MCB Tripping

[sherman0251]

I had a call to a house and was told that her MCB for the downstairs lights had tripped. She reset the breaker and it stayed on for a couple of hours then it tripped again. When she tried to reset it a 3rd time it wouldnt, just kept tripping so she left it off untill I came. When I got there I reset it and it stayed on for about 2 days. It has just tripped again. Any ideas before I start doin IR tests on Sun?
Cheers

 

[GaryMo]

You already knew she had previously reset the MCB for it to trip again so you also reset the MCB and left without any testing?
Do you have magical fingers?

You should have carried out an Insulation Resistance test there and then.
I certainly wouldn't have reset it.

 

[experience]

Do you have magical fingers?

lol

 

[sherman0251]

as it happens yes!!!!!!!!!!!!!!!! I appreciate constructive comments not critisism!

 

[GaryMo]

It was constructive. If a MCB has tripped numerous times previously then you need to perform tests to highlight the fault, not switch and hope.

 

[baldelectrician]

It may be the MCB at fault- do you have a current meter?

It has been raining quite a lot - is there an outside light full of water?

 

[sherman0251]

I understand that but the woman I went to see was in her 80's wasnt really all with it and couldn't explain what was exactly was happening! at first she said her lights came on, on there own during the day and obviously that cudnt happen!When I got there it had tripped so I reset it and it was fine, operated all the lights numourous times and nothing tripped! So I was unsure as to whether there was a fault or not! She rang me yesterday saying her lights have gone out so now im going to have to terst for a fault!

 

[sherman0251]

thanks bald electrician ill have a look when I go tomorow! I havent done much fault finding just new installations so a little bit lost when it comes to these kind of things!

 

[GaryMo]

Start with disconnecting the line and neutral from the consumer unit, connect them together and test IR between the connected pair and the CPC (whilst still connected). Make sure all switches are in the on position and operate any 2-way circuits once and test again so both strappers are included.

I say line and neutral to earth as you don't know exactly what's connected to the circuit and can't say for definite if every voltage sensitive piece of equipment has been disconnected.

You're looking for a value greater than 1Mohm when tested at 500v.
You can also test between line and neutral but to be safe on an unknown circuit I would only test at 250v.

 

[sherman0251]

Thanks appreciate the advice. Hopefully will get it sorted out tomorow! Will keep you updated! Appologise for earlier!

 

[333rocky333]

Sometimes Worth checking the lampholders, older people tend to have
poorer eyesight and use 100 watt lamps, often burning up the
lampholder/wiring

 

[RF Lighting]

A T2 lampholder should be able to take a 100W lamp without issue

 

[GaryMo]

Thanks appreciate the advice. Hopefully will get it sorted out tomorow! Will keep you updated! Appologise for earlier!

Hope all goes well

 

[sherman0251]

Just been to look at the fault! Put a 250v IR test across all cores and got 0.01 ohms! Looked around the outside of the house and found an outside light with a 3core flex coming out of it feeding a standard 13A double socket lying in a pot full off damp compost!
Dissconnected cable from fitting and bingo 200 Megohms between all cores!
Cowboys!
Thanks for everyones help!

 

[GaryMo]

It's very satisfying when you find the fault isn't it?