"Andrew Gabriel" wrote in message
...
In article ,
"Sparks" writes:

If I recall correctly, 40mA will kill you, therefore RCD's are set to
trip
at 30mA

So can 30mA, but not normally within the time it takes for
an RCD to trip.

The whole purpose of an RCD is to try to prevent people getting killed
from
electrocution

No, that's _one_ purpose.
Indeed RCD's used for providing protection against electrocution
must not exceed 30mA rating. However, RCD's protecting a whole
installation (due to excessive earth fault loop impedance) must be
at least 100mA, but cannot be used to provide protection against
electrocution. Hence a single RCD cannot do both jobs.

installing a 100mA breaker, IMO is madness

A direct swap is indeed silly. The installation was wrong before,
and is now wrong in a different (possibly more dangerous) way.

The only reason I can see to use a 100mA breaker, would be to feed it's
output directly into several 30mA breakers to keep a handful of circuits
separate
(for example, mains in -100mA breaker, then this feeds to house 30mA
breaker and another 30mA breaker for another building.

No, that doesn't work. RCD's don't discriminate on current.
You should avoid daisy chaining them at all, but if you have to,
the one nearer the supply has to be a time delayed type.

100mA and greater RCD's are for protection again high earth
impedance, where a short to earth might not pass enough current
to trip the fault current protective device within the required
time (or even at all). This is commonly the case where the system
uses an earth rod for earthing.

--
Andrew Gabriel

Hmmm, that's interesting.

One of my projects for Q1 next year (ie before the draconian new regs appear
and drive the cost up to the point where I won't bother) is to replace my cu
rrent CU.

I've read through a number of posts on the matter, and will be getting hold
of a 16th edition on-site guide soon, but initial plan was to install an
isolator before the CU, and replace the current one with one populated with
a mixture of RCBOs and MCBs, possibly splitting my office off onto it's own
ring, protected by an MCB due to the amount of computer equipment in there.

I had been uncertain as to whether the CU should have overall protection of
a time-delayed 100mA RCD, but from what you say this is probably not
necessary nor desireable. The earth is supplied by the provider.

Is this about the size of things?

cheers
Richard

--
Richard Sampson

email me at
richard at olifant d-ot co do-t uk