lighting fault

[ultinator]

hi all,

having a bit of a blonde day today.

so here's a brief summary of the situation...

bungalow...
nothing new installed recntly...
old lady said lights tripped and wont go back on....
arrived and she demonstrated a few times that the breaker just trips, which i explained really isn't either advisable or necessary.
RCD was holding.....
was suprised at the heights of the fittings. between 4-5 metres high. so now had a lack of access as an issue....
without being able to remove all bulbs i done IR between L+N - E and got 0.00 Mohms.
then checked switches and d/c feeds to lights and no change...
put some back and the noticed the rcd was tripping now...
said cant do much more at present without access and not sure when can be back as pretty busy...
she looked instantly distressed and explained she is having an op on monday and needs her ensuite lights to work (and the rest) because she will be having to remain in bed and will be suffering some bleeding(dont know what the op is and wasnt gonna ask)
so feeling bad I went and borrowed a vehicle with roof rack, hired a ladder and headed back
started to remove light bulbs and then tested IR and found 0.00 between L and E, with 36ohms of resistance on continuity...(i thought it would be a N-E fault as with all bulb removed the circuit and rcd would hold...but introduce a bulb and turn on and rcd trips)....
so went from points to see if the R1 R2 contuniuity would lessen to show me a direction to head towards....
in the end had to leave a bit early as had been running around all day had no lunch as was trying to hire a ladder which i had to hike down the road to my car from the shop....anyway am going back tomorrow after another morning job....was gonna start splitting the circuit and trying to find the fault..
just really awkard moving a massive A-frame ladder around this bungalow which is really low in places and ridiculously high in others and there is literally no access above these lights is the roof...
any time saving ideas about this 36ohm resistance between L-E?
I felt like a zombie today so tomorrow should be much more productive

you may Fire your criticism at me now

 

[RyanCheetham]

Is there a tv splitter/amplifier taken from the lights?

 

[tony mc]

What was the N to E and L to N reading when you tested are you sure nothing is still connected Fan TV amp etc !

 

[Tiny Spark]

I would say the resistance is to high to be a direct short (Otherwise it would mean approx 1500m of cable if my calcs are correct!) so I would say its a restricted short such as a burnt out cable, rat nibbles etc.

Easiest way to find it is to split the circuit in 2 and keep halfing it until you find the problem.

 

[Octopus]

Has it been raining or has she got rodents? or an extractor fan or TV amp?

 

[Richard Burns]

If the initial fault was the MCB tripping and not the RCD then there is a L-N short somewhere, this does not seem to have been found yet.

Once you had looked at the switches you have now got a fault to earth to trip the RCD. This is very likely to be found at the switches as that is all you had changed, insulation scraped off, trapped cables etc.
This fault which is showing your 36 ohms to earth, this equates to a 1400W load so unlikely to be a piece of equipment, although electronics can give odd readings. Are there any lighting transformers about?

The second fault will mask the first as the RCD will trip more quickly (unless it is a dead short L-N).

The with no load, no trip : some load, RCD trips sounds like a borrowed neutral, worth checking you rewired upstairs downstairs switches the right way round.

I would tend toward the original fault being a low level light fitting damaging the supply cable until it shorts. L-N faults only are not likely on T&E cable. High level fitting are rarely disturbed.

 

[tony mc]

I would say the resistance is to high to be a direct short (Otherwise it would mean approx 1500m of cable if my calcs are correct!) so I would say its a restricted short such as a burnt out cable, rat nibbles etc.

Easiest way to find it is to split the circuit in 2 and keep halfing it until you find the problem.

What size CSA are you doing your maths with out of interest as its a bit high unless your using 1.5 singles!

 

[Tiny Spark]

1.5mm at 18mOhms per Meter.
Problems with the lighting cct so ime making a assumption its either 1mm or 1.5mm.

 

[worzol99]

So you left an old lady without any lights because you had no lunch!!

Very Professional of you

 

[sledgehammer]

I had a cracking lunch, and a ladder and a massive pair of steps on my van all day. And thats where they stayed all day. Typical.

 

[ayjay]

just split the circuit in half simple

 

[ackbarthestar]

nothing new installed recntly...
old lady said lights tripped and wont go back on....
arrived and she demonstrated a few times that the breaker just trips, which i explained really isn't either advisable or necessary.
RCD was holding.....

Original Fault 1

was suprised at the heights of the fittings. between 4-5 metres high. so now had a lack of access as an issue....
without being able to remove all bulbs i done IR between L+N - E and got 0.00 Mohms.
then checked switches and d/c feeds to lights and no change...
put some back and the noticed the rcd was tripping now...

New fault 2

said cant do much more at present without access and not sure when can be back as pretty busy...
she looked instantly distressed and explained she is having an op on monday and needs her ensuite lights to work (and the rest) because she will be having to remain in bed and will be suffering some bleeding(dont know what the op is and wasnt gonna ask)
so feeling bad I went and borrowed a vehicle with roof rack, hired a ladder and headed back

started to remove light bulbs and then tested IR and found 0.00 between L and E, with 36ohms of resistance on continuity...(i thought it would be a N-E fault as with all bulb removed the circuit and rcd would hold...but introduce a bulb and turn on and rcd trips)....
so went from points to see if the R1 R2 contuniuity would lessen to show me a direction to head towards....

Part of the new fault 2

in the end had to leave a bit early as had been running around all day had no lunch as was trying to hire a ladder which i had to hike down the road to my car from the shop....anyway am going back tomorrow after another morning job....was gonna start splitting the circuit and trying to find the fault..
just really awkard moving a massive A-frame ladder around this bungalow which is really low in places and ridiculously high in others and there is literally no access above these lights is the roof...
any time saving ideas about this 36ohm resistance between L-E?
I felt like a zombie today so tomorrow should be much more productive

Recheck your terminations at the switches
Then check the condition of the terminations at the lights
Then if still in a pickle half the cct at the lights and IR each way

 

[nickblake]

check the light fittings don't have burnt out cables at the lamp holders most common cause of what you have described

 

[ultinator]

thanks to all, i wrote a lengthy response specific to most replies but it hasnt appeared.

its a bungalow, so crossed neutrals is unlikely. no switches control lights on both circuits. another lighting circuit still functions, on a separate RCD, and the switches went back as previously wired. have removed majority of fittings, will remove the rest asap. will split the circuit and check from there after a visual... the high ceilings and limited floor space really are a pain in the arse with the a-frame i have, which is frustratingly time consuming moving about. dont have time to go back for a while so need to wrap it up...possibly run a temporary supply to power lighting in her bedroom and en-suite or hand over to someone else depends what the lady wants..
And maybe it sounds bad to leave early due to no lunch, but i would be back within 18 hours of leaving her house in a no worse state than it was, and she has many plug in lamps for light...she was understanding enough..i was running all over the shop to try and finish in one day...but by the time of swapping vehicles and hiring a ladder and going back i didnt have much time...its not an ideal situation but it not always is...

 

[coldyron]

Any access to the loft? Had something similar yesterday and narrowed it down to a cable running from the switch to a light which had been scored either at installation or by a rodent.

Luckily I'm on a diet so was able to solve the fault before eating :devilish: