Live/Earth fault on domestic lighting - a little help please!

[J@mes]

Afternoon all, just after a bit of advice!

The MCB for my downstairs (and landing) light started tripping the other day and now won't go back in. There is a direct short between the live and earth (0.09 on the IR) whereas the live/neutral is 204M and the neutral/earth is 194M.

As a commercial electrician/HV type, I've not had much training or much understanding on how the domestic guys wire houses, how they decide which ceiling rose is first, which is last etc so is there any proper pattern to it or is it just a case of disconnecting at each rose and testing another one until the fault disappears?

As you can see above (for some unknown reason it's up there ^^^ ) I have drawn a (highly) technical drawing showing the layout and where the ceiling lights, wall lights, CU, and the direction of the first cable run for the lighting circuit.

Any advice (and not too much mocking!) would be appreciated!

Cheers

 

[7029 dave]

I had a customer with this issue..... mice had eaten their way through both layers of insulation AND the copper!

Yep, the little gits love a bit of pvc.

 

[Plonker 3]

Had a fault the other day, sockets keep taking out the RCBO, been happening for quite a while. Only just thought to get some one too look at it.

IR 0.01M on L-E, got lucky and first socket I took off was the fault. Customer had flush sockets on 25mm back box, crushed cable.it had completely blown the live conductor in 2 where the fault was, CPC fell off quite easy too.

 

[GLENNSPARK]

was it this mouse by any chance?

Mouse Trap Survivor Cheese Commercial - YouTube

dont know how many in here have worked out this little piece of sarcasm Tel....lol...

 

[jaypp]

Just to answer a few questions....

No outside lights
No pattern to the fault, tripped once on sunday afternoon, then tripped twice more in the evening and then wouldn't go back in at all, even with all lights off/ lamps out
No spurs off, with the circuit isolated everything else in the house still works


Just dropped a fitting in the lounge, this appears to be a spur off as there is just the switched live, neutral and earth in connector block to the fitting, no rose. There is rodent damage on the cables (we have a few mice knocking around, saw the evidence while piping new radiators)

Gonna drop a few more fittings and see where we are.....and how much the mice have eaten!

could that be somewhere to start?

 

[PEG]

I concur, poking,notching,drilling,heaty rubby shiny copper...had this a while back where the downstairs light circuit between the joists was providing a handy mid-way support for a run of two 15mm rad pipes. Had to section the board above ,that should have been lifted to fit noggin and clips...

 

[Geordie Spark]

I went to a house to fit a new radiator which was longer than the existing one so it was carpets & boards up to modify the existing pipework and there it was .... pipes laid in notched joists and cables laid on top of them along their length and the board had been screwed hard down on them squashing them flat against the pipes.

What had started as the easy job and not very lucrative job of replacing a radiator turned into something worth doing!

 

[J@mes]

Piping was only from just under the boards up to the TRV/LS, so nothing else was disturbed or altered :smile5:

 

[telectrix]

don't be toos ure. wet-pants can damage cables just by being in the same room.:nuke:

 

[J@mes]

was me who did it

 

[Geordie Spark]

don't be toos ure. wet-pants can damage cables just by being in the same room.:nuke:

I'm not THAT bad.

 

[J@mes]

Solved, strapper on the hall two way lighting was down to earth so it's been disconnected for now as I am having a new set of banisters/spindles fitted and where the chippy is working is right on top of the boards I need to lift.

L-E 309M, L-N2 299M and N-E 412M



edit: Just like to say thanks for all the advice, info and banter!

 

[telectrix]

nice to get the feedback and well done for sorting it.

 

[J@mes]

Update No 2, finally got the landing floor up and.......

 

[Clive P]

Hi,

Back to your post, last year wired my brothers flat for him. I get a phone call, when I turn the lights on I get sparks at the MCB ( trying to reset it). So I say, don't touch anything until I get there, when I arrive screw straight through the strappers directly above the switch!

Regards.

 

[not clever]

Might have cured your mouse problem.