough]

Easy if you've got experience with this sort of thing. All I have done before if changed switches and celing roses on 'normal' junction box and loop-in circuits.

If anyone has a diagram of an example of how these circuits run or even the name of this kind of circuit so that I can look it up in a electric manual I would be very grateful.

Ta muchly.

 

[Steve]

one simple diagram, think it gets the point across. . . .

this one uses 2 live feeds, one comes from the previous switch, the other goes on to the next switch.

 

[ban-all-sheds]

And with only two cables, it means that your switch is the last one on the circuit.

OR - it's the only one like this because someone wanted a light that was nowhere near where the lighting circuit ran, and the easiest thing to do was to take permanent live and neutral from a ceiling rose or JB to the switch and then off to the light.

ALSO - everyone please note - we still do not know for sure that these blacks are functional neutrals, nor will we unless Mattayscough does some more investigation and testing...