Ceiling light permanently on - pops breaker when switched off?

[F54Mini]

Hi

So I wired in a new ceiling light and I was convinced I cabled it right be it seems not.

At the moment the bulb is on then the switch is in the OFF position and it I turn the switch on, it pops the breaker.

Old colours so red and black, no earth present. Light is Class 2

Three cables going to the old ceiling rose, assuming feed in, switch and feed out.

Three reds all in a choc block which I removed and stuck in a wago.

This leaves three blacks

Two have to be neutrals and one has to be the switched live. Two go to the neutral terminal on the new light and one goes to the live

How can I be in a situation where the bulb is on when the switch is OFF?

Surely if I had wired the blacks wrong, I would get no power at the light fitting at all? Like if the switched live is in with the neutral and the black going to the live is in fact a neutral, would I still get power?

I realise I’ve done something wrong but I can’t fathom how I have permanent power to the light with the switch in the OFF position using a black cable. I would expect no power or a trip when I switch the light on?

 

[ETAF]

post some images of switch and rose
do you have a multimeter ? and know how to use ?

 

[bernardgreen]

You have probably wired it like this

Neutral does not connect to the switch

 

[F54Mini]

post some images of switch and rose
do you have a multimeter ? and know how to use ?

I have a picture of the light fitting but not of the switch at the moment. Had to improvise with wagos as cabling was old.



I have a multimeter yes and have used it before but was a long time ago so would need to refresh memory.

 

[ETAF]

did you take a photo of the old wiring at all

Two have to be neutrals and one has to be the switched live.

Not quite sure as even if you used , the wrong black - which it appears - why the light would be on at all ?
depends i guess on whats going on at the switch

this is what you have - the switch colours could be changed for all reds and not 2 reds 1 black

Ceiling rose wiring (older cable colours)

www.ceilingrosewiring.co.uk

is the switch - just 1 gang and only controls that light

with all the wires disconnected form the connectors
with the meter you should be able once all disconnected - identify the power IN using the AC240V setting
then with power off
identify the switch cable - with the continutity tester - switching light switch on/off

 

[chivers67]

I think the cable supplying the light isn't the cable feeding the switch. It must be One of the other two cables - which is what Bernard implied.

 

[F54Mini]

To confirm, all three reds were in a choc block together before I started so they have to all be the lives.

Switch is one gang with a single two core cable going to it. Red in com, black in l1 as you would expect

 

[chivers67]

No - one of those Reds feeds the switch - if you've mixed up the one feeding the switch with a Feed that's why it's going pop when you short it out. You need to remove them from the Wago and find out which of those three wires is feeding the light switch preferably with a meter. Then the relevant switch live feeds the light. Have you got at least a voltstick?

 

[mcprinter]

The black on the right looks a bit 'manky'
Switched live should have a red marker on it. Is it the remnants of red insulating tape?

Post a pic of your multimeter if you are not sure how to use it.

 

[F54Mini]

Ok so used a multimeter on the black cables and seems two of them were showing 240v, one showed zero.

Of the two that showed 240v, one was only when the switch was on, the other showed regardless and this was the one I had into the fitting.

Stuck the other two blacks into a wago and the switched live into the fitting and it’s now working

Rather concerning that one of the neutrals is showing 240v though….

 

[chivers67]

The "Neutral" showing 240v should be when the Switch is turned on as it's the return from that - the switched live. That needs to have a small amount of Red sleeving on it to denote that

 

[F54Mini]

The "Neutral" showing 240v should be when the Switch is turned on as it's the return from that - the switched live. That needs to have a small amount of Red sleeving on it to denote that

No. two of the blacks are showing 240v

I expect one. The switched live. I have found this now, it’s plugged into the light and working fine

This leaves two more blacks which are both neutrals but one is showing 240v permanently. This was the one I originally had plugged into the fitting, hence why it was on without the switch being on.

Looking online it sounds like I have a neutral break somewhere which is causing 240v through the neutral circuit so I will have to find that. We have a shared neutral on the hallway/landing light setup so I wonder if it’s something to do with that

Blooming 1960s houses and their old electrics…

 

[Colin Brenton]

Don't forget, if a light downstream of the one you are working on has its switch turned on, the neutral coming back from it into the fitting you are working on will show as being live, if the live wire is connected.

If it all works when put back together I wouldn't be too worried about it.

 

[F54Mini]

Don't forget, if a light downstream of the one you are working on has its switch turned on, the neutral coming back from it into the fitting you are working on will show as being live, if the live wire is connected.

If it all works when put back together I wouldn't be too worried about it.

I wasn’t aware of that, perhaps that explains it then. It all worked fine when I connected it properly. I must have had the one testing 240v plugged into the fitting all along, hence why the light was on all the time and the switched live in the neutral block, hence why the breaker popped when I switched it on!

Appreciate all the replies, learned a few thing today.

 

[sparkwright]

Ordinarily, I would have been doing a simple continuity test with the power completely OFF.

On the continuity or resistance or ohms setting, with the power completely OFF, turn the light switch to the on position. Test between each corresponding red and black. Wait till you get continuity on one of the cables. If you do, turn the light switch to the off position. When you lose continuity, that is the switch cable.