MCB tripping

[TRAINEESPARKS]

I have an MBC on the downstairs lighting circuit that keeps tripping. I have recently installed Downlights and wall lights in a new extension in December of last year without any problems and this is the first time it had occurred. I have kept different lights on at different times and it still trips. It also tripped this morning when there where no lights actually on. Any ideas?

 

[Qedelec]

What was the insulation reading?

What is the total loading of the circuit?

Is there another B6 MCB you can swap the circuit to?

What is you supervisor doing??

 

[TRAINEESPARKS]

Clearly a lot of investigation needs to be carried out. The work was carried out by a qualified Sparks so I can only assume he did the correct calculations.
Would the MCB still trip if no lights were actually on? Does this imply a faulty MCB?

Thanks for the response by the way..

 

[Qedelec]

No worries

No it should not trip if there is no load.
Does it trip if the cable is removed from the MCB?

Make sure there is at least 0.5Mohm between phase and neutral/cpc.
Most likely cause is a nail somewhere.

 

[TRAINEESPARKS]

would that be a nail through a cable?

 

[Qedelec]

Unless you're sitting on one, yes.

But you need to do an insulation test first, you do have a insulation tester that can supply 500V @1mA, don't you?

 

[TRAINEESPARKS]

allow me to clarify the situation. I dont actually work as an electrician. I am at college half way through year 2 and hope to become one in the near future. I dont actually have a tester but will have a access to one through college. All the building work was completed in December-January so no nails have been put anywhere since then and everything has been fine until now. Would it take that long to take effect or would it be instantaneous?

 

[Qedelec]

No way of knowing, it could trip now or next week, it depends on too many factors.
First thing is to find out why its tripping, overloaded by the supplied accessories or by a leakage.

MCB's will handle much more than their rating, (look at the graphs in your regs book).

You'll be doing 2391 next then?

 

[TRAINEESPARKS]

at the moment its tripping every 30-40 mins if not more frequent. Still, its all good in helping me with my studies. Yes, i'll be going for as many qualifications as possible. The hardest part will be trying to get work without the experience, which I'm not looking fwd to at all.

Thanks for all your help and advice, its really appreciated..

 

[Qedelec]

it sounds like an overloaded MCB or a faulty one, as I said earlier prove it by swapping to another 6B mcb.

You might need to volunteer to work with a sparky FOC for the experience.

 

[PompeySparks]

Sorry to jump in but just wanted to say to trainee - I qualified fairly recently when electrical work in my area was very thin on the ground - as qed says you may have to work for free at first. It's all about not giving up after the 100th company has told you 'we're not looking to take apprentices on'. As my college tutor said at the time 'if you REALLY want to get into the industry, you WILL find a way' - best of luck mate!

 

[TRAINEESPARKS]

Thanks PompeySparks. Appreciate that. I am tenacious by nature so I will
certainly make those applications and not give up.

 

[dingbat]

TS, de-energise the circuit, then go around and check every switch plate, looking specifically for nipped cables. I've come across this problem quite a few times and in each case a decorator was involved!

If that doesn't uncover anything you need to embark on a logical sequence of tests to isolate the faulty section/connection. Ask your college lecturers how to go about this.

 

[TRAINEESPARKS]

OK .. the plot thickens. After about a week of no tripping whatsoever
it started again last night. It must have tripped at least 10 times in the space of an hour. Then it occurred to me that the last time this happenned it had been raining heavy, as it was last night!!

any ideas?

 

[Qedelec]

OK .. the plot thickens. After about a week of no tripping whatsoever
it started again last night. It must have tripped at least 10 times in the space of an hour. Then it occurred to me that the last time this happenned it had been raining heavy, as it was last night!!

any ideas?

Close the window!!! Repair the roof!!!