On 22/06/2015 11:37, wrote:
On Monday, 22 June 2015 11:05:10 UTC+1, John Rumm wrote:
On 22/06/2015 09:56, Jim x321x wrote:
John Rumm wrote in
:

with the existing setup, and I rarely get any inexplicable
tripping of the circuit breakers. As far as I am aware, the
old fuse boxes (even when fuses contained fuse wire) did
what they were designed to do, with no problems.

They did what they were supposed to - and will still do so.
The main thing your current setup lacks is RCD protection.


Thanks to all for the excellently helpful advice.

If I added an RCD covering the entire house (without replacing
the existing fuse box which is already fitted with MCBs, would
that constitute a change to the wiring and thus require building
control notification?

Firstly you don't want a single RCD covering the whole house -
that is a practice that was common during the 15th edition, but is
deprecated now since it offers no "discrimination" in the event of
a fault (i.e. the fault will take out the supply to the whole
house, not just the circuit causing the problem). So many circuits
on one RCD are also more prone to nuisance tripping in the first
place.

A single RCD is moderately likely to not even work.

True, but the failure rate is not high enough to make that relevant I
would say. (IIRC, 15% of those that have never been tested may fail to
operate when they should - but that sill leaves 75% that will work and
potentially prevent an injury)

Would doing this significantly improve the house's safety rating
in the eyes of, say, a house-purchaser's surveyor?

Only if the purchaser is sufficiently clued up. You may find an
older CU etc would be commented on during a survey, but only in as
much as the surveyor might comment that you could get an
electrical report if concerned.

Surveys say get it checked regardless. A buyer that understands RCDs
- few do - is one that can do the job themselves if they want.

Indeed. Hence my comment about it not being something that will help
"sell" a house.

So if your only reason for the change is to make the house more
saleable, I would not bother. If however you are planning to carry
on living there, then its worth it (IMHO) for other reasons.

Work out the cost & size of risk reduction. Compare with other
options. The benefit per pound is far from top of the list.

If your only criterion is avoidance of death due to electrocution, then
the argument is plausible, since from a statistical point of view you
may as well ignore the risk of death - its low enough to be insignificant.

None of that however diminishes the effectiveness of a RCD at preventing
shock injury - the occurrences of which are commonplace rather than
rare. (100's K of hospital admissions per year)


--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/