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To be useful on an RCD-protected circuit, it would obviously have to either have a back-up battery or a non-volatile memory, but that's no problem. Such a device could probably quite easily be produced by poaching from RCD technology and electronics, and I'm sure could be fitted into a plug-in unit, and need not be particularly expensive. A more sophisticated version might store 'continuous' results in semiconductor memory (as you say, the sampling frequency would need to be pretty high), but that would really not be necessary (or necessarily useful) for simple 'culprit identification' purposes.
Kind Regards, John
Given the extent of difficulties (and time consumed) seemingly often involved in detecting the source of nuisance RCD trips, I'm rather surprised that we do not see (or do not see being used) 'leakage' monitors - or, at least, detectors. I'm sure, for example, that it would be easy enough to produce a relatively cheap plug-in device with a few LEDs which indicated whether L-N imbalance has exceeded certain levels (say 1, 5, 10, 20, 30, 50mA) during the period it had been in circuit. If the OP's electrician had such a device, a definitive answer about the appliance concerned could be achieved very easily. Do any such devices exist?
I don't see why it would have to be on a non-protected circuit. On the contrary, one would normally want to use it on an RCD-protected circuit, to ascertain whether a particular appliance had resulted in an RCD trip. Nor (in its simple form) would it need any continuous recording such as you describe. As I said before, it would be adequate to have a relatively cheap plug-in device with a few LEDs which indicated whether L-N imbalance has exceeded certain levels (say 1, 5, 10, 20, 30, 50mA) during the period it had been in circuit.I would agree a residual current monitor (RCM) with recording would be a good tool but I also see some problems. First it would need to be on a non protected circuit and second would need a chart recorder not an every x seconds and join dots like used with current and voltage.
To be useful on an RCD-protected circuit, it would obviously have to either have a back-up battery or a non-volatile memory, but that's no problem. Such a device could probably quite easily be produced by poaching from RCD technology and electronics, and I'm sure could be fitted into a plug-in unit, and need not be particularly expensive. A more sophisticated version might store 'continuous' results in semiconductor memory (as you say, the sampling frequency would need to be pretty high), but that would really not be necessary (or necessarily useful) for simple 'culprit identification' purposes.
Kind Regards, John