Hello,
I’d be grateful for some advice on a tricky job.
Got an evening call out to a house where the power had gone off, the RCD kept tripping.
Arrived, checked, it was an old-fashioned fuse board with six circuits, two 30 amp rings, upstairs and downstairs, two 5 amp lighting circuits, up and down, a 16-amp combi boiler and a 40-amp shower fuse. The RCD had been installed at some time on the tails between the meter and board to cover the fuses.
As I investigated, I found some problems. I opened up all the ground floor sockets, most of them were OK, wired correctly, LL, NN, EE, but a switch for an outside light had been wired directly from a socket without a fused spur, I disconnected it. I also found a double socket spur that had been wired directly from the cooker control switch; the neutral terminal inside the double socket had melted, so I disconnected that and made it redundant. Also found a double socket that had partly melted at the front, replaced that with a new one.
When I switched the board back on (after safe isolation for the work) the RCD tripped again. It was an old one, so I replaced it, but tripping continued. I eventually pulled out the fuse for the downstairs ring, and everything else worked fine. Customers don’t have a downstairs ring circuit for the moment, they are plugging into a 10-meter long four-socket extension running from a socket on the upstairs ring.
That’s the scenario, now I have four questions:
One, I’m going back on Tuesday (earliest I can get back) to do a split-ring IR test, problem is, I’ve been out of work for months due to the lock down, and the calibration on my Fluke MF tester is a few months out of date, that’s why I didn’t take it first time, will the IR tests I do be fairly reliable?
Two, I’ve noticed that the cooker control switch is working, as there is power on the cooker socket, but there is no fuse in the board for the cooker, what might be going on there?
Three, I did a belling out test with a long extension link to establish how the downstairs ring is interconnected, and I noticed that a leg of old red and black cable in a front room socket is linked to a leg of new brown and blue cable in one of the kitchen sockets, i.e. when I put the croc clip of my test cable onto the copper end of the red live in the front room, and the other croc clip of the test cable onto one probe of my Kewtech hand tester, the tester beeped as soon as I touched the other probe onto the copper end of a brown live in the kitchen. so I’m assuming that the old and new cables are linked by a hidden junction box; that might be causing the problem. How can I locate the box?
Four, if I do narrow the fault down to a leg of the circuit, then how can I repair that leg? I ask because it’s an old house, built in the 1940’s, and if, say, a leg of the ring has damaged cable, how do I replace that without tearing out part of the wall and ceiling, causing inconvenience to the customers?
Thank you if you can help.
