Simon wrote:

Thanks. Quite a useful thing to have then. Why don't they build one into the
electricity meter and then all homes would automatically have one? An even

On a modern install they almost do. The RCD will usually be present in
the consumer unit where it protects *some* of the circuits (typically
socket circuits where there is a good chance that the socket may be used
to power and appliance used outside, or where there is another
particular risk factor)

People used to install RCDs such that they protected the whole house
(i.e. in the meter tails that fed the CU). The danger here is that you a
swapping one hazard for another. You reduce the risk of death by
electrocution, but *increase* the risk of death by trip or fall. (e.g.
you are drilling into the wall at the top of the stairs on a ladder -
hit a cable in the wall, and trip the whole house RCD which plunges you
into darkness!).

(Note that installs with what is known as TT earthing (commonly found
with overhead power wires) are usually covered by different requirements)

Since many many more deaths occur each year as a result of trips and
falls than by electrocution, the regs were changed to require better
discrimination between faults. Such that completely unrelated circuits
(i.e. lights etc) should not be de-energised when a fault causes a trip
on another circuit

better design would be to have a small light on the meter that came on when
the RCD trips, then you would be able to see to turn it back on again.

This is worth doing anyway. What you require is an "emergency light"
(cost about 20 to 30 pounds). These react to loss of power by turning on
the lamp powered from internal batteries. I added one to my meter
cupboard powered from the downstairs lighting circuit. That way if that
MCB trips the light comes on.

Something like:

http://www.tlc-direct.co.uk/Products/EMWP3NM.html

or if you want to use it as an ordinary light controlled from a switch
as well then:

http://www.tlc-direct.co.uk/Products/EMWP3M.html

See also:

http://www.tlc-direct.co.uk/Technica...ting_Guide.pdf


--
Cheers,

John.

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