MCB Tripping On Lighting Circuit - Out Of The Blue?

[EViS]

Firstly, we have not altered any of our lighting circuits in years. Nevertheless, yesterday, the MCB on our Consumer Unit for our upstairs lighting circuit tripped. We switched it back on and a couple of seconds later, it tripped again, we once again we flicked it on and it stayed on all night. This morning, it tripped once again, and then again after we turned it back on.

Before calling out a sparky, is there anything obvious we can check that could be causing this (light bulbs, 12v transformers, etc.)?

ps. I'm not a qualified electrician, but have done my fair share of non-notifiable work so am competent in that respect. However, this scenario has baffled me.

 

[pjcomp]

If you've not touched anything then quite possibly it's the MCB itself. If you feel competent/happy enough, move the offending circuit to another MCB, see if the fault goes with it. If it doesn't, it's the MCB; if it does, you'll need to look somewhere elsse but at least you've ruled out the MCB

PJ

 

[EViS]

Interestingly, and I forgot to mention this in my opening post, I did change the MCB yesterday with another one on a different circuit. It is after this point that the MCB stopped tripping, until this morning.

 

[ricicle]

Possibly something faulty on the circuit which has 'weakened' the original mcb hence the swapped one working for a while. Get the circuit checked before you end up frying another breaker !

 

[EViS]

Anything else, which would be fairly obvious, I can check prior to calling a sparky in?

 

[ricicle]

Look for burnt out lampholders, loose connections, overheating transformers, tired extractor fans, worn switches etc

All checked safely with the power isolated.

 

[EViS]

Would a sparky, with their testing equipment, be able to find this fault considerably quicker than me? Or would he still manually have to check every single transformer, switch, and other connections?

Also, how would a connection loosen on its own? From the copper expanding/contracting over the years?

 

[maltaron]

You ask "how can a connection become loose". Mains electricity is alternating current at 50 hz or cycles per second, that means that the voltage is alternating between +volts and -volts 50 times a second. This results in minute vibrations in connections which over a period of time become loose.

 

[JohnD]

it might also be a cable that has ben badly installed, for example squashed between a floorboard and a hot pipe. The heat will make the insulation soften and degrade, and the pressure of people walking on the floorboard will damage it.

If it happens when people are walking around the house, see where they stepped.

It can also be water dripping into a light fitting or a junction box. Likely to be under the bathroom, especially if someone has poked holes in the ceiling for downlighters, but could be a loft leak..

 

[sparkwright]

Something in a loftspace crushing a cable.

Recently drillled hole in the wall, eg hanging a picture.

 

[mbga9pgf]

Something in a loftspace crushing a cable.

Recently drillled hole in the wall, eg hanging a picture.

How about cobwebs/zapped spider between live and neutral?

 

[EFLImpudence]

Are cobwebs and spiders rated at more than 6A and subject to intermittent resurrection?

 

[mbga9pgf]

Are cobwebs and spiders rated at more than 6A and subject to intermittent resurrection?

could be putting it back into vf every time the light is switchedon!