MCB tripping in bedroom light circuit

[joethelips]

Hi, having a problem with MCB tripping for lights in a two bed flat. Would appreciate any help.

Problem started before xmas. MCB tips sometimes if either light is switched on. Time can vary from few mins to 30 mins but can even trip before I've a chance to turn either light on i.e. seconds after resetting MCB switch.

Had an electrian round to look at wiring of both light fittings and both tested fine with multimeter- MCB wouldn't trip when he was around. Wiring looked fine also.

Came back after xmas and had left heating on by mistake for 5 days (nice gas bill due!). Lights worked fine for a few days.

MCB back tripping again as before. Upstairs neighbours came back last night from xmas hols and problem started again today.

There was a previous problem over a year ago where they'd a leak in shower which is above one bedroom. Left water marks on our ceiling.

Is this a coincidence? I don't see any new water damage but if they used shower this morning could this be the problem?

Could the excessive heat have resolved problem while they were away?

One other coincidence was one socket never worked in bedroom and about same time as first time MCB tripped this socket started to work again. This socket still works.

I've tried turning switches on this socket off and all other sockets off but MCB for lights still tripping.

Could there be a faulty wire connection in this scoket causing a short circuit? All scokets on a different circuit.

Apologies for long winded post and I'm guessing I'll need an electrcian back out but any suggestions or comments would be really appreciated.

Thank you,

Joe

 

[ricicle]

A normal multimeter will not perform the correct insulation test required to find a fault. Did the Electrician use an Insulation Resistance tester ?
It sounds like you have some sort of damp or rodent damage somewhere.

 

[joethelips]

Not sure what type of multimeter he used. All I know is he tested light fittings and said they were OK.

He was out to fit a new light and didn't have much time to investigate problem.

Thanks for your help. I'm guessing myself its a damp problem and will speak to upstairs to see how well they insulated their shower from the last time there was a leak

 

[joethelips]

Have had a look on Google this morning and on Youtube and it doesn't appear that the multimeter the electrician used was an Insulation Resistance Tester - based on instruments I saw on video.

Does this test detect if there is damp or will it just detect a problem with resistance, which I suppose would be a good start as it would help locate problem?

Light fitting is a rose ceiling light and when I unscrew the fitting at the ceiling the hole is quite small, with just enough space provide for wires to protrude.

Could this test be carried out on the wires that hang down or would it need to be done over a longer length?

Again, any help would be very much appreciated.

 

[wingcoax]

A Megger( insulation tester) will reveal if there is a problem with insulation, i.e water damage. Any COMPETENT electrician would use one to find the fault. It can probably be done using the exposed ends.

 

[joethelips]

Many thanks for your help.

I will contact a qualified electrician and request that this test is carried out.
This would be easier than asking upstairs neighbours to take up their shower unit, as not sure how well they'd be willing to do that!

If the test proves that this is the likely cause then I will insist that they have a proper look at their shower unit, unless the electrician can suggest another solution to fix any insulation problems - but I'm guessing that the source
of the problem is what needs to be addressed - fix any leaks!

Thanks again

 

[JohnD]

you could loosen the light fittings from the ceiling (they should have a bit of slack cable) examine them for any signs of damp, and see if having them exposed to the air improves things.

There are not supposed to be any hidden junction boxes. Cable is waterproof but most connections are not. If someone has hidden a junction box under the upstairs floor (e.g. for an extractor fan) it will be prone to wet problems. You might also be able to smell damp when you remove the ceiling roses.

A slight bathroom drip often evaporates away without leaving much of a stain, especially if it only happens intermittently when a fitting is in use.

If leaving the light on seems to cure the problem, it will be because waste heat from the bulb keeps the rose hot and dry (especially if you use a filament bulb, not an energy-saving lamp)

Showers over baths usually leak round the edge of the bath. Any waste pipe can leak. Water can run along the upper suface of plasterboard quite a long way until it finds a hole to drip through.

If the ceiling has been damaged by damp you are entitled to have the wet plasterboard pulled down and replaced, with a claim against your neighbours insurance. Take the opportunity to inspect and/or replace any electrical items exposed by the hole. Also leave it open for a while to watch for any continuing leaks. Foil-backed plasterboard is waterproof on the top surface.

 

[joethelips]

Thanks for all your advice and help. This is a great forum!

Was taking another look at the rose ceiling light tonight to see if I was to take it apart I might be able to see into the ceiling space. Turned the MCB on so as the light was working in the room.

Heard the bang and it came from outside flat. There is an outdoor light in back garden that we never use as no bulb in it. Turned MCB back on and I could see sparks at end of wiring before it entered light casing and could hear a sizzling noise.

So I'm guessing this is the source of the problem as outdoor light must be on same MCB and insulation has worn away and its wet outside!

I'm sure I could buy insulation tape and try and seal the exposed wire but
think I'll call an electrician and make sure it's all done properly and safely.

Thanks agin for your help.

 

[wingcoax]

DO NOT repair with tape. The length of cable needs replacing, or, at the least, repairing with a weatherproof junction box.

 

[joethelips]

Now that I know what the problem is and know its not as big a job as I feared and doesn't involve lots of time and money, I'm more than happy to get it fixed by a competent electrician.

 

[wingcoax]

GOOD MAN

 

[ban-all-sheds]

If you don't want to use that light then find out where it's connected and disconnect it.