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John_BS 4th Aug 2020 11:54 am

RCD nuisance tripping and other problems?
I friend has had intermittent tripping of his consumer-unit master RCD, so in an attempt to trace the problem, he bought one of these clamps.

They are available under various brand-names, but clearly come from the same source in the far east. I bought a ProPower-badged example from CPC, which seems to be a good deal.

It measured 30mA @50Hz pretty much spot-on, and is certainly much better than the 5% spec. I then checked its frequency response, which seems to be flat to around 2kHz, with a gentle roll-off above that.

So it could also be used for checking e.g. loudspeaker impedance while still in circuit, using say 400Hz or 1kHz tone.
The only thing to watch is that it's susceptible to stray magnetic fields, so will read several mA if too close to the Weller transformer!


Skywave 9th Aug 2020 10:04 pm

Re: RCD nuisance tripping and other problems?
Interesting device by the sound of it.

I had similar trouble about one year ago. So I did a routine PAT test with the 'yellow hand-held' on all items connected to that ring. (I do that throughout the house every 12 months as a matter of routine.) The kettle in the kitchen looked highly suspect. :-/ Then I remembered the symptoms. Often - but not always - the RCD would trip during the night - sometimes when I was asleep; sometimes when I was awake. (I am a dedicated 'owl' :o ). Whenever I go to bed, I make myself a nightcap - usually 'Horlicks' substitute. But during the day, the kettle gets a lot more regular use: it's empty, refill (enough for two cups plus a bit), boil; make drinks; kettle then empty, or very little water remaining in it. Repeat sequence as required. But overnight there was plenty of undisturbed time for water leakage through to the mains connector and only one drink had been made: much more water left in the kettle. (It was an old 'Swan' kettle.) Replacement of that aged kettle solved the problem.


Refugee 10th Aug 2020 12:07 am

Re: RCD nuisance tripping and other problems?
Electric kettles used to be very bad for that.
We were given a Molinex one in the late 1980s that used to leave a little spot of water on the work surface. They were quite common in the day but absolutely no photos on the web now. There were no digital cameras and RCCDs were still rare.

I was woken in the middle of the night and then heard a loud bang. I resigned myself to having to repair something in the morning and just as I was going back to sleep again there was another bang. I got up on the grounds that something had to be done about it as it had not crowbarred the fuse out.
I could smell it in the kitchen so that was the room that got all the plugs pulled.
It was the next evening when I started with the kettle as a suspect and found that the window had a little drain hole at the bottom indicating that it was a problem known to the manufacturer.
When shopping for a new one in one of the big appliance sheds that still trades to this day I spotted a cordless one in the same style including the little drain hole8-o8-o8-o

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