Lighting Circuit Problems

[Mr. Fantastic]

Hi, I'm new, know very little, and I need help. I've had a quick look through the FAQ and checked Google for any previous answers but couldn't find anything, so here goes...

I have broken my electricity.

In a foolish and now aborted attempt to fit a new (flush) light to my landing I switched off the light circuits at the consumer unit, removed the existing ceiling rose, disconnected all the wires and...changed my mind. It didn't have the right connections, it wouldn't fit properly and, worst of all, it looked crap.

So, I reconnect all the wires, switch everything back on and...nothing happens. Upstairs lights work fine, sockets work fine but no lights work in the landing, stairs, bathroom or kitchen. The light in the lounge work, I'd guess they're connected to the upstairs circuit for some reason.

Anyway, switch everything back off, check connections. All are definitely in the right place and properly fitted. Go to consumer unit to try again...oh...the main switch has tripped. Switch it back on, switch light circuits back on, same result - everything works except the lights on the downstairs circuit.

Any clues apart from 'get a man in'? I thought the mcb for the downstairs lights may have gone in the consumer unit, but as I can switch it on and off I would guess not. Anything useful appreciated, and many thanks.

[Gary Cavie]

Assuming a fairly standard setup, your should have three cables coming into the ceiling rose. (3 reds, 3 blacks, and 3 earths). Two of the cables will be the feed in and out, and one will go down to the switch. On the switch cable, the black will be a switched live, and NOT a neutral.

Ideally, you need a meter to identify the switch cable (check for continuity between black & red with the switch on, and no continuity with it off (Obviously, this must be done with the power off!) Once you have identified the switch cable, push it to one side for now. Connect the other two cables with the reds to the three terminals in the central block of the ceiling rose, the two blacks to the block to the side which has three terminals, and the earths under the earth screw. The switch cable has it's red connected to the other two that you have just put into the central block, and the black, with a bit of red sleeving/tape, to the block which only has two terminals. Finally, the lamp flex connects with the brown to the black/red sleeved wire from the switch, and the blue to the two other blacks.

When you say that the main switch has tripped, do you mean an RCD covering the whole house, all circuits etc? This could well have happened with a stray touch to earth from a neutral, whilst you were moving wires. If you mean the MCB for the lights, this could be due to having the switch cable connected stright across the supply, thereby shorting it out when you operate the switch.

There is a picture showing what I have failed to clearly describe at the following link:

this helps

Gary

[Gary Cavie]

Should really clarify the above - to identify the switch cable, you are looking for continuity of probably less than one ohm between red & black

- if you look towards the rest of the lighting circuit, and have a light switch on on that part, you will see continuity through the bulb, which will be in the order of tens of ohms. Either make sure that the other switches are off, or remove the other bulbs to be certain.

[<me9]

Just operate the switch. It should change from 1megohm. That would be conclusive.

[Gary Cavie]

D'OH - it must be getting late! Good point, well made!

[Mr. Fantastic]

Hmm...I haven't tested it yet but there is a black wire with about an inch of red sleeving, I'm assuming that's the switch. If so, everything is connected exactly as you describe.

The RCD tripped, thanks for the explanation as to why it might have happened, that seems a likely possibility.

I haven't had time to look into it today (I'm just going to sit down to dinner!) but I have noticed that, contrary to my first opinion, the lounge light is actually on the downstairs circuit, and that works fine. So, could I assume that this is the first light on the circuit and there must be a break somewhere between that and the landing light which is causing the rest to fail?

Thanks for the help, it's much appreciated.

[Gary Cavie]

OK, Assuming that it hasn't been incorrectly labelled in the past, the next thing to check is if power is actually getting into the rose. Make sure that the bulb in the lamp is good, and move the brown wire from the lamp flex into the block containing the three reds, then turn the power back on. If the bulb comes on permanently, then you know that the MCB and wiring up to that light fitting is good. Alternatively, if you have a meter just check for 240v across the reds and neutrals.

If there is no power there, then it looks likely that either a wire has broken from the moving around, or one of them isn't connected properly, or you have a problem back at the board. Do be careful when checking these though, as if a neutral has gone open circuit, you could still have mains voltage appearing on the neutral side of the circuit, with apparently no power! Make sure that the MCB is off first...

No problem, keep me posted how you're getting on.

Gary

[Mr. Fantastic]

Not a sausage.

Bingo!

I checked the ceiling rose in the lounge (which was still working and so presumably the first light in the downstairs circuit before leading to the landing) and the earths had been disconnected. After reconnecting them everything else to functioned correctly.

Thanks for your help, Gary. It was very much appreciated!

[Gary Cavie]

Wo, wo, wo - hang on a minute! The earths being disconnected shouldn't make any difference to a healthy circuit functioning! Please tell me that you meant the neutrals! If not, then you have another, more serious problem there. Can you just confirm for me whether it was the earths or neutrals?

[Mr. Fantastic]

Whoops, forgive my slippery fingers there. The earths and some of the lives had been disconnected. I'm pretty sure the neutrals hadn't moved, though.

[Gary Cavie]

OK, I'll let you off! It should be the lives which made the difference, not the earths. If _they_ were the difference between working and not, we have a whole different set of problems to look at!

Glad it's all OK now

Gary