Attic lighting not working - What's wrong with the wiring?

globalnic · May 22, 2016

Hi all, This may be one for the DIY forum, but I'm unable to post there, so I apologise if posting here is the wrong thing to do. I'm not a qualified electrician, but have taught myself how to changes light fixtures, switches, sockets etc - always after cutting all power from the mains and testing to make sure all connections are dead. We've recently bought a house (new build style, built 2006), and I've ventured into the attic after 1 week to see what's up there. There's a light fitted, which won't work. I've changed the bulb and checked the wiring of the ceiling rose (all looked fine), but no luck. Looking at the switch, it was wired differently to other switches I have seen. It appears to be a 1 gang 2 way switch with 2 T&E cables. Switches I have worked on before have been wired to work 1 way (even if on a 2 way switch), but have always just had the one T&E cable in to the box - this has two (I assume one for power in and one out to the light).

Live into COM, Neutral into L2, Earth twisted loosely with the earth from cable 2. Cable 2:Live into L1, Neutral into L2, Earth twisted loosely with the earth from cable 1. From the switch point of view: COM = 1 x live L1 = 1 x live L2 = 2 x neutral.

Aside from the fact I would have covered the earth with green and yellow and connected it to the earthing screw on the switch plate, it kinda makes sense to me: when the switch is on, the circuit connects the live wires taking power to the light, where the neutral wires are then connected back down through the switch and to cable 1. So what I want to clarify is:

1 - is my logic correct in how it should work?

2 - if so, should this still work with the neutral cables in L2 as shown in the pic, or should they be twisted together outside of the switch and covered separately in the box?

3 - Could this be changed to a 1-way switch, if the above is true, is my understanding correct that I could change this to a 1-way switch?

4 - Lastly, if the neutral cables aren't the issue can anyone suggest why it's not working? Sorry for the basic question. Trying to learn safely, so I thought better to ask people who know than to get fried by trial and error. Tried to give as much detail as poss, so sorry for the length as well!

Thanks for any help you can give.

Paul.M · May 23, 2016

Welcome to the forum. This needs an electrician to look at it for you.

If they are what you say, two neutrals terminated in the L2 (2 way) terminal, that would cause a fault current at the switch and trip the MCB when the switch is in off position (as you look at it). If the loft light is on a spur, I'm guessing the fuse has blown and the MCB reset so there is no noticeable difference in the rest of the house for the lights??? (we can only assume and guess at this stage).

An Electrician would take no time at all fixing this for you. Test equipment is needed and it will/should take less than an hour, small price to pay for it being safe and correct.

globalnic · May 23, 2016

Thanks for the response, and your guess at the problem. Helpful for my understanding of how things work and why.

You're right, no other effect on any lighting in the rest of the house - everything else seems to work as it should. I'll ask someone to come and have a look at it. I'm lucky enough that it's not a showstopper at the moment, we can get by with head torches if we need to go back up anytime soon.

davesparks · May 23, 2016

It is possible that it could actually work the way it is connected at the moment, and it is a method I have utilised in boiler wiring sometimes, but in this situation I wouldn't do it as the potential to start a fire of the switch moves a bit too slowly is pretty darned high!

telectrix · May 23, 2016

if that is an example of the installation (new in 2006 ) then i'd get a reputable electrician to do a full test/inspection. twisting bare earth wires like that is not acceptable in any way. hate to think what other horrors may be lurking.