Residual Current Blues (by alaric)
Bah. Yesterday the RCD tripped, shutting off the electricity supply to the house, while I was standing in the kitchen.
This means that, somewhere, something's leaking electricity. An RCD measures the current that goes out to appliances on the Live wire, and measures the current that comes back via the Neutral wire, and if they differ by more than about 100mA (in the case of our unit), then it knows that coulombs of charge are going awry somewhere - which is usually a dangerous situation, since it means either a short to ground of some kind (which can start fires due to electricity flowing through things it shouldn't and making them hot) or a short to ground via a human being, which is usually rather unhealthy.
So I proceeded to the meter cupboard and tried to reset the RCD, but it wouldn't go; whatever was leaking current was continuing to do so, rather than it being a one-off event (I've had experience of RCDs being tripped by noise smoothing power supplies that dump noise signals to earth rather than neutral).
So I opened the fuse box, pulled the first fuse (lighting circuit), and tried again. Still no joy, so the problem wasn't in the lights. Neither, it turned out, was the problem in the circuit that fed my office, the tumble drier, and the washing machine.
Which left three options: the water heater / shower circuit (which also happens to feed my wireless access point and a router, due to the airing cupboard being the only place they can plug in, thanks to network cable lengths), the cooker / fridge freezer circuit, or... the ring main that fed the entire house's normal sockets, apart from the office. Well, at least I presume it's a ring main. It might not be. The original wiring is quite old.
Funnily enough, things seemed to run fine without the ring main up. Oddly, however, when I only had the cooker circuit disconnected, it seemed to be fine until I switched off at the fuse box (in order to swap fuses), at which point the RCD tripped. I can think of reasons for this, but they all seem unlikely. But without the ring main live, the RCD seemed stable.
So I went around and turned everything on the ring main off, put the fuse back in, and powered up. Then went around switching things on, waiting for the lights to go out as the RCD tripped again.
But it didn't trip. Whatever was wrong has fixed itself. Which is bad because it means that the real problem is still there, lurking somewhere in my house. And also bad since it meant we were up until 3am in the end dealing with everything, and had trouble sorting out dinner with no ring main, plugging the kettle into the cooker outlet which wasn't very conveniently placed for a kettle with a short lead.
Alaric, Building Maintenance | alaric | 
Thu 19th Oct 2006 4:33 pm
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