In article ,
PeterC writes:
On Fri, 23 Jan 2009 00:48:42 -0800 (PST), Distorted Vision wrote:

Can someone please tell me what the difference is between RCS mains
sockets with active control circuits and those which are passive?

Active needs mains power to stay untripped, so it will trip
on loss of mains. That's useful if you don't want appliances
to start up after a mains failure (such as garden machinary),
but would be a disaster for anything that should be running
continuously such as fridge/freezer/central-heating/fish-tank...

I was looking at this MK one for our garage:

http://www.mkelectric.co.uk/products...0&rangeid=1030

It has a 30mA rated tripping current. There is also a 10mA version. I
am right in guessing that the 10mA one is better because it is more
sensitive to any residual current?

Many thanks for your help.

For outdoor use (and indeed in most domestic circumstances) 10mA will be a
nuisance; it's used in hospitals for obvious reasons.
My 30mA on the main board trips at 25mA but not at 20mA and hasn't suffered
from over-sensitivity, but 10mA in the garden probably would.

10mA is fine for a single (or very few) appliances, which is what
you're likely to have running from a single socket.
10mA would be a pain in the arse for a circuit which is running
many appliances, such as a standard ring circuit.

My outdoor socket circuit is run from a 10mA RCBO in the consumer
unit, and has never false tripped. It has however tripped very
nicely as I sliced through the hedge cutter cable, without me
feeling a thing. (When a neighbour waves to you, don't wave back
with a running hedge cutter ;-)

10mA is traditionally required for restricted conductive locations,
such as if you are working inside a large metal pipe where you
can't easily move or jump out of way, or let go of the metalwork
you're laying on. It's also useful for poor grounding situations,
such as working outdoors where an earth leakage through you might
be limited to a small current due to resistance of dryish ground,
damp footwear, leakage through tree branches, etc, which might mean
you are taking a sustained 20mA which isn't tripping your particular
30mA RCD/RCBO.

One other comment I'd make is to avoid installing RCD's outdoors or
in damp/condensating places like garages. You do want RCD protection
there, but have the RCD indoors remote from the power outlet, where
it isn't going to suffer from any condensation issues which eventually
kills them.

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]