Huge wrote:
On 2008-07-24, John Rumm wrote:
Richard wrote:

Hmm. My place has an 80mA RCD protecting the 13A sockets. It's a
standalone RCD feeding the CU which contains only a double pole 100A
isolator. Is that (still) acceptible?
It is probably a 30mA trip RCD with 80A switching capacity. If that is
the only CU, then no it is not an acceptable solution these days, since
one fault loses you all power and lights.

In the 15 years we've lived here, our similar arrangement has only ever lost us
"all power and lights" when some idiot (me) drilled through a ringmain. OTOH,
the power compnay plunges us into darkness several times a year. Sometimes
several times a day. So I'm not going to lay awake nights worrying about it, and
I suggest the OP does likewise.

There are two issues here really. One is the nuisance factor in day to
day life, and the other is the genuine fault scenario.

Peoples perception of problems with the single RCD setup seem to be
governed by the former, while it is the latter that in many cases has
more potential to bite you.

Some single RCD setups (like yours, or the setup at my mum's previous
place) never trip unexpectedly, and hence can lead you to assume there
is little or no risk. Others, like that which was here when we moved it,
tripped any time a horse farted or so it seemed[1] and was a right royal
pain in the arse. Hence there was a big motivation to fix it for that
reason alone.

(The supply also goes off with some regularity here as well - hence why
I am fitting emergency lights in strategic places. Having navigated my
way back to the CU in total darkness on a few occasions when it was just
a RCD trip, it was apparent that to get the whole family out, possibly
in the presence of smoke, in the same situation would be very difficult)

However the fact that you get no nuisance trips does not mitigate the
problem of being left in an awkward situation in complete darkness when
the RCD does its job protecting you from a real fault. This may be an
exceedingly rare event. How much of a problem this actually is will vary
greatly on circumstances. Someone in a well street lit road, young and
mobile enough to find their way back to the CU with no difficulty is not
really under any risk. Old, infirm, out in the sticks, up a couple of
flights of awkward stairs etc and the picture is very different.

So my advice would in some circumstances concur with yours, but only
after one has assessed their circumstances and thought through what
factors are going to come into play.



[1] Combination of ten circuits including several outdoor ones all
protected on one over sensitive 30mA trip RCD.


--
Cheers,

John.

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