On Sat, 15 Dec 2012 18:29:14 +0000, Colin Stamp
wrote:

I wouldn't mind betting that the leakage that's causing your trips is
coming from a single source. It may or may not be over 30ma, and it may
be highly intermittent, but finding that slightly duff appliance would
be a better bet than replacing the RCD for stopping the trips. A new RCD
may well be very nearly as sensitive as the one you have already.

It's possible, but after a few years of trying to find the problem (it
only trips very occasionally) I'm willing to risk GBP 30 or so on a
new RCD just to eliminate that.

One thing that tends to implicate the RCD is that the house is only
around ten years old, and my next door neighbour also has problems
with the RCD tripping. I expect the builders used the cheapest things
they could get hold of.

If it was my system, I'd be trying to measure the actual leakage current
so I could go around plugging things in one-by-one, hoping to see a
significant increase at some point.

I've done that. I've meggered (can you use that as a verb?) all the
equipment between L+N (shorted together) and E. No problems found. But
this only measures the insulation resistance, so...

I broke the erath wire out of an extension lead, cut it and then ran
all the equipment through that, using a multimeter on AC mA to measure
earth leakage current. No problems found - nothing above around 100 uA
IIRC.

I wonder about things like the fridge, which is on a thermostat and
maybe has a defrost heater that comes on occasionally. That's
difficult to measure.

I guess I could megger the fixed wiring, but it seems like clutching
at straws.

Since you don't seem to mind fiddling about a bit, you could temporarily
connect a multimeter to the current sensing coil and then characterise
the reading you get against your leakage plugs.

That's possible. Once I've got the new RCD in, I might play about with
the old one to see if I can convert it into an earth leakage
measurement device.

On the other hand, you could just replace your kettle. It always turns
out to be that in the end ;o)

Not as easy as that I'm afraid. I've checked the kettle earth leakage.

While this has been going on, I've had a few genuine earth leakage
problems which have been found and fixed. One was the iron, and the
other the oven element. But the underlying nusience trips remain.

Cheers,

Colin.