On 15/12/2012 19:06, Caecilius wrote:
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.
It might be interesting to see what happens, assuming you can get a
significantly less sensitive RCD but, even if the trips stop, I reckon
something somewhere will still be occasionally leaking abnormally.
Still, as you say, it'll give you a spare RCD to play with.
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 don't think you've got everything covered with those tests. The Megger
doesn't allow the appliances to be powered, so many potential leaks
won't have a chance to occur during the test. Also, leakage current
doesn't always come back through the earth wire of the leaking
appliance. The beauty of using an RCD to measure the leakage is that
you'll end-up getting a proper RCD's-eye view of the imbalance between
live and neutral currents with the appliance running.
Having said all that, I'd put money on the fault being highly
intermittent and difficult create whilst you're watching for it.
(
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.
They can be tricky buggers. One gave me the runaround for over a year,
tripping the RCD in the middle of the night once every few months and
then playing all innocent the following day. It turned out the tiny
water leak into the handle only became a problem if it was left nearly
full for many hours.
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.
I feel for you. These problems can be soooo frustrating. If you get
*really* desperate, perhaps you could arrange an independently RCDd
supply that could be used to power strong suspects long-term whilst
waiting for the next trip.
Cheers,
Colin.