Difficult fault to find?

[Octopus]

Is the lighting circuit wired as loop in or neutrals at switches?

With so few lights narrowing it down to a section shouldn’t be too tricky.

Had this recently and mice were to blame .....

 

[HappyHippyDad]

You bought an air rifle to shoot an animal even though this was against your beliefs ? Surely a humane trap would have been a smarter buy ?

Good to know that threatening it worked well enough anyway

T

Is the lighting circuit wired as loop in or neutrals at switches?

With so few lights narrowing it down to a section shouldn’t be too tricky.

Had this recently and mice were to blame .....

Neutrals are in the light fittings.

 

[Octopus]

Neutrals are in the light fittings.

I’d slowly taking it apart .... another one from the mists of time was where the switch drop cable had been trapped and damaged where boards had been laid in the loft, and the board pinched the cable as it entered the metal conduit .....

You will be really chuffed when you solve this

The necessary ingredients are patience, paper, pencil or pen and your test kit .. and a customer knowing that the bill will only be known when it’s done and dusted

 

[johnduffell]

don't let the IR test mislead, remember it would only be accurate for a linear resistance. The MCB will trip on reactive power as well as real power but with DC IR testing you'll only notice what would transfer the real power.
Could be a faulty PSU somewhere causing the issue perhaps.
Or it could be the mouse!
Can you get a clamp meter on the circuit when the MCB is on?

 

[UNG]

I may have to do that, but I was hoping to track it down with fault finding/testing rather than undoing everything on the circuit.

There are only so many tests you can do before you have to undo something and test again this may need to be repeated a number of times until you find the fault
If the fault is big enough to allow a circuit tracer to function you can sometimes use this to take you to the fault without having to break the circuit down

 

[HappyHippyDad]

don't let the IR test mislead, remember it would only be accurate for a linear resistance. The MCB will trip on reactive power as well as real power but with DC IR testing you'll only notice what would transfer the real power.
Could be a faulty PSU somewhere causing the issue perhaps.
Or it could be the mouse!
Can you get a clamp meter on the circuit when the MCB is on?

Yes I could, but would this not just show the 1 or 2 A running through it at that time? It may change rapidly when it's about to trip but I don't think I can get away with standing there for 30 mins
Anyway, I am now leaving to find it!

 

[Barnaby Stedman]

found the fault?

 

[HappyHippyDad]

found the fault?

Just found it!
L/N -E results were now 0.03Meg. Traced the fault to between 2 lighting points.
Unfortunately this was between the main house and flat roofed extension.
Traced the cable in the loft where is disappeared into the cavity between main house and extension.
Crawled to edge as far as I could and poked the inspection camera down into the cavity.
This is what I saw..

Sorry for poor quality but this is me taking a picture with my phone of what the inspection camera was seeing.
Looks like the naughty mouse!
Ps.. looks like he's started on the socket cable nearby as well which you can just make out in one if the pics.

 

[James]

Just found it!
L/N -E results were now 0.03Meg. Traced the fault to between 2 lighting points.
Unfortunately this was between the main house and flat roofed extension.
Traced the cable in the loft where is disappeared into the cavity between main house and extension.
Crawled to edge as far as I could and poked the inspection camera down into the cavity.
This is what I saw..
View attachment 49768 View attachment 49769 View attachment 49770
Sorry for poor quality but this is me taking a picture with my phone of what the inspection camera was seeing.
Looks like the naughty mouse!

congratulations.
bet you feel better already.

 

[Barnaby Stedman]

congratulations.
bet you feel better already.

i expect his customer now expects him to fix it though!!

 

[DPG]

Nice one !

 

[HappyHippyDad]

congratulations.
bet you feel better already.

Yes!
I should have found it first time round really but stupidly disregarded the 0.3Meg to earth, which is now 0.03Meg.
Soon to be >999 Meg!

 

[Wilko]

Good job HHD !
Can I ask what inspection camera you’ve used?

 

[HappyHippyDad]

Good job HHD !
Can I ask what inspection camera you’ve used?

This one RIDGID micro CA-150 Inspection Camera - https://ridgidtoolshop.co.uk/hand-held-video-inspection/ridgid-1597-micro-ca-100-inspection-camera.html?gclid=Cj0KCQjwitPnBRCQARIsAA5n84ny7m9xdD6ESuZvE-RkBuYkSHX6ae3u0_qG0_uAQh_h4tJ-pTyxQZoaAuPlEALw_wcB
I'm sure it must be able to take a picture somehow at that price but I dont know how to do it!

 

[Baddegg]

Nice job HHD......had a bit of a run around myself today with a rfc taking out the rcd.....turns out the rfc did the whole house, 3 floors! Found it in the end.....someone years ago had left a flex connected to an old jb and just taped the other end up and left it in the dirt under the house!

 

[telectrix]

connect the camera to your pc/laptop. then use the mouse. oops. mouse has chewed cable. plan B.

 

[FatAlan]

Just had a call from a friend with a 32A MEM Type 1 on a RFC tripping with supposedly all loads disconnected. Looking forward to a good ferret tomorrow. Pardon the small fury mammal pun!

 

[telectrix]

furry as in animal. . fury is rage.

 

[Baddegg]

Just had a call from a friend with a 32A MEM Type 1 on a RFC tripping with supposedly all loads disconnected. Looking forward to a good ferret tomorrow. Pardon the small fury mammal pun!

Same fault here Alan....this board was sector!

 

[FatAlan]

furry as in animal. . fury is rage.

Too right Tel. They’re also a family from the Manchester area I believe, one member is quite good at boxing

 

[magnoliafan89]

This one RIDGID micro CA-150 Inspection Camera - https://ridgidtoolshop.co.uk/hand-held-video-inspection/ridgid-1597-micro-ca-100-inspection-camera.html?gclid=Cj0KCQjwitPnBRCQARIsAA5n84ny7m9xdD6ESuZvE-RkBuYkSHX6ae3u0_qG0_uAQh_h4tJ-pTyxQZoaAuPlEALw_wcB
I'm sure it must be able to take a picture somehow at that price but I dont know how to do it!

----ing how much?!?!?!

 

[HappyHippyDad]

****ing how much?!?!?!

Yeah but I'm sure it does all sorts of clever things.... I just don't know how to use them and probably never will!

 

[ipf]

Yeah but I'm sure it does all sorts of clever things.... I just don't know how to use them and probably never will!

Don't give upon it...……...after all, you've just learned another way of finding a fault....and that was impossible 24 hrs ago.

 

[PEG]

Too right Tel. They’re also a family from the Manchester area I believe, one member is quite good at boxing

Not just one

 

[johnduffell]

Yes I could, but would this not just show the 1 or 2 A running through it at that time? It may change rapidly when it's about to trip but I don't think I can get away with standing there for 30 mins
Anyway, I am now leaving to find it!

Glad you found it! If you put 10a through a 6a mcb it will take a while to trip, and it wasn't clear if the trip was from overload or fault. The idea was also to work out if it's going down l-n or l-e or l-cpc.
Glad you're sorted though!

 

[Lucien Nunes]

it wasn't clear if the trip was from overload or fault

I think it was though. HHD reckoned on a couple of amps load on the circuit, and anything else consuming 1500VA or so would have made its presence felt. Had the MCB been tripping through being on the threshold of its current rating, a) it would have been warm which HHD would hopefully have noticed and b) the tripping would be more cyclic than random. It's useful to consider the power dissipated at a suspected fault and what damage it would cause. 1500W dissipated at a point fault would soon set it on fire or melt it so extensively that it could not have remained as it was to cause another trip. So it had to be an intermittent short-circuit, that did not blow itself clear completely on account of the low rating of the MCB and moderately high resistance of the small cable. Had the same damage occurred on a cooker circuit near the board, it would be more likely to blow itself apart at the first bang.

It had classic symptoms of a damaged cable - very low IR L-E and N-E with occasional tripping of the MCB. There was no certainty that each of the abnormal symptoms was related to a single fault but the principle of Occam's razor would suggest so. Easy to analyse with hindsight, of course.

 

[johnduffell]

Agree totally and thanks for the analysis, i only wanted to add it to the mix as a consideration as no point in saying "i thought that originally" after the fact!
Just a couple of points that may be interesting..
If an MCB trips in overload it can trip again quickly due to it already being very warm
Also the fault i suggested was a faulty psu for lights or similar. A transformer with shorted windings can warm up a lot without causing a fire

 

[pirate]

somebody had to do this...
https://www.google.com/search?clien...d+together+in+a+cave+and+grooving+with+a+pict

 

[Genlight]

A great thread complete with a result, thanks Happy for taking the time to give us the result.