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Re: Residual current measurement

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mmm   i suppose you didnt mind getting knowledge from aother people  while
you where learning... then again who wants to know what a 3 year old could
know ??





Re: Residual current measurement
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I had the RCD go out at 7:58AM precisely, once or twice a week,
for months. It actually happened for a month before I realised
that it was always the same time. Then I started leaving things
that have a clock in them unplugged, since whatever it was, it
clearly knew the time of day... no help.

So I started hassling the electricity supplier, since it was
clearly being caused by something they were doing with the supply.
They claimed the RCD was faulty and should be replaced, even though
it was brand new (the house was completely rewired in a reno).
I insisted that the RCD has no clock in it, therefore could not
know when it was 7:58AM, and could not be at fault.

This went several rounds, before they finally admitted that at
7:58 each morning, they switch some large capacitor banks in to
change the load phase, in anticipation of industry firing up some
large inductive loads. They agreed to send sparkies round to
change the RCD to one that's less sensitive to the disruption.

The sparkies reckoned they had done hundreds, to fix the same
behaviour.

There was no fuss about this in the media, and I'm sure that for
every RCD the power company replaced, there were twenty more
customers who paid the bill themselves. Shonky, or what?

Clifford Heath.

Re: Residual current measurement
On Fri, 08 Oct 2010 07:27:05 +1000, Clifford Heath

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The amplifier in most RCD's is sensitive to HF/RF which may be induced
into the core via the line.  We have had many experiences with RCD's
tripping when RF has been superimposed on the line.  Invariably
fitting a common mode choke (ferrite toroid) over the line has
addressed this without compromising proper tripping operation.

Whether the same sensitivity to the supply authority's control tones
exisits I can't say, but it *is* a distinct possibility.  If they have
a 30mA unit replaced with another 30mA unit and it fixes the problem,
you can bet that the replacement has increased immunity to the control
tones aka some additional line-side filtering.

Re: Residual current measurement
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That would certainly match with what both the supplier and the sparkies
told me, given their somewhat low level of technical understanding.

Nice (for others) to know that a toroid could fix it, but for me, even
nicer that someone else did it for nothing ;-).

Clifford Heath.

Re: Residual current measurement

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Cheap electric jug?
That is what does it for us. the element corrodes  and it starts throwing
the RCD. Replace the jug and problem solved.

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