What is the hardest fault you have ever had to find?

[Top Cat]

Thought i would start with one i had 30 years ago!

Office block, loads of fluorescent's etc all the ground floor not working, rewireable fuse.

Fuse wire disintegrated so fault not overload.

Meggered everything, clear L-E, N-E. but picking up control gear for L-N.

Thought i would try just putting new fuse wire in! Tried it and everything worked OK.

Three weeks later same call.

Thought i better do it properly this time so took down all flo's, checked gear inside, disconnected gear. Meggered again, no fault apart from L-N.

Checked with staff to see if any other rooms. Oh yes , a store cupboard.

Found an enclosed light fitting with 100 W lamp in it. It was the sort with the aluminium "pie dish" reflector. I found that it had chock block connectors behind it that had half melted to the earthed pie dish.

Turns out they hardly use the store cupboard and if someone left light on for more than 15 minuets the chock block would get hot, melt against pie dish and blow fuse, then as it cooled the plastic would retract and hey presto no fault!

 

[Richard]

Had a nasty borrowed neutral fault before.

Basically, main neutral feeding a main kitchen DB had D/C'ed due to loose connection in main Isolator. A borrowed neutral (from a different D/B) on the 4 story stairwell lights ment that the kitchen D/B still had a path to neutral - Via all the light fittings which were wired in 1.5mm T+E. So that was a whole commercial kitchen through a 1.5mm neutral! The cable had melted along it's whole length. Modern type of building too so took ages to sort!

 

[johnboy6083]

Once had low IR l-n on a ring that we had rewired. Unscrewed sockets from the walls, all connections good, no nicked cables, and no copper showing. Eventually we found that one of the sockets was faulty.

Also had one on Friday, where the water board control room told me that according to their telemetry, the genny was on fire. The system is PLC controlled, but I have no access to the software, and the drawings are wrong, as the "as built" drawings are not yet finished. I spent ages tracing all of the cables, manually testing PLC inputs with a fly lead, whilst on the phone to control. It eventually turned out to be a relay that had no input to energise the coil, which in turn gave the PLC inputs. A quick modification, and jobs a good un

 

[sedgy34]

HEY T, C
few years back did 30 apartments and had in 1 apartment a ring circuit with 3 screws in it differnt legs of the ring done my sweed in found 1 screw dont expect to find 3.
recently fitted some fans nuaire genie x, they stay on boost and dont revert to trickle had to fit a resistor to stop the inductance from low en lamps in the spots

 

[ipf]

Smacked head on a low 12 inch girder whilst trying to find a fault in a control box on top of a spray booth. That was ******* hard!!

 

[Andyfm]

Had a fault on a ring circuit a few years ago, 3pm on a friday afternoon (typical!) after changing a CU to the a 16th edition with an RCD on the power circuits.
Just before powering up I ran an IR test on all the circuits and found N-E fault on ring, so split the circuit in two then divided up further to pinpoint the fault, it was between two sockets in the kitchen, so removed sockets then found that cables would push up and down in their trapped wire conduits so it wasn`t a nail or a cable caught in the box.
So up came the floor above (chipboard with a fitted carpet on it), and traced the cable between the sockets but noticed at one point the cable dropped down through the ceiling, looked below and there was a fitted cupboard about 20 years old but no sign of any electrics. I explained to the chap that there was a problem so he agreed to remove the back of this fitted cupboard and there it was , a single socket which had been hidden for 20 years and on removing the socket front found the screw had caught the neutral and had been like it since it was fitted probably 25-30 years ago - Got home about 9pm after putting the house back together !!

 

[nickblake]

Beaumaris castle walk way lights kept tripping the breaker switch it on and i could work for a year then trip with a bang , insulation always was a tad lower than normal due to the moist area's which the lights were installed had an RCD on them so pretty well protected , with the castle all the cables were embeded into the joints of the stone work so they couldnt be seen not a way i would have done it but when you are restricted by cadw then you had to do what they wanted couldnt drill into the stone etc , the fault eventually raised its head bang then switched on worked , eventually found a blow cable you could here a very faint fizzing comming from one of the walls the cable had burnt out always very wet then but when you have almost a mile of corridors dripping with water splitting and testing between points the public passing every 5 minuits narrow corridors it was fun mind

 

[Guest123]

Maybe not the hardest fault to find but, trying to convince the customer that IT IS their appliance that's faulty and not the nice new DB you have just fitted.:indian_chief:

 

[nickblake]

had one just like that came on the phone ranting and raving as they do went back found that hubby had put a new plug top on a lamp and wired the neutral to the earth terminal lol what a muppet

 

[benji]

stood in for a spark on his holidays brand new process plant all in pyro and finished just req.testing & commissioning ,all went well till no live comming back from limit switch ?somebody had opened cover on switch pulled insulation back on one core and cut section out of core then pushed insulation back

 

[telectrix]

had a purler with an alarm system. PIR was fitted in the corner of a L shaped lounge, this corner being outside wall in the SE corner of the house. 3 days running, around 8.am the alarm activated . log showed it to be this PIR. sun up through the east facing window, reflected off a glass coffeee table to a mirror in back of china cabinet, and back towards window and also at PIR. double knock selection on zone cured problem.

 

[Knobhead]

A control circuit for a solenoid valve that would intermittently fail at night only. After a while it would just start working again. It wasn’t just me, it was driving the other shift lads nuts as well.
I put a couple of relays and a lamp in to latch if the PLC output failed, it never did but the valve kept failing. Change the valve? We’d got a stack of valves we’d changed. Cables all checked out perfectly.
This went on for near three months and then the problem just vanished. Nine months later we were back where we started, back came the fault. at least this tied it down to cold winter nights.
To cut a long story short. With the wind in the right direction the air in the line froze, once the air stopped flowing the pipe would thaw with the heat of the machine.
Amazing what a bit of heat tape can do, no more problems.

 

[plugsandsparks]

Probably the longest running series of faults was on a very large house with lots of external circuirts fed from the garage all going back to a CU with one RCD.
Client complaining of lots of tripping.
First time it was the pond lights.
Recommended replace CU in garage and move garage cct off RCD in house.
Went quiet then house tripping again.
This time it was the iron - iron replaced.
Got called out when freezer went off again.
Thought right i am taking this lot apart, so IR all ccts, perfect, checked each cct for earth leakage, all rubbish and readings all over the place, no consistent readings from RCD tester when bringing in ccts one by one, was really doing my head in. So disconnected everything again and notice on cct for the kitchen ramped earlier than the rest, thought right off to the kitchen.
Anyway after a few hours with my head stuck in lower cupboards discovered a cable joint box (very small white one) extending the cable for the dishwasher, thought that looks small for a dishwasher, opened it up and could see visible tracking of current live to earth inside joint and it was located just under the flexy hoses for the taps - nice.
Replaced and re-routed it and it made a difference but not as much as i would have liked.
Ended up totally gutting the CU and rebuilding it using MG RCBOs, got 4 of them in to spread all the leakage from all the electronic gear that had mounted up, and one RCD for the rest. Since then all piece and quiet.

 

[Top Cat]

Got called to a house because of nuisance tripping. TT system 1 30ma rcd controlling everything.

Meggered all circuits (6) and all had readings of about 1.5 -2.5 megs. Advised customer to have new board with RCBO'S.

He agreed so fitted new board and he paid me.

Next day he said all RCBO's have tripped at the same time.

Went round checked everything could not find anything wrong so started to think what could make 6 RCBO's all trip at the same time and so thought i would check the overhead supply.

Then i saw it, the neutral joint on the pole was half burnt off. Called DNO and they put it right within the hour!

Trouble was the guy stopped my cheque because he said nothing was wrong with his original C/U.

i told him that he should still keep the new C/U because with the low readings and only 1 RCD he could still have problems.

No, he made me take out new C/U and refit old one. For nearly 2 days work he only paid me for my original call out fee!

 

[Knobhead]

One has just come to mind.
An intermittent earth fault on a 2.6MW earth free system. It took me three months to find.
When I found the fault I wished I hadn’t. The fault was on the induction coil of an iron furnace, I found molten iron squirting out of a crack in the furnace. It takes months for iron to work through the lining, so the odd little dribble would cause the fault. I now found myself underneath 100 tonnes of molten iron burning it’s way out.
PANIC!
It wasn’t only me in panic mode, is a “clutch” of managers/directors in headless chicken mode the right term? The entire works was shut down for a week for us to do the repairs.