On 2 Sep, 20:48, "Jerry" wrote:
"John Rumm" wrote in message

...
: On 02/09/2010 10:33, Jerry wrote:
:
: Only if you are being a pedantic fool and taking the meaning
of
: the word "House" to me a multi floor dwelling rather than the
: more usual generic meaning of the word as a place were people
: live. Anyway, even if there was multiple ring circuits one
faulty
: device will still take out all devices being powered from
that
: circuit rather than just the one or two that would be on a
radial
: circuit.
:
: Although I suspect that Jerry has not realised it, his beef
seems to be
: with fused plugs, since he has actually highlighted nothing of
relevance
: to circuit topology.

Yes, and I have said that both radial and ring circuits have both
advantages and disadvantages.

*Plug fuses can be abused (as can rewireable fuses
: in consumer units), however in reality this much less of a
problem that
: might be imagined.

But we are talking about (theoretical) risks, allowing the
ignorant to defeat final protection with not much more than a
kitchen or pen knife and thus compete for a "Darwin Award" has a
very much higher risk factor than many of the risk that the regs
are obsessed with now!

Most appliances are designed to be sold all over the
: world, and hence will usually have a flex that is capable of
surviving
: faults with only 16A head end protection (as would be common in
some
: countries),

Not so sure, whilst many appliances are sold all over the world,
since the UK law has required the pre-fitment of BS1363 plugs
complete with the correctly rated BS fuse many appliances now
come with power leads not only with moulded on plugs but the lead
rated to the fitted fuse IYSWIM.

*hence the fact that someone might substitute a 13A fuse in
: place of a 3A is not likely to be a problem with most
appliances. There
: is the remaining issue that one could substitute a solid object
for a
: fuse, but that does not appear to be something that happens
regularly.
: Quite possibly because it is very rare for plug fuses to blow
in the
: first place.

How do know the practice is rare or not, only when something goes
dramatically wrong will the miss-use ever become apparent and if
protecting an appliance with a grossly over-rated device (15A or
even 30A instead of 3A) isn't really that much of a problem then
the rational behind the original design of the BS1364 plug/socket
must be in question! Also any appliance that does need careful
protection should perhaps have to have a 'tools-only' accessible
internal fuse anyway?

:
: The absence of a plug fuse requires that the protective device
at the
: head end of the circuit can clear not only overloads of the
whole
: circuit, but also faults that may occur in light weight
appliance
: flexes.

But that IS the way things are going anyway, hence stories of
RCBs tripping out because someone has pluged in a doggy table
lamp in one room and taking out the supply to someone using a
computer in another and thus their unbacked up work - and don't
suggest that they should have had the computer on a differant
ring circuit, "Average Joe" and his family use what the
builders/electritains have installed.

This second requirement places significant restraints on the
: circuit as a whole, and drastically limits the total power
supply
: capability. Hence the proliferation of inflexible[1] low
current rated
: circuits you get in places like the US.
:
: [1] Think about a kitchen / utility room with tumble drier,
dish washer,
: and washing machine. That could represent 8kW of load -
although it
: would be diverse - the chances of all three being in use at one
time is
: relatively small, and the presence of thermostatic controls on
the
: heaters will mitigate further. These could safely be power on
one 32A
: ring circuit, but would probably require three 16A or 20A
radials to do
: the same job.
:

Indeed, or perhaps even a sub-main feeding a sub-board. Also,
remember if these appliances/utility room is feed via it's own
ring circuit this requires two of the two out of the three cable
runs needed for the radials anyway, cost savings will be minimal
and thus I would prefer the redundancy given by radial circuits,
also radial circuits and 15amp unfused plugs would remove the
issue of either BS1363 plugs stuck behind these difficult to move
appliances, plug and sockets being fitted in cupboards, trailing
leads or hard-wired flex outlet plates.

Most owners don't care how many, or indeed the cross section of
such, wires have been installed in a building (even the fitment
of 5amp lighting points in the wall), what they do notice is
price (of new house or re-wiring a old house), so the choice of
ring vs. radial circuit comes down to cost at the end of the day,
not really the technical pros and cons of each.
--
Regards, Jerry.

Have you ever been here?