In message ,
"Christian McArdle" wrote:

At 5x current most seem to manage around 10ms. Again though, I realise
that this is a feature of the RCD, not a specific requirement of the BS
disconnection times.

It's probably quite difficult to design an RCD that doesn't instantaneously
trip at the next crossing point (or the next crossing point of a particular
polarity). It would need some sort of additional time delay mechanism, like
those intended for TT system incomers.


I see what you mean - that if there is sufficient current flowing (about
1x the operating current) the thing should trip. Does it trip at the
crossing point (when the current is effectively zero), or at the peak
voltage, hence peak current? The tests I carry out (and which usually
involve a lot of running up and down ladders) are quite interesting:

1: at half rated current the device should not trip, tested at 0
degrees, 180 degrees and then 0 degrees again.

2: at rated current it should trip within a specified time, test and
discard reading at 0 degrees and then take reading at 180 degrees and 0
degrees again.

3: at 5x rated current it should trip within the specified time (e.g.
40mS), three tests as in 2:

That's usually nine tests in all, and the nearest convenient socket at
which to plug the tester in is rarely within arm's reach of the RCD :-)

Hwyl!

M.

--
Martin Angove: http://www.tridwr.demon.co.uk/
Two free issues: http://www.livtech.co.uk/ Living With Technology
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