Long Distance Fault Finding.... Any Ideas Please?

[ian3012]

Right... before we start... I HAVEN'T SEEN THE JOB YET! :^O

this is a house i've worked in a lot, and i know well.. it's also 130 miles away... i'm gonna have to go there in a few weeks.... :_|

RCD tripping after a 'warm up' period.... trips after approx 10 mins, ....reset and it then trips at randomly short intervals... anything between 16 secs to a minute.

but it never trips straight away.

on the phone with customer, isolated fault down to one of the 7 lighting cct's in this house...( i put 4 of them in, but not this one)

in this lighting cct ( 6A mcb) there's 3 florrys, 1 pendant and 12 spotlights.

isolated fault further to a row of 6 spotlights which are switched seperately.

when these 6 spotlights are switched off... there is no fault

told customer to remove 6 x gu10 led bulbs ...

fault is exactly the same even when the bulbs are removed. headbang

i can't blame the rcd as the other 5 cct's work fine on it....

i can't blame the mcb as there's no fault when the 6 spotlights are switched off...

i can't say it's a hard wiring short, as the tripping is never instantaneous...

can i really blame a light switch? lol.....

as i said, it seems like the cct has to 'warm up' before the rcd starts tripping..

obviously when i get there i'll do IR test and RCD ... but other than that, i just wondered if anyone else had seen anything similar to this?

or am i being a bit slow and missing the obvious?

it was rewired 7 years ago... f & j 2000 (?) dis board (seems cheap and nasty, but nice neat wiring job).... tns supply... all earthing and bonding is good when i looked at it 6 months ago.

 

[Theorysparky]

are these spots 1st floor ?

rodent damage ????

 

[ian3012]

in a kitchen with flat roof.... it's felted but there was no evidence of leaking last time i was there....

i don't know about rodent damage....

but if you're hinting at rodent damage causing a short, that would be an instantaneous trip?

 

[wozz]

ive repaired rodent damage cables that take time to trip, do you get many rodents in flat roofs?

Could be a cable laying on the lamp burnt insulation getting hot and then causing a problem?

 

[ian3012]

cheers guys.....

well if it is rodent damage it's a 'rip the ceiling down job'... cos it's a 'no access' flat roof... (this ceiling is 6M x 4M.... lol...)

i put led bulbs in these spots about 6 months ago.... there's no heat whatsoever from them... although the previous bulbs were 50watt gu10's.. so any heat damage would've been caused then....

but 6 months for a fault to materialise through burnt wiring???... i dunno....

i was hoping to avoid the ceiling coming down..... lol

 

[SPECIAL LOCATION]

Thought #1....

Damp/Moisture in a junction box, bridging 'L' or 'N' to eartrh?

e.g. have found J/b's that got packed full of insects, spider web sort of fluff and bits.. provided a path for moisture to bridge the conductors..

Not direct short but proportional to the amount of current flowing and/or the amount of moisture.

Thought #2....

Class2 (double Ins) spot lamp fitting, wired in T&E but nowhere for 'E' to be terminated.

Earth wire folded back or trapped between cable and cable-clamp in light fitting.

Fitting heats up.. Insulation softens bare (floating) earth wire make high res continuity through softened insulation due to pressure from clamp..

Turn lights off.. light cools down... PVC insulation hardens off again..

No continuity whilst cool!

Thought #3....

Say stuff this for a game of soldiers I am going down the pub! :Blushing

GuinnessGuinnessGuinnessGuinnessGuinness

ROTFWLROTFWLROTFWL

Thought #4

Send Brian?

I copied this one from Dekes answer sheet! ]

:coat

 

[sparkytim]

cheers guys.....well if it is rodent damage it's a 'rip the ceiling down job'... cos it's a 'no access' flat roof... (this ceiling is 6M x 4M.... lol...)

i put led bulbs in these spots about 6 months ago.... there's no heat whatsoever from them... although the previous bulbs were 50watt gu10's.. so any heat damage would've been caused then....

but 6 months for a fault to materialise through burnt wiring???... i dunno....

i was hoping to avoid the ceiling coming down..... lol

I would just drop all the fittings out and take a good look first before doing anything drastic, as others have said it does not take much for 30 mA to track if things are not as they should

I have twice found the remains of Slugs in JBs (Nice slime) as cause for tripping problems.

 

[ian3012]

thanx S.L. for spending some time on me....

#1... i can't see there being any j.b.'s in this cct, but to make sure.... the ceiling's coming down...lol...

#2... i'd like this to be an explaination.... but the bulbs are out of the fittings so no heat there.... i''l check anyway by pulling the fittings down.

#3... i'll use as a last resort.... :Applaud

#4... is brian any good at fault finding?... what's his hourly rate?

 

[ian3012]

thanks tim.... it's just the 'time delay' factor that makes this a tricky one i feel...

 

[batty]

Are they open fittings or fire rated?

 

[ian3012]

they're enclosed and fire rated .... long cylinders with vent holes at the top....

 

[superspark]

hi m8

i,d bet poss burnt cables from heat of spotlights i had a few of these lately this will be visable when you drop the fittings.

or fault with one of the spots, failing that as the other guys say you could be looking at rodent damage and as its a flat roof lets hope its not.

good luck

i always check in the switch first aswell before i go dismantling the spots you never know your luck.

 

[SPECIAL LOCATION]

Thought #5! :Blushing

Or maybe a poor terminated cable where either L or N have been nicked or partially cut with knife or cutters....

Cable aged a bit.. PVC gone a bit brittle/harder/less supple...

so crack in insulation opened up more allowing bridging across to earth..

but not direct good low resistance connection?

now back to option #3

GuinnessGuinnessGuinnessGuinnessGuinness

 

[batty]

We need to open a book on this one my bet is cables burnt on a fitting.

 

[mikep]

Carry out insulation test see what that gives you, pull down a lamp divide the circuit and switch on, no trip then connect part of the disconected section see if that trips carry on and narrow it down till you know the section causing it.

Had a ring doing that once only every few days, turned out to be a floor board nail through the T+E, only happened when they walked to the corner of the kitchen to use the washing machine.

Cheers, Mike.

 

[bengie]

i bet loose connection on fitting that has burnt cables which are shorting out.

 

[kme]

Wellllll.....

If we`re on bets for the fault (unseen) ; I`ll go rodent(s). There`s quite a resistance across the fur of an old, dried out bit of vermin

 

[Doc Hudson]

Wellllll.....If we`re on bets for the fault (unseen) ; I`ll go rodent(s). There`s quite a resistance across the fur of an old, dried out bit of vermin

If the forum is running bets again, I had better check with Admin that the gambling licence is up to date. I have to ask, rodent fur resistance, is this something you have actually measured yourself KME, or just acquired knowledge?

Doc H.

 

[wozz]

If the forum is running bets again, I had better check with Admin that the gambling licence is up to date. I have to ask, rodent fur resistance, is this something you have actually measured yourself KME, or just acquired knowledge?Doc H.

see if SPECS can test himself!

 

[Doc Hudson]

Maybe Apache has some useful clamps and probes that could be inserted for the measurement?

Doc H.