3 lights controlled by two cables ? How ?

[MrTeeny]

I'm replacing some wiring because of decorating and replacing lights. Thought I may as well replace the old cable whilst I've access to everything.

At the moment there are four lights - main one, middle of the room controlled by the top switch then two wall lights controlled by one switch and one wall light controlled by the other switch.

Can someone explain how the wiring on the wall lights has been done to control two separate lights from the one cable ? There's no earth on the switch cables so it all needs replacing and I'll most likely channel the wall and stick another cable run down the wall so there's 3 switch cables to make it easier for me to understand my wiring but was wondering how the circuit manages to run two lights from one 2 core cable.

The red has been been attached to the common connections

Thanks

 

[plugwash]

it looks like the cable going to the top switch carries a permanent live and a switched live to the main light. The permanent live is then brough to the bottom switches by short link wires. The second cable then carries both switched lives.

Be warned, when you see setups like this it is very common for the neutral to be "borrowed" from a different circuit. This is a bad thing from a safety point of view and can cause problems later if only one of the circuits is placed on a RCD or both circuits are put on different RCDs.

 

[electronicsuk]

The switch doesn't run two lights through one two core cable, per se. It uses 2 * 2 core cables (in all 4 cores) to control three lights. One core is a permanent live feed which is looped through to all 3 switches, the three remaining cables being switched live returns.

The whole lot will likely terminate in a junction box somewhere in the ceiling above, where the supply cables run out to the light fittings and pick up their neutral and earth.

 

[MrTeeny]

Thanks that makes a lot more sense to me now, electronicsuk, having one live and three switched lives.

It's all cobbled together in a junction box where the feeds to the lights get picked up (they're just 2 core no earth cables so need replacing). Is that quite normal then and quite safe for me to replicate the circuit using 2 * 2 core and earth cables again having a permanent live ?

Pugwash can you explain what you mean about a borrowed neutral ? The junction box has a feed going in supplying the 4 lights and then the feed carries on to another part of the lighting circuit so I assume it hasn't been borrowed.

 

[plugwash]

It's all cobbled together in a junction box where the feeds to the lights get picked up (they're just 2 core no earth cables so need replacing). Is that quite normal then and quite safe for me to replicate the circuit using 2 * 2 core and earth cables again having a permanent live ?

Yes that is fine, make sure any existing earth wires you connect to are really earthed.

Pugwash can you explain what you mean about a borrowed neutral ?

A borrowed neutral is where the neutral for an appliance is taken from a different circuit to the live. It is unfortunately quite common in wall lighting setups for a diyer or cowboy to take the live from the lightswitch and the neutral from a nearby socket.

The junction box has a feed going in supplying the 4 lights and then the feed carries on to another part of the lighting circuit so I assume it hasn't been borrowed.

correct

 

[MrTeeny]

Thanks , is it quite usual to use 2 core cable without an earth ? or was that just cos the wires are old before regs changed etc.

Hopefully I'll be able to fit the new cables down the existing channel as I've had probelms before trying to fit a 3 core and earth 1.5mm for 2 way switching down a similar channel before. Don't suppose you have any tips for getting the cable through

 

[plugwash]

From what I can gather 2 core cable without an earth used to be common for lighting circuits back in the 1960s, then the regs changed a bit to basically disallow cables without earths in domestic fixed wiring.

 

[RF Lighting]

Will the junction box remain accessible?


Personally, I don't like to use the junction box method for lighting.

 

[MrTeeny]

Will the junction box remain accessible?

If under the floorboards in the upstairs hall is considered accessable then yes

What other methods could I use ? I'd assume a junction box would be the best way to go otherwise they'd be wires all over the place with four lights to switch and feed. Open to any other suggestions.