In message ,
"dennis@home" wrote:

[diversity/ring circuits]
I understand them..
I just don't agree with them.



Without diversity modern living would be impossible. In the
one-radial-per-room scenario we would have at least eight radials in
this small house. Even if they were all 16A that's a non-diversified
8*16A you have to cater for which is 128A which is well over the
capacity of even the largest normally available service fuse (100A).
Without diversity you'd have to assess a cooker at its maximum rating in
the same way as a shower. One 8kW cooker and one 8kW shower makes 66A
while many houses are still on 60A service fuses.

Now I know that this isn't really your argument. You are arguing that a
ring circuit is unsafe because in the event of a break it is 2.5mm2
cable fused at 30/32A and the cable is only rated for 27A at best. I
don't know the figures, but Peter Parry has over the years proved to
have done rigorous research (look for his postings when Part P was
originally proposed) and I am much more prepared to believe him when he
says that the UK system (and by implication the ring final) is amongst
the safest in Europe than I am to believe you who states with no
backround evidence that a many-radials method would be safer.

Its just another compromise to save a few quid (very few these days)


It has probably never saved very much money. The tortures of installing
a ring in certain shapes of houses makes you wonder why people didn't
use radials more often. In the terraces around here they often did.
Where can you buy 20A fuse wire these days? Actually, on that subject,
that's an area where a 3036-protected ring may actually be safer than a
radial: fuse wire of 20A is not commonly available any more, so if a 20A
fuse blows it may be replaced with 30A wire. Wire greater than 30A is
likewise not commonly available so a blown 30A ring fuse is only likely
to be replaced with 30A wire. (Let's ignore the cases where fusewire
isn't used at all and blown fuses are replaced with bits of copper
stripped from T&E)

To be at serious risk of damaging a correctly functioning ring you have
to have a series of improbable coincidences. Either that or the central
heating has broken down, it's the middle of the winter, and you've
managed to find the one homeowner in the town who has more than three or
four portable electric heaters.

Sure, a ring final *is* a compromise (of sorts), but it is a
well-engineered, well-calculated, conservatively-rated and provably safe
compromise.

Hwyl!

M.

--
Martin Angove: http://www.tridwr.demon.co.uk/
Two free issues: http://www.livtech.co.uk/ Living With Technology
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