How to find a lighting fault?

[Iain741]

Hi all,

I'm looking for some pointers in finding a fault in a ceiling light at the top of my stairs. There are 2 switches + an intermediate switch (bottom of the stairs, top of the stairs & hallway). I tested with a voltmeter at all switches and the light itself and there's no power.

Any advice where to start? Fuses on the consumer unit are all fine. The switch at the top of the stairs has 2 cores connected in a terminal block, would that be where the power should be fed into the circuit? Should i just be trying to trace that cable to check the source?

It's the only light that doesn't work upstairs. Just moved in the house a couple of months ago and it's never worked.

Cheers

 

[jj4091]

Electrics:Intermediate

www.diynot.com

 

[Taylortwocities]

The switch at the top of the stairs has 2 cores connected in a terminal block, would that be where the power should be fed into the circuit?

Normally the power feed is provided at the light fitting.

Lets see photos of the wiring at all three switches and at the light fitting itself.
When you say

I tested with a voltmeter at all switches and the light itself and there's no power.

Between which points did you test?

EDIT. I see this sort of thing a lot. Person sells house and swop their fancy switches for cheapo ones before moving out. Connection not done correctly and, as a result, something doesnt work. That may not be the case, but could be....

 

[ericmark]

A standard ceiling rose has three sets of terminals plus an earth clamp. Out of interest I held my own tester at ceiling rose with switch off, and it beeped and the red LED lit to show power at the ceiling rose without removing the ceiling rose cover, same with switch, as to if cheaper testers will can't say.

But be it a neon screwdriver or a full blown multi meter as shown, you do need a tester, so I will start with neon screwdriver, which should show centre block of three as being live, with switch on or off, and with switch on the block of two should show live, but a neon screwdriver can not test the neutral, however if you know you have a live, then a wired multi meter will then show if you have a neutral.

However step one is to find out what testers you have, and what the ceiling rose looks like, and once we know that we may ask to see inside the switch, as it stands we don't even know if you have a ceiling rose, my landing light the ceiling rose has gone. All the wires are inside the fitting, including a smart relay, so give us a clue as to what you have.

 

[ericmark]

The ceiling rose should look some thing like this
L is line to lamp, LL is line loop, N is neutral and E is earth. Even with switch off LL should be live, what the switch does is connect LL to L, This is the basic wiring for three switches the right hand of the three loops is what goes from ceiling rose to switches, i.e. just two wires, the loops show what wires are in each cable.

So with power off, a link L to LL then turn power back on, and lights should work, switches will do nothing, but it proves the light. Once sure light is OK then we go further, but prove the light works first.

***Moderators note*** this post has been edited and several posts have been removed from this thread due to unnecessary and unwanted pedantry from the village idiot causing an off topic discussion.

 

[denso13]

There's a guy here, https://electricianforum.co.uk/threads/solar-system-review.54835/page-2#post-527404, who seems to agree with Winston. Word for word in many of his posts strangely...

 

[opps]

Hi all,

I'm looking for some pointers in finding a fault in a ceiling light at the top of my stairs. There are 2 switches + an intermediate switch (bottom of the stairs, top of the stairs & hallway). I tested with a voltmeter at all switches and the light itself and there's no power.

Any advice where to start? Fuses on the consumer unit are all fine. The switch at the top of the stairs has 2 cores connected in a terminal block, would that be where the power should be fed into the circuit? Should i just be trying to trace that cable to check the source?

It's the only light that doesn't work upstairs. Just moved in the house a couple of months ago and it's never worked.

Cheers

December last year, I decorated a house. The customer's electrician came in to fit new flush light switches. I turned up at 6.30 the next morning. The lights downstairs worked but the light at the top stair well would no longer work.

The electrician were now on holiday and I needed to see what I was doing.

I resorted to having to use long lengths of alarm cable running from the ceiling rose (via the probes on multimeter) to the two light switches to identify which cable performs which function. The power was turned off and I used the continuity setting on my cheap multimeter. The electricians had accidently swapped over L1 and a COM.

Bizarrely, they didn't notice that any of the lights upstairs no longer worked. I traced that fault to a faceplate fixing screw running through the live and bridging the metal back box. I used some heat shrink sleeving to repair the cable.

 

[Iain741]

Here’s some photos of the back of the switches. I’ll open up the ceiling rose again and take photo, but it was the same as the diagram attached that I found online.



I was testing with a decent enough Fluke. I’m confusing myself where I tested from now…which points should I test across? Testing across COM and L1 when the switch is on, I read 135VAC. Across COM and L2 when the switch is off, I read 205VAC.

Cheers

 

[opps]

Here’s some photos of the back of the switches. I’ll open up the ceiling rose again and take photo, but it was the same as the diagram attached that I found online.



I was testing with a decent enough Fluke. I’m confusing myself where I tested from now…which points should I test across? Testing across COM and L1 when the switch is on, I read 135VAC. Across COM and L2 when the switch is off, I read 205VAC.

Cheers

I think you need to download diagram of intermediate switching and do as I did. With the power off do a continuity test. Unless you have 5m leads on your multimeter, you will been longer cables, as I said, used alarm cable, I had 30m siting at home and it is very light. I screwed one strand of the alarm cable in to a terminal on the ceiling rose, ran that cable down to the switch, wrapped it around one of the meter probes and then touched each of the cables in the switches with the other probe (after I removed the face plates).

Checking for voltages doesn't help that much if someone has messed up the commons.

BTW, I am not an electrician and have never previously worked on two way lighting, but thanks to the electricians here and the widely available images on the web, I was able to identify each cable and fix things. You really do need to use continuity tests with the power turned off sand the switch plates removed to help you draw your diagram and see if the existing set up is correct.


From that point you can then start to look at other things.

 

[Harry Bloomfield]

I was testing with a decent enough Fluke. I’m confusing myself where I tested from now…which points should I test across? Testing across COM and L1 when the switch is on, I read 135VAC. Across COM and L2 when the switch is off, I read 205VAC.

You are getting some strange values there, probably due to the type of lamp in the ceiling lamp holder.

Those switch back boxes appear to be properly earthed, I would suggest making all your measurements with reference to the earth. In other words connect one probe always to the earth terminal, and repeat your testing. You can expect to see perhaps a few volts even when a wire is not live <50v and >230v when live.

More definite than a meter for determining whether something is genuinely live, is a test lamp which applies a load on a live wire. Just an ordinary tungsten lamp, in a lamp-holder, with the two wires from the lamp-holder used as the test leads for live or not live.

 

[Harry Bloomfield]

I think you need to download diagram of intermediate switching and do as I did. With the power off do a continuity test. Unless you have 5m leads on your multimeter, you will been longer cables, as I said, used alarm cable, I had 30m siting at home and it is very light. I screwed one strand of the alarm cable in to a terminal on the ceiling rose, ran that cable down to the switch, wrapped it around one of the meter probes and then touched each of the cables in the switches with the other probe (after I removed the face plates).

Assuming the earth is properly connected all round, no need for any long wires, he can use the earth terminals instead for his continuity tests.

 

[opps]

Assuming the earth is properly connected all round, no need for any long wires, he can use the earth terminals instead for his continuity tests.

I do not doubt you, but can you explain how to do it? (pretty please). As I said, I am not an electrician, in the job that I mentioned, I thought it easier to go as basic as possible. BTW, in the case I outlined with the live in a back box bridging the metal back box, would that have made a difference?

 

[terryplumb]

Show us a pic of the wiring at the ceiling light . You should do some testing there . Voltages between...
Permanent live ( if present) to earth.
Permanent live to neutral.
Switched live to earth
Switched live to neutral.
Tell us the results.
The voltage readings taken at the switch are questionable if you have taken them only across the switches terminals.

 

[EFLImpudence]

Surely - Red with Blue; Black with Yellow.

It doesn't matter which way round

 

[EFLImpudence]

As it is, that would mean the light would be on all the time.

Perhaps the same has been done at the light.