Testing on internal light circuit

[impish15]

Hi

I know I have to do more testing but I just want to see if there is something I’m missing.

Customer said light fitting in the loft was crushed causing the breaker to trip. I thought easy fault to rectify which was very naive of me.

I arrived disconnected the damaged switch which was in fact a plug socket switch used to power the TV ariel. Reset the MCB for the light which is not RCD protected and the MCB didn’t trip anymore but now there was no power to upstairs lights.

What have I missed? Customer said there was power before. I didn’t take my tester as I thought easy fix and I didn’t want to start testing at 9pm. I’m guessing possibly the customer hasn’t told me the full story. There is power at the MCB but nothing at the lights. She has halogens everywhere upstairs with signs of burning (I pulled 3 whilst I was looking in the loft surprised there hasn’t been a fire with the amount of “rubbish” in the loft).

Any advice/suggestions welcome please.

Thanks in advance

 

[littlespark]

How many cables were at the tv socket?
It sounds like you’ve just disconnected the wires and left them separated…. If it was a looped supply… ie, 2 lives, 2 neutrals,… then they’ll have to go back joined through.

Left a joint with a loose connection? Either on the live or neutral?

Power at the mcb…. So you at least took a voltage detector with you.
Go around all the switches, check live to earth until you find where it’s stopped… narrow down the area where the fault could be.

What kind of wiring system? Loop in at ceiling rose, loop at switch or central joint box?

Halogens are indeed hot, and a serious fire risk.
If 12v halogens, you have the added heat source of the transformers to worry about too.

Good luck on your search.

 

[impish15]

How many cables were at the tv socket?
It sounds like you’ve just disconnected the wires and left them separated…. If it was a looped supply… ie, 2 lives, 2 neutrals,… then they’ll have to go back joined through.

Left a joint with a loose connection? Either on the live or neutral?

Power at the mcb…. So you at least took a voltage detector with you.
Go around all the switches, check live to earth until you find where it’s stopped… narrow down the area where the fault could be.

What kind of wiring system? Loop in at ceiling rose, loop at switch or central joint box?

Halogens are indeed hot, and a serious fire risk.
If 12v halogens, you have the added heat source of the transformers to worry about too.

Good luck on your search.

Just the 1 cable for the TV ariel which I left disconnected and no further tripping

Yes the voltage dectector showed power at the MCB. The lighting circuit was wired in via loop in at the “ceiling rose”. Ceiling rose comprised of cables going into a connector block and then wrapped up in tape and left under insulation.

Many thanks I’ll carry out the live to earth as you suggest.

Fingers crossed I’m not there past 10pm again tonight

 

[littlespark]

There wont be many ceiling roses if its all halogen downlights..... Im suspecting a mess of joints up there.

Methodical testing.... each rose, or joint box should have a permanent live, switched live and neutral.... and of course the cpc. Maybe several switched lives coming off if they spider leg out to individual lights.

Leave everything tidier and safer than you find it. If a joint even looks suspect.... redo it.


There really is no such thing as a "5 minute job"

 

[impish15]

There wont be many ceiling roses if its all halogen downlights..... Im suspecting a mess of joints up there.

Methodical testing.... each rose, or joint box should have a permanent live, switched live and neutral.... and of course the cpc. Maybe several switched lives coming off if they spider leg out to individual lights.

Leave everything tidier and safer than you find it. If a joint even looks suspect.... redo it.


There really is no such thing as a "5 minute job"

Thanks for the advice. Much appreciated.

And yes I’ll never assume again a 5 minute job. Lesson learned

 

[impish15]

Just an update fault identified and rectified.

The power cable coming from the consumer unit to power the upstairs lights had a damaged cable, look like a burnt cable to me.

The IR test at the board showed a low reading for L-N, L-CPC, N-CPC. This confused me because the MCB didn’t trip at all. The MCB wasn’t RCD protected but I assumed the MCB would have trip because there was contact between L, N and CPC.

Have I missed something?

 

[littlespark]

If the cable was damaged, and broken through on either the L or N, that would stop everything from working.
If the act of examining the cable then disturbed it enough so cores were touching, that would show up as a short when testing.

Or, you may have a faulty MCB that isn’t tripping out as it should… is it old? Does it feel “softer” than others as you switch it on?

Was this damaged area close to halogen lights?
I’d be visually checking every cable up there, as it could happen again.

 

[DPG]

A low IR reading wouldn't necessarily trip an MCB. It would have to be very very low. What readings did you get?

A resistance test (ie. low Ohms) would have been useful.

 

[impish15]

If the cable was damaged, and broken through on either the L or N, that would stop everything from working.
If the act of examining the cable then disturbed it enough so cores were touching, that would show up as a short when testing.

Or, you may have a faulty MCB that isn’t tripping out as it should… is it old? Does it feel “softer” than others as you switch it on?

Was this damaged area close to halogen lights?
I’d be visually checking every cable up there, as it could happen again.

The MCB looks old. I couldn’t tell if softer but I’m back there Sunday to swap out the halogen lights so I’ll have a look then.

Yes the damaged area was close to the halogen light. I’ll have a look at all the cable when I’m down. I’m also using junction box to replace the connectors wrapped up in electrical tape

 

[impish15]

A low IR reading wouldn't necessarily trip an MCB. It would have to be very very low. What readings did you get?

A resistance test (ie. low Ohms) would have been useful.

I could be wrong as I was very tired at the time but from memory the IR test was 0.2. The resistance test from memory was possibly 6.09

 

[DPG]

I could be wrong as I was very tired at the time but from memory the IR test was 0.2. The resistance test from memory was possibly 6.09

That's 0.2M though, not 0.2 Ohms. Huge difference.

Was the 6.09 in Ohms?

Units are very important.

 

[impish15]

That's 0.2M though, not 0.2 Ohms. Huge difference.

Was the 6.09 in Ohms?

Units are very important.

I wish I took a photo now as I honestly can’t remember. All I know at the time I got results I was expecting but in hindsight I should have recorded the readings for reference.

The 6.09 was in Ohms