Tripping mcb - lighting circuit

[matt1386]

Morning guys, im looking for a bit of advice please

A friend of mine has rang me asking if I could have a look and see if I know why their lighting circuit keeps tripping

They know my situation ( a trainee ) and ive explained I will have a visual look and see if I can notice anything obvious, but anything more than that they will have to get somebody in

There have been no problems on the circuit until yesterday and no light fittings have been changed

They said it would stay on for a couple of minutes, and then knock off again

I went round yesterday, flicked it back on and it held while I was there ( around 20 minutes ) but by the time they got home it had tripped again

Could somebody please tell me what basic inspections I can carry out please ? ( I dont own any test equipment and to be honest dont know how to use the equipment correctly so thats out the window)

I was thinking of checking for loose terminations on all fittings and switches, any outside lights that could be on the corcuit and full of water etc.. Any blown bulbs... Anything else guys ?

Im just not sure why its taking a different amount of time to trip the breaker ?

Thanks very much

 

[Marvo]

I guess you could isolate the circuit using the MCB and visually check everything. I'd be looking for stuff that's been added like outside lights and checking areas where any work has been done such as hanging pictures ar anything involving a drill or masonry nails. Without test equipment your options are pretty limited.

 

[Simonslimline]

Sounds like the thermal trip in the MCB is going , once it reaches its tripping temp it lets go. What size MCB is it and whats the total load on the circuit?

 

[Simonslimline]

Possibly rodents aswell!

 

[matt1386]

Cheers for replies guys, just been over for a quick look as i had to get back home for somebody coming

The breaker is a GET B6, consumer unit is located in kitchen

breaker trips even with all lights off after a few minutes

The only lights that work in the house when the breaker is holding are the kitchen ones ( there are 2, and both the closest to the C.U, no power going to any other ones at the pendant or switch

At one point i turned the kitchen lights on, and the lamps were very dim with a slight buzzing coming from C.U

There is only 1 cable going to the fittings

7 pendants overall in the house

Checked all connections at switches, pendants and C.U and all seemed fine

Any ideas guys ?

Thanks very much

 

[happysteve]

(Warning! Trainee answer!)

Clarification: you say, "The only lights that work in the house when the breaker is holding are the kitchen ones (there are 2, and both the closest to the C.U, no power going to any other ones at the pendant or switch)."

Do you mean that there is only one lighting circuit? (like my old house)? And the two lights nearest the CU (in the kitchen) are sort of working, but a bit dim, and that the other ones (further from the CU) don't work?

If this is correct, then it sounds like either the L or N has come loose in a junction box/pendant fitting that goes on to supply the other lights in the circuit. It is wafting around, and might be lightly resting on the other line conductor (so if L, then resting on N). Or it could be water damage leading to similar, but if the other lights further down the circuit aren't working at all then it sounds like summat's actually come loose.

If you're able to safely isolate, prove dead and somehow lock off, then you could start taking pendants/JBs apart to have a nosey. Ah, you've already looked in the pendants. Junction box under upstairs floorboards somewhere?

 

[matt1386]

Hiya Steve, cheers for the reply mate,

Yes just the one lighting circuit covering the whole house

The kitchen lights actually worked fine when the breaker was holding, apart from once when they came on very dim with a slight crackling coming from C.U, every other time they were fine until mcb tripped

And yes, no power at all going to any of the other lights

I actually told them I thought it could be a problem with a JB under the floor, but said I would get some advice on here first before doing anything else

Thanks mate

 

[Simonslimline]

Have you checked the MCB is sitting on the bus bar properly and the connection is sufficiently tight.

Check the connections in the CU also.

 

[matt1386]

Yes Simon, thats the first thing I checked mate were all the connections in the mcb, give them all a pull and all were tight, also tried nipping them up with screwdriver and they were all nice and tight

At college I havent got onto the installation side of things yet, im still on the science part so im very limited on what I know

But, if i was to link out at the consumer unit on that circuit, and then go round each pendant checking for continuity, would that then give me an idea of where the break could be ( if there is a break obviously ) ?

I do have a voltage tester which does continuity

Im just trying to save the old lass a bit of cash thats all, but obviously if its something that im not competent to do at this stage then she will have to get somebody else in who is

cheers

 

[Simonslimline]

You would really benefit from having a multifunction tester and a wondering lead as this would give you accurate readings.

Have you considered the mcb may be knackered? Try changing it possibly.

 

[matt1386]

Your right mate, I just cant justify the cost for it to be sat there as at the moment i dont have a clue how to use most of the functions on there haha !

Ill get a replacement breaker and try that then first

cheers buddy !

 

[happysteve]

Eh up again

Blimey this is the blind leading the blind here, isn't it?!? (no offense to either of you, more having a dig at myself really!). I bet the experienced guys are having a giggle at this, no doubt shaking their heads...

Anyway, aside from finding the fault... sounds like this old lass is a friend of yours. She's only got one lighting circuit in the house, and at the moment it doesn't work. It'll be dark in about 6 hours. Has she got enough lamps and stuff plugged into sockets that she'll be safely able to get around the house tonight without tripping over any extension leads? (You've probably already thought about this, sorry if it's obvious!).

In terms of fault finding - not done this on the course yet, and my previous experience is all extra low voltage stuff. Dead tests are safer than live tests, so if you can completely isolate the circuit, and have got a continuity tester and a way of making a wander lead, then yep you could use that to find where the fault is, even if you can't get to it!

The "two lights closest to the CU work, the other ones don't" is a gift of a clue. Use this information, and continuity tests if you can, to find it.

 

[Simonslimline]

Yeah I agree steve lol, the only way to solve the issue is to be there on site armed with the right tools etc.

Its guess work otherwise in all fairness.

 

[telectrix]

my first check would be to ensure that the MCB is sitting correctly on the busbar. very common problem is that the busbar sits behind the terminal, esp. with wylex. also swap the MCB. ( simin said this in previous posts ). then start looking for circuit faults.

 

[Sarz11]

I think this is interesting for trainees to read and work out or try understand haha. And telectrix is an old helpful boy he rarely shakes his head and is quite helpful isnt he. I learn loads off you lot!!! Owt i dont understand il look up or ask