On 21 Aug, 14:33, David Hansen
wrote:
On Tue, 21 Aug 2007 13:55:12 +0100 someone who may be "Tim Downie"
wrote this:-

A friend of mine has a pond with pump & lights wired into a fused spur from
the house ring-main (which is RCD protected). After some recent heavy rain
(which probably managed to penetrate a supposedly "water-tight" outside
junction-box, the RCD tripped, which wouldn't have been a problem if he
hadn't been away on holiday at the time and the fact that the freezer was on
same circuit. [snip]
Would I be right in thinking that this wouldn't necessarily stop the main
fusebox RCD tripping?

Yes.

Would one with a lower (20mA say) trip current work (and do such things
exist)?

It would work in that it would disconnect the supply. However, it is
likely that the main one would also work.

In this sort of situation you need a time delayed one on the main
board, but this gives rise to other difficulties.

....such as the fact that they are scarily expensive. Cheapest I found
was from CPC a couple of years back. £85 + VAT IIRC.

Jon.