On Wed, 3 Aug 2005 20:39:54 +0100, Will James wrote:

The conclusion of the experiment is, that if a submerged 'break' in the
insulation of the live etc occurs some distance away from a good earth a
30mA RCD may not 'see' enough leakage current to trip and thus the water
will still be live. BTW my 30 mA RCD was and is working perfectly well,
in fact I measured the current required to trip it and that current
was, from memory, in the low to mid 20 mA range, ie below 30mA.
An american, Johns, repeated the experiment with a US spec 5mA tripping
RCD/GFI and that did trip, see the 2nd of the links above. I would
therefore suggest that you try to get a 5mA trip RCD, unfortunately I
dont know if they are available.


--
sean mckinney
Thanks for everyones replies. I am in the UK, if I understood Sean correctly
I think you are saying if I cannot get hold of a 5mA RCD, it would be better
to have an RCD with an earth as near as possible in cable length terms to
the pond as well as an RCD inside which would trip the circuit if a spade
went through the outdoor cable?

I think what he is saying is that with a break under water the leakage
to earth was less than 30mA due to the high resistance to earth. Maybe
the pond was lined with butyl or some other insulating material. The
water would rise to 240volts but it wouldn't harm anything and if you
put your hand in the trip would fire before enough went through you to
do any harm.

You can get all sorts of trips and I'm sure B&Q will do a selection.
Most trip at 30mA but you can get them as spurs or single/dual sockets.
I don't know what the relevant BS standards that are quoted mean but
they may not necessarily be a standard for tripping. For instance all
BS1363 means is that the plug insulation will withstand 10,000 volts.

--
Regards - Rodney Pont
The from address exists but is mostly dumped,
please send any emails to the address below
e-mail ngpsm4 (at) infohitsystems (dot) ltd (dot) uk

Will James Wrote:
Thanks for everyones replies. I am in the UK, if I understood Sean
correctly
I think you are saying if I cannot get hold of a 5mA RCD, it would be
better
to have an RCD with an earth as near as possible in cable length terms
to
the pond as well as an RCD inside which would trip the circuit if a
spade
went through the outdoor cable?

Thanks,

Will

[/i][/color]
Sorry but no, what I am saying is that in my opinion a 30mA RCD cant be
relied upon to make a pond safe. The problem is that the water is
resistive and as such as the distance between the source of the leakage
and whatever provides the electrical earth in the pond increases the
leakage current quickly drops below the trip value for a 30mA RCD,
salted water is probably more conductive than unsalted water so this
may not be a concern in a salted pond but I dont salt my pond.
In practical terms I assume that most UK pond devices, pumps, lights
etc, are earthed, I have yet to see an unearhed UK device, and that the
earth point is very close to any likely source of leakage, UNLESS a
cable gets nicked, so a 30mA RCD would most likely trip. However should
the fault be a cable nick etc the RCD may not trip. IMO the length of
the earth wire is irrelevant providing all connections are good.


--
sean mckinney