Most difficult fault

[Judd]

Just wanted to know out of curiosity difficult wiring faults people have come across in there careers? what type of fault, and how you got to the bottom of it,
Some faults are easier to find than other, maybe the fault was an emergency call out or perhaps something that was picked up on a EICR,
I came across and neutral to earth fault that threw me a bit the other day,
Look forward to hearing your replies.
Lou

 

[NDG Elecs]

Worst I had, in terms of being unfathomable for several months, was a cable being crushed causing what I decided to call a 'pressure' fault. This caused intermittent RCD tripping, usually after warm and sunny weather (should have known it was a dead loss there and then!!).

I only found the fault after around the fourth visit, and this was partly due to the fact I was clutching at straws by this point. All test results were consistently clear the three times I tested the 3-4 circuits possibly at fault.

The fault was found / presumed to be a cable leaving a FCU and going through the side of the window frame to feed an exterior light. I say presumed, because after I have rerouted the cable the tripping did not recur! Plus the cable section I think was causing the problem still tested all good, whacked 1000V through it after I dissed it and still got perfect readings.

Basically they have a set of brown uPVC windows and doors in a straight run across their porch. In hot weather they expanded quite a bit causing the frame to crush against the cable. It only entered my head that this could be a possible cause as the owner said that when it was really hot they couldn't even open the door and had to go in and out through the back.

The 'faulty' cable was completely buried in the wall and was not visible at any point. It was just sheer chance that I knocked on at the property on a warm and sunny afternoon and she couldn't open the door, which then got me thinking!!

 

[DC-backfrom the past]

Hi Judd
the most confusing fault I had was about 17 years ago, a friend who mentioned his wife was getting electric shocks from their metal sink. No one else got any shocks. I went out to the house presuming that it was an line to earth fault and due to bonding made the sink live.
I checked the sink and there was nothing and then checked all the circuits nothing at all.
I asked how often this happened and she said it only after 1 am after her backshift. She was a nurse and they thought it was static electricity problem.
Within the cupboard the consumer unit was housed. I saw a small sliding door, behind this was two time clocks for white meter heating complete with isolator and fuse box.
The heaters had been removed years previously with no obvious signs that they had existed anywhere in the house.
The clocks clicked on at 1am for white meter heating. I checked this circuit and the sink was indeed live .
My mate had got new windows fitted and a nail had gone through a cable which had been for this heating within the wall.
The nail had caused the live and earth to short causing the sink to become live.
Whoever had removed the heaters had taken the switches off and left the cables in terminal blocks and papered over the blank plates.
They hadn't switched off or removed the main fuse thus live cables were within the walls during the night.
Because the time clocks were behind a sliding panel in the hall cupboard my mate didn't know they existed.
His wife had had been getting the shocks for about year however not every backshift. we reckoned that on each occasion there was minutes in it. she would use the sink maybe just before 1am and some nights just after.
just goes to show people put up with things because they think its static or its only a flickering light .....what's the harm?

 

[Des 56]

Interesting faults posted,I will try and put a little flesh on my own story
Did the wiring for a Bathroom refurb,Bungalow for a old woman
About 18 months later the builder asked me to have a look because nuisance tripping was reported

The fault was intermittent,so off to a good start
Insulation test was fine,Rcd holding no problem,switched on all lights and Rcd tripped after a few minuts,re tested insulation resistance and the readings were very low on the one and only lighting circuit,at least the problem circuit was identified
Started sectioning off the circuit and sods law the values improved no end,faults had disappeared

Back to square one,so put lights back on and a little later off goes the Rcd and readings poor once again
Started stripping down each light,typical that when I got to the last light in the old womans bedroom I found the fault
Removed part of the fitting,a metal bowl that housed the connections to the lamps,it was full of Maggots and a goo which was possibly maggot crap (they tipped all over the bed when I dropped the bowl down)
I got up the attic and the stink hit me,rotted flesh
Had a look above the culprit light and about a foot away was what was left of a Rat that had been poisoned
My conclusion was the Maggots would dine on the Rat,when the light was lit it gets warm enough to attract the critters into that light fitting,when it tripped and cooled off they would make their way back to the dinner table

 

[KEV 1 N]

My mother in law and her ex partner had built one of those wooden DIY log cabin houses (several years before I met my wife) anyway they got fed up with each other and split up after living in there a couple of years..blah blah, so the house was rented out...long story -short, the tenants were getting tingles of the metal light switches, so I was asked to have a look. Took the switch off....cpc cut out of T&E, took another off...same again...took a light down, again cpc cut out?? Checked DB, lighting circuit cpcs cut out!! WTF! Apparently the house was wired by an electrician who also apparently wired some other self build properties in the same area! So all lighting cpcs were cut out, and the live tail at the main switch hadn't been tightened, so it was burnt....oh and no rcds on anything!
Anyway I managed to pull length on most items and reinstate the earth, only two wall lights where he must have had a concealed joint, which I couldn't earth, so just had to put double insulated fittings up.
I don't know what the hell this guy was thinking cutting every cpc out of the T&E!

 

[dmxtothemax]

Any one still want to be an Electrician ?

 

[DPG]

Anyway I managed to pull length

I've never pulled length on a job before. Well, maybe the odd time

 

[DPG]

I apologise for my juvenile post. I've let myself down and I've let all of you down.

 

[KEV 1 N]

I apologise for my juvenile post. I've let myself down and I've let all of you down.

There's always one!

 

[Bob Geldoff1234]

Many years ago we were called out to a fault on a fire alarm system in an old person's home.The alarm would go off in the middle of the night but when we got to it every morning there would be no faults present and all the cables always tested fine.
We started asking questions and found out that in general the alarm went off around 3am in the morning.We got the staff to ask around the residents if anything happened at this time.One old lady said she got up to go to the bathroom at approx 3am every night.
It turned out that someone had nailed a board down and the nail was just above the cable.As the old dear swung her legs down to stand up,she stood on the board which shorted out the cable and set the alarm off.Of course as she stepped off the board the nail came back up,hence clearing the fault!
I always instill into apprentices that the best form of fault finding is to ask questions first.Quite often the customer will tell you where the fault is without even getting your tools out!

 

[Jacob atkin]

Had a bad IR reading on a 16a 240v commando socket outlet, disconnected the cable and it tested fine and the socket outlet tested fine. Tested the breaker and it tested fine but as soon as everything was reconnected back to the bad reading. Re-terminated everything and still a bad IR reading. Told the other spark at shift change and he spent ages doing the same as me but couldn't get his head round it. I'm back on shift the next day and think I will have another go, tested it all again several times and just couldn't get my head round it. Went for a cup of tea and a smoke and by the time I got back the fault had disappeared. Every month when I get back onboard the vessel I test it and it has just disappeared.

Just can't get my head around this one and why it disappeared

 

[Judd]

Thanks for everyone's comments so far I've enjoyed reading all of your stories,
Judd

 

[loz]

my own house. 15 years old and not touched since built on an estate.
I put some extra sockets in, extended ring etc. took a quick ring continuity neutral and earth all good. nothing on the live. traced it to inbetween 2 sockets. looked at the skirting and noticed a nail below the socket, so thought I'd give the cable a little tug and hey Presto. either it wasn't tested upon completion by sparks ( local cowboys) or it was tested before skirting were fitted

also ha phantom faults with seem to disappear and reappear. funny old game we work in.

 

[GlenTavener]

Many years ago now rewired a large country house, or two men who worked for me did, one an electrician one an apprentice. Final tests all good and then later the intermittent RCD tripping started. Sent the electrician there, test all OK, but the tripping continues. Eventually went there with the guy who wired it to get to the bottom of the fault, eventually got him walking around the house, a lot of floor space, and finally it trips. So now we know the area. tracked it down to a ring main in one of the sons bedrooms. Break the ring down and discover the leg where the problem is, floor boards up and find that leg was pulled through the floor over a steel girder. Space enough but not with a twist in the cable. I say nothing then, pull in a new cable make good and go. As we drive back my man says I remember now that cable was tight to pull in. He was somewhat elated that we finally found the fault, that was until I pointed out that his lack of workmanship had cost us a morning in time and him several visits previously, and that it would affect his bonus which I usually paid for good work. The son was only home on random holidays from boarding school so for the most part no one used the room. Many years ago now, I no longer employ anyone - sheer bliss.

 

[Squid]

I always instill into apprentices that the best form of fault finding is to ask questions first.Quite often the customer will tell you where the fault is without even getting your tools out!

Totally agree with that statement as that is about 90% of the work done to find the fault.

 

[Des 56]

Deviating slightly off thread because this one was extra easy to find

Very large bedroom which had 2 sockets on each of 3 walls
A young just out of his time chippy then fitted his skirting board

With a ring fault narrowed down to this bedroom,I wonder where he got the idea that right smack below the sockets was the best place to drill and screw

Only 6 fixings he made,yet he scored a bullseye on three socket cables
He's probably still out there playing his game of darts because I didn't get the chance to meet and throttle him

 

[Octopus]

About 6 years ago I had a client with irregular nuisance tripping - up front 30ma RCD, so the whole lot went off. This was a 16th century cottage with 3 extensions done by bob the builder.... or Stevis Wonder!

There appeared to be no pattern to the tripping, except the client thought that "snow" was a common dominator.

Over Xmas things went from bad to worse and they struggled to cook xmas lunch

So they asked what would help them - RCBO board - so that was fitted a couple of weeks later ...... so now only 1 circuit would go off.

Sure enough a couple of weeks later they called me to say the kitchen lights were the "issue" - but not on switch on ..... irregular but some time later

IR this area, removed lights ........ they had 3 x lights with multiple GU10's on a vertical poles fixed to the ceiling..... removed each in turn and discoverd that one of them had "rust" markings at the top GU10 ............... was it condensation from cooking? a leaky roof?

They decided they could do without the missing fitting of the 3 and the circuit never tripped again.

Fortunately for me the client was understanding, patient, and had money ........

I continue to work in said house now, for the new owners.......

 

[ipf]

Had a bad IR reading on a 16a 240v commando socket outlet, disconnected the cable and it tested fine and the socket outlet tested fine. Tested the breaker and it tested fine but as soon as everything was reconnected back to the bad reading. Re-terminated everything and still a bad IR reading. Told the other spark at shift change and he spent ages doing the same as me but couldn't get his head round it. I'm back on shift the next day and think I will have another go, tested it all again several times and just couldn't get my head round it. Went for a cup of tea and a smoke and by the time I got back the fault had disappeared. Every month when I get back onboard the vessel I test it and it has just disappeared.

Just can't get my head around this one and why it disappeared

Was that vessel the Marie Celeste, by any chance?

 

[ipf]

my own house. 15 years old and not touched since built on an estate.
I put some extra sockets in, extended ring etc. took a quick ring continuity neutral and earth all good. nothing on the live. traced it to inbetween 2 sockets. looked at the skirting and noticed a nail below the socket, so thought I'd give the cable a little tug and hey Presto. either it wasn't tested upon completion by sparks ( local cowboys) or it was tested before skirting were fitted

also ha phantom faults with seem to disappear and reappear. funny old game we work in.

Intermittent faults you mean?

 

[brianmoooore]

Customer reported very intermittent RCD tripping, which would trip again if immediately reset, but after a couple of minutes would be fine.
It only happened during the day, and of course, IR testing produced no clues.
Several visits later, I got lucky while there doing some other work, and the RCD tripped. Quick IR test showed a rapidly disappearing E-N leak on a RFC serving the utility room and garage.
Culprit turned out to be a large chest freezer in the back of the garage with a light built into the lid. Ice had built up in the enclosed bulb compartment, and when the lid was lifted, bulb was switched on, and would melt a little of the ice. The resulting water was running down into the bulb's base when the lid was closed, sometimes causing a E -N leak sufficient to trip the RCD, but of course, with the bulb off again, the water rapidly turned back into insulating ice, destroying the evidence.
All that was required to effect a cure was a quick defrost of the offending lamp compartment.
Because of it only rarely happening, and the several minute delay between the freezer being opened and closed, the customer had failed to make any connection between opening the freezer and the tripping.