On 24/10/2013 08:45, Bill wrote:
In message , John
Rumm writes


Hi John and others for your comments, all appreciated.



Your experience adequately illustrates why the "whole house" RCD
arrangement is deprecated - it was never a great idea, and the march
of time (and things with leaky input filters) has only made the
limitations more apparent.

Indeed, filtering is all well and good, but causes lots of other issues.




So is it a practical idea?

Practical - yes certainly. Its the "Rolls Royce" solution that gives
the best possible discrimination in the even of an earth fault.
Obviously its more expensive than other options.


Although cost is, obviously, a factor I feel it would be worth it to
only lose one circuit in the event of a fault. I can only see things
getting worse with more electronics making their way into homes and so
more filtering, unless of course they are manufactured in a well known
far East country where the various components are very obviously missing
from the PSUs by the empty holes in the PCBs, Maybe that is an
advantage of some of these dodgy imports??? There is no leakage from
the filtering because they omitted it to save 5p per unit. But that
is another discussion for another day...



Split load does not have to mean a 50/50 split. Some 17th edition CUs
may have say 4 RCDs and some unprotected (aka "high integrity") ways
as well (for feeding circuits that meet the requirements for not being
RCD protected). You can also arrange the split in various combinations
of ways as suits your application.

Yes, sorry, badly phrased on my part there. I should have just said split.



Yes I am competent to do it, just nervous that I may have missed a
fundamental flaw in the idea.

If it matters the CU is a Crabtree Starbreaker with a single 80A
switch/30mA RCD and 14 MCBs and a DIN mount bell transformer.

Without checking I don't know if you can get single module wide RCBOs
for this enclosure (and if so if there is really enough space to wire
them). You may find you need to replace the enclosure as well.

If no one puts me off the ideas I'm having then checking physical sizes
is next on the agenda. Hopefully in the same enclosure, I'm not too
worried about doing that. But if it came to a new enclosure then the
panic will set in! Although there is plenty of space behind the CU, I
would not look forward too much to replacing it.

Something to keep in mind is that its more difficult to wire a box full
of RCBOs unless the wiring is very tidy. So you may well be faced with
needing to pretty much "start again" anyway to have a hope of getting it
all neatly dressed in the box. Hence the effort difference between
keeping the box and installing a new one may be less than you expect.

No, although you probably ought to look at some pragmatic options. You
may find a combination of several RCDs covering a two or three
circuits each, plus a smaller number of RCBOs would make for a system
that is equally effective, but also leave more money to spend on
improving other aspects of the system.

To get a quick, ball park, idea of cost I checked on TLC's web site
earlier and although scary I managed to not quite fall off my chair. So
if it does come to it I'm hopeful to find a slightly cheaper route.

You could probably find a solution that just uses three or four RCBOs,
and then two or three normal RCDs that in practice will work just as
well. Just identify which circuits are likely to be high leakage (lots
of IT kit, mineral insulated heating elements, water in proximity etc),
stuff that is liable to genuine earth fault (circuits outside, socket
circuits), and then "other" which is low leakage and risk - lighting,
smoke alarms etc.

I'm quite happy with the rest of the electrics in the house, all bar one
slight anomaly which I can easily sort out, just waiting on a round tuit
appearing.

TLC might have em ;-)

--
Cheers,

John.

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