lighting fault

[Noob2013]

Hi all,

I have a strange lighting fault which I'm trying to get my head round. I popped in to a family members house on the way home from work so didn't have a Meggar. However, i had a multimeter and also carried out an inspection and test on this property a couple of months ago and found no problems.

The fault is on the kitchen/dining lights. There is 4 x GU10 3 spot fittings (fitted with the LED GU10s) There is a 2g switch, each switch supplying 2 lights.There are 2 t&e's at the switch (perminent and switch for each set).

Whenever either switch in the kicthen was switched on the mcb trips.

On arrival, several led lamps had physically burnt out and in a right state! Removed all lamps and still tripping!

Disconnected one light from each set and mcb did not trip! Faulty fittings came to mind but 2 at same time seemed odd!

Replaced the lamps in the 2 fittings still connected and the lights came on. After several minutes they tripped so I thought maybe the cheap led GU10s were the cause.

I used my multimeter for supply at the lights instead. The problem I found was that either switch seemed to give a supply all 4 lights even though the switch wires cannot be connected as they are on separate twin and earth's from switch. I can't get my head around it!

Did a bit of testing with my multimeter and all the cables at each light appear to be in the correct terminals. I also testing it a few months ago and found no dead shorts or issues.

With the mcb off, I switched each switch individually and made sure that it was switching the 2 lights it should and not the other 2.iSo dead testing of the switches seemed like there was no interconnection between them and was switching correctly. But when circuit energised all the switch lives had voltage!

One thing I noticed when mcb off, I had 0.8v DC between the 2 switch lives at switch??

The only thing I didn't try was to physically disconnect the other 2 fittings, possibly faulty too?? back feed on neutral???

I am going back with my Meggar to test everything properly but I have recently done this and everything was fine. Just seems odd that the leds were burnt out and 2 fittings were causing the mcb to trip with no lamps in. Any ideas before I return would be much appreciated as I got to the point were I was thinking WTF!

All I can think is the other 2 fittings are faulty too and giving a back feed through the neutral but again doesn't sound possible with lamps removed and there are no electronic parts (only lamp holders)

Thanks

 

[Octopus]

Given that the information you had provided points at the fittings I would remove each in turn and conduct ir rests on the fittings. If this doesn't yield anything then an ir test on the light circuit has to bed your next step.

Hope this helps

 

[davesparks]

If both switched lives become live when only one switch is closed then it suggests that the switched live conductors are electrically connected somewhere. (Or its capacitively coupled voltage, but presumably you used a proper voltage tester at some point?)

 

[gnselectricals]

Will get a reading between switch lines etc due to capacitance if run in proximity. If lamp holders/ lamps burning out badly then I'd prob say replace entire fitting after IR test. Are they fire rated or open back fitting's, insulation around them or loose connections ?

 

[Noob2013]

Given that the information you had provided points at the fittings I would remove each in turn and conduct ir rests on the fittings. If this doesn't yield anything then an or test on the light circuit has to bed your next step.

Hope this helps

Thanks, that's the only thing I could think of once I had left and cooled down enough to rethink!

All the lights are exactly the same and there are no electronics inside so cant see how they would fail causing such a strange outcome. Each fitting literally consists of 3 GU10 lamp holders. And all 4 to fail at same time seems very unlikely.

 

[djelectric]

Remove all fittings and switches and bypass with wagos/terminal blocks..

Locate origin of the faulty part of the circuit only, could be looped from the hallway for example, wherever it starts (or ends, if its first in the chain from the CU).

Disconnect and test that whole length of cable, continuity and IR. If readings are ok then maybe you either have a bad switch or fitting or something was terminated incorrectly..

 

[Noob2013]

Will get a reading between switch lines etc due to capacitance if run in proximity. If lamp holders/ lamps burning out badly then I'd prob say replace entire fitting after IR test. Are they fire rated or open back fitting's, insulation around them or loose connections ?

Some of the led lamps were badly burnt but lamp holders look ok so i put it down to cheap led lamps.

They are not fire rated or open back and there is insulation above. The fittings are ceiling mounted. I checked all connections.

 

[Octopus]

Any new shelves put up or pictures on the wall?

 

[Adam W]

My first instinct would be that the fittings are wired up incorrectly, so the switched lives are connected to what should be the permanent live to the next fitting, which in turn is connected to the switched live at the next fitting instead of the live loop.
Maybe best to pull everything apart at the fitting and bell it out.

 

[Noob2013]

Remove all fittings and switches and bypass with wagos/terminal blocks..

Locate origin of the faulty part of the circuit only, could be looped from the hallway for example, wherever it starts (or ends, if its first in the chain from the CU).

Disconnect and test that whole length of cable, continuity and IR. If readings are ok then maybe you either have a bad switch or fitting or something was terminated incorrectly..

That's the plan when I go back. I already bypassed the switches as I thought they could be faulty but they are ok. I bypassed 2 lights but will do that with the other 2. There are several rooms which have a live and neutral fed from these fittings and they are all ok.

I did some belling out to make sure the other cables are terminated correctly and they are.

 

[Noob2013]

Any new shelves put up or pictures on the wall?

No nothing at all.

 

[Octopus]

Please update us with your findings

 

[Noob2013]

My first instinct would be that the fittings are wired up incorrectly, so the switched lives are connected to what should be the permanent live to the next fitting, which in turn is connected to the switched live at the next fitting instead of the live loop.
Maybe best to pull everything apart at the fitting and bell it out.

Yeah i thought that too after finding out it wasn't switching correctly.

So I checked the switch lives and they are in the correct terminals. I belled them out from the switch to the fitting and then onto the 2nd fitting. They are also blue with brown sleeving as they come from switch so it's also more obvious just by looking. I also made sure that when I switched the switches I didn't get continuity between live and switch live at the other 2 fittings. It only happens when circuit energised.

It is such a strange one that it just doesn't make sense.

 

[Noob2013]

Yeah will do Murdoch. It's probably something so simple that I've overlooked it! Don't think I have thought.

 

[Noob2013]

Just a thought.

Is it possible that the other 2 light fittings are faulty and back feeding down the neutral?

I would of thought any faults to cause this at these 2 fittings would be enough to trip the mcb or rcd.

I've been thinking again and still puzzled to how all the fittings come on when they have independent switches and the switch lives work as they should with the circuit off!

 

[HappyHippyDad]

Just a thought.

Is it possible that the other 2 light fittings are faulty and back feeding down the neutral?

I would of thought any faults to cause this at these 2 fittings would be enough to trip the mcb or rcd.

I've been thinking again and still puzzled to how all the fittings come on when they have independent switches and the switch lives work as they should with the circuit off!

Don't make it complicated! IR tests as suggested, plus take down the fittings and inspect/test the terminals, whilst the fittings are down put 2 normal pendant lights up to see if it still trips or if it now works. Plus draw out a diagram of the switches and lights to make sure all conductors are where they should be.

 

[Noob2013]

Don't make it complicated! IR tests as suggested, plus take down the fittings and inspect/test the terminals, whilst the fittings are down put 2 normal pendant lights up to see if it still trips or if it now works. Plus draw out a diagram of the switches and lights to make sure all conductors are where they should be.

Yeah I have been over thinking I think.

I have some pendants ready to put in later as well as a Meggar.

Fresh head today so hopefully go smooth.

 

[Octopus]

Don't make it complicated! IR tests as suggested, plus take down the fittings and inspect/test the terminals, whilst the fittings are down put 2 normal pendant lights up to see if it still trips or if it now works. Plus draw out a diagram of the switches and lights to make sure all conductors are where they should be.

I would take them down first!

 

[Lucien Nunes]

ither switch seemed to give a supply all 4 lights even though the switch wires cannot be connected as they are on separate twin and earth's from switch

still puzzled to how all the fittings come on

Do lamps actually light amongst both groups or do you simply mean you read a voltage? If the lamps light, but a continuity test between the two switched lives gives no reading, either the fittings have somehow got wired in some bizarre series arrangement and could never have worked properly, or a fault between the two SL's (e.g. screw through cables) is breaking down at mains voltage but tested clear to your multimeter. (I expect your original IR tests didn't include between the SLs). In any case if it was that marginal, I'd expect it to flicker and the fault to burn itself out eventually,
If you just meant there was a voltage measured at the 'switched-off' group, then capacitive coupling between the cables where they run together down the switch drop is the likely (harmless) cause. If the IR between them tests OK (SL of group 1 to SL of group 2) it wouldn't surprise or concern me. An approved voltage indicator would not have given the misleading reading.

One thing I noticed when mcb off, I had 0.8v DC between the 2 switch lives at switch??

Perfectly normal, there are capacitors inside the LED lights can store some residual DC charge which can leak back to the terminals while off.

 

[Noob2013]

Do lamps actually light amongst both groups or do you simply mean you read a voltage? If the lamps light, but a continuity test between the two switched lives gives no reading, either the fittings have somehow got wired in some bizarre series arrangement and could never have worked properly, or a fault between the two SL's (e.g. screw through cables) is breaking down at mains voltage but tested clear to your multimeter. (I expect your original IR tests didn't include between the SLs). In any case if it was that marginal, I'd expect it to flicker and the fault to burn itself out eventually,
If you just meant there was a voltage measured at the 'switched-off' group, then capacitive coupling between the cables where they run together down the switch drop is the likely (harmless) cause. If the IR between them tests OK (SL of group 1 to SL of group 2) it wouldn't surprise or concern me. An approved voltage indicator would not have given the misleading reading.



Perfectly normal, there are capacitors inside the LED lights can store some residual DC charge which can leak back to the terminals while off.

Thanks for the reply.

With mcb off:

- No continuity through SL1 and SL2 (just 0.8v DC)
- SL 1 operates 2 lights only and SL2 operates 2 other lights only (how it should work)

With mcb on and either switch on:

- Voltage at all lights
- all lights come on but within a few minutes mcb trips again

This is with 1 light on each set connected.

Very bizarre (technically possible) if there is a fault between SL's as no work has been carried out and they are in separates twin and earth's.

Will be IR testing tonight so hopefully find the answer.