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

 

[Richard Burns]

0.09 Mohms on an IR will not trip any MCB, so you still need to look further for the fault.
Try testing on a continuity tester to find the fault.
Because this has just happened, there must be a proximal cause. Since there has been no work done the obvious is changing light bulbs and moving a fitting whilst doing it. The possible other is rodent damage, but slightly less likely on a mid level circuit.
An MCB tripping will usually be a clearly obvious fault somewhere so start with looking at light fittings and the cable connections as roses, then start on the splitting of the circuit.
Check at the ceiling roses for numbers of cables to indicate where the end of the circuit is and where there may be a branch in the circuit. Could easily be clock wise and branch off to lounge, but also many other options.

 

[guest119]

Anything spurred off it or fixed equipment like a bell transformer or a central heating pump?

Boydy

 

[GLENNSPARK]

yes...

like is it doing it at certain times of the day?....

 

[Silly Sausage]

G'day mate, could you try a thumper test on it to find the fault?!

 

[Guest55]

G'day mate, could you try a thumper test on it to find the fault?!

dont forget to reset your "arc fault combo"
;-)

 

[Guest55]

anyways , is there an outside light on this circuit ?
start there seeing as its rained every day for 3 bloody weeks

 

[GLENNSPARK]

G'day mate, could you try a thumper test on it to find the fault?!

here...i`v found the inspector & tester with a young apprentice in pocket...

 

[Matt85]

Any fluorescent lights ect in circuit? Choke failed maybe?

 

[Marvo]

....I specialise in HV work, up to 33KV, high voltage distribution, oil/vac/SF6 Circuit breakers, protection of distribution, busbars, HV transformers and things like that

If the circuit holds for a while then maybe you could install an auto vacuum recloser

 

[J@mes]

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!

 

[camerabloke]

i bet the cables are shoved up in the void above that light mate

 

[GLENNSPARK]

rite then..

any outside lights?

 

[Guest55]

rite then..

any outside lights?

if that was deadpan sarcasm , brilliant.
if that was serious , then wake the **** up.
;-)

 

[Octopus]

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

 

[telectrix]

was it this mouse by any chance?

Mouse Trap Survivor Cheese Commercial - YouTube