"Why does the oven keep tripping the earth trip? It's so annoying. Can you sort it out?"
Editor's Note: Click here if you missed Part 1 of this two-part series.
Chapter 3: More Investigation
One thing that was curious was that the heritage cable presenting the fault at the distribution board was 2.5mm2 whereas the remainder of the lighting circuit was heritage 1.0mm2. So somewhere on this particular cable circuit was a joint between these two sizes that hadn't presented itself when the recent extension electrics went in. The other curious thing is that the earth fault presented itself at four places:
- At the distribution board in the cupboard
- At the kitchen lighting fittings
- At the lounge lighting fittings
- At a junction box on the lighting circuit on the landing upstairs (the box is tucked away behind a beam and ordinarily invisible).
So the faulty cable had four ends, which meant that there were two hidden T-splices in it!
The inherited electrical installation had not been carried out fully in pursuit of the UK's Wiring Regulations applicable at that time, whereas any professional Electrician is required to leave his/her work compliant with the edition of the Regulations, embraced within British Standard 7671, current at the time of the work. And whereas the work in the extension had been done to BS7671, the installation in the rest of the bothy had presented a lot of inherited faults, all of which had been corrected over time. This one, however, was the last one and a complete pain. The splices had to be found, for Neutral and Earth were still touching at one of them.
BS7671 requires that all cable ends are accessible for maintenance and testing. The two splices and the earth fault were clearly not.
A quick discussion with the Client: "Take the cupboard ceiling out and see if they're in there. It will be easy to hide the repairs when the ceiling goes back."
Plasterboard and glassfibre insulation make such a mess when they come down. Still, keeping the pieces makes sense, and drywall screws and short pieces of batten make a quick and easy solution to putting them back up again, while the saw gaps can be filled relatively easily before sanding down and making good prior to touching-up the paint.
No cables.
"Let me feel around in the ceiling". The Client's hands were somewhat smaller, and their squeezing into tight places discovered a "lego brick" cable connector hidden in the next bay along from the cupboard ceiling. Lo and behold: 2.5mm2 cable on one side and 1.0mm2 on the other. A piece of ceiling outside the cupboard had to come down to get to it to disconnect it, though.
Chapter 4: The Remedy
A 25m reel of replacement lighting circuit cable was purchased. The next step was to pull it in between the light fitting in the hall, which was fed from the other OK heritage cable on the lighting circuit, and the connection point just inside the garage loft space. This is where the extension works lighting cable had arrived from the other end of the house, and the remainder of the heritage lighting circuit cold be fed the other way round. A further two connections onwards to the kitchen and the lounge lights, and then the four-ended cable with two splices could be disconnected and abandoned, thereby bringing the whole bothy up to BS7671 current edition.
Then there was the access problem to consider.
Pulling the new cable in was easier said than done. The space above the hall is covered by a triangular-shaped pitched roof of gentle slope, which had been added above it during the extension works. There wasn't quite enough height to crawl. Further, 200mm of additional glassfibre loft insulation had been added to this space, some of which had to be moved aside to gain access.
"Cup of coffee and a biscuit?" Not now, for goodness' sake!
The space was a pot-holer's paradise, and the tight gap between a rafter and a brick chimney, some 8m away from fresh air, had to be squeezed through in some kind of crazy, itchy, sideways-horizontal limbo dance no fewer than 6 times before the new cable could be connected at both ends. It took an evening's effort just to get it in, and, as any reader that has handled the stuff will know, glassfibre loft insulation is very unforgiving to the human body.
The connections themselves were straightforward, as were removing the temporary supplies set up in Chapter 2. The bothy is now up to standard electrically, there are no more spurious earth trips, and the heritage 4-ended cable with the earth fault is now abandoned for good. All that remains is to tidy-up the ceiling in the hall and the cupboard and make good the decoration, hopefully before any relatives come over for tea and cakes.
Conclusion
The moral of the story is simple: if one is doing electrical work, make sure it is up to current local electrical codes at the time of installation, for it can be a very awkward and annoying job to sort out the problems after the final decoration is done.
The author (PWSlack) would like to thank CR4's Masu for offering advice and encouragement from another continent and for the incredibly kind offer of coming over to help find the fault and fix it, an offer that has not needed to have been taken up.
Postscript
The fault turned out to be a woodscrew, which had been used to screw a bracket to a wall to support a light fitting. There was a cable in the wall that had been buried in filler and remained undetected. The screw happened to have punctured the cable insulation and just kissed the Neutral conductor as it went through. When the light fitting had been added, the bracket became connected to the Earth conductor. Hence the Neutral-to-Earth fault. And as the Client stated, "So annoying."
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Re: Solving an Electrical Fault from 10,000 Miles Away (Part 2)
