Strange wiring? Live wire linked to com on second switch

[kingandy2nd]

Hello,

I was looking to change a 2 gang 2 way switch for a newer switch.

When I took off the old switch the wiring wasn't what I expected. The switch on the right hand side from the front (on the left in the photo) is a 2 way switch. The other switch on the right is a 1 way circuit to an outside light.

The 1 way circuit switch has a small wire from the live connected to the com on the 2 way circuit (red wire in the top right of the photo). The switch has a single core wire heading to the light.

Unfortunately I'm not able to follow the wiring all the way to the light as it goes into the cavity wall and runs for several meters before coming out on the exterior.

I've not seen wiring like this before, is it normal? Any ideas how the exterior light gets its earth and neutral feeds assuming this single core wire takes the live supply to the light?

(Ps I know the switch is upside down from the switch brand, that's how it's been wired)

Thanks
Andy

View media item 53630

 

[EFLImpudence]

The 1 way circuit switch has a small wire from the live connected to the com on the 2 way circuit (red wire in the top right of the photo).

Other way round.

The switch has a single core wire heading to the light.

That'll be the switched live.

I've not seen wiring like this before, is it normal?

Yes, perfectly normal.

Any ideas how the exterior light gets its earth and neutral feeds assuming this single core wire takes the live supply to the light?

Probably from the light fitting which is operated by the two-way.

 

[securespark]

Not easy to confirm from the piccy: is that rubber cable?

Do you have earth wires?

 

[ericmark]

The use of twin rather than triple core cables between two way switches has now been discontinued due to both mains hum produced on audio equipment and the possibility of shared neutrals.

I would guess today it could also cause problems with broad band but years ago this was quite common.

If the two way lighting is the stairs then I would be worried about shared neutrals but unless you are having problems with mains hum on radios, TV etc then I would not really worry about it.

However it is something to remember and if you do find problems likely it will only exist in one of the four positions of the two switches so often people are unable to work out where or why it is happening.

Because in one position the line and neutral cables are not running together the impedance of the cable is not matched so it transmits 50Hz around the house.

It is however a very minor problem and nothing to worry about.

 

[kingandy2nd]

Thanks for yoru input guys.

EFL - yes sorry, I've got my live and com the wrong way round.

I still don't understand though how this works. What is the other end of the neutral and earth coming from the exterior light connected to?

I don't see what purpose running a single live cable from the switch has over the conventional way of wiring it...especially considering there's another switch wired normally next to it?

Securespark - I'm not sure what the cable is made of, but it is has a larger sleeve than a normal 1mm wire. The box is earthed by the circuit on the other switch (the 2 way) but I can't see any other earth. (I've not taken the exterior light off the wall to look from that side).

Ericmark - this doesn't appear to be a twin cable set up. It's just one single core cable running from the switch to the light.

Cheers

 

[EFLImpudence]

NO neutrals at the switch.

The wire to the light is live when switched on.

The wires can be whatever we want them to be. They do not know what colour they are.

 

[securespark]

Re the earth. I've seen loads of 2 way switches wired similarly where you have just a single core at either end with a twin running in between the switches. The twin & earth is not connected to earth, only to the boxes for each switch!

But if you can't see an earth wire at one of the switches that suggests there may not be earth continuity to more parts of the circuit.

 

[kingandy2nd]

Thanks guys.

Right, I've checked at the exterior light end of the circuit and there is an earth cable coming from it. The switch end of this circuit isn't earthed.

If this is an accepted way of wiring, I will just replicate it with the new switch.

Cheers
Andy

 

[ban-all-sheds]

I've checked at the exterior light end of the circuit and there is an earth cable coming from it.

No, there's an earth going to it.

Where does that earth originate?

 

[Lectrician]

You will probably find the outside light has a neutral which is also a single (double insulated) core. This (and the earth) will likely run back to the hallway pendent.

 

[kingandy2nd]

Ban-all - afraid the wires disappear into the cavity wall and only reappear above the fuse box in a gaggle of wires.

Lectrician - you are correc that the wires from the exterior light are as you described.


Thanks again to all for your help. As you've confirmed that this set up is ok, I'll just wire up the new switch with the existing wire config