"Andrew Gabriel" wrote in message
.. .
This thread has got the ring/radial issue mixed up with
local/central circuit protection. I'm not going to try and
unravel that confusion now as it will just complicate the
thread further, but the two issues are really quite unrelated.
Further comments interleaved...

In article
ws.net,
":::Jerry::::" writes:

"Dave Plowman (News)" wrote in message
...
In article
ews.net,
:::Jerry:::: wrote:
But how many idiots then put the wrong rating of fuse in when
they
try to use a 5amp extension to supply a 3Kw fire.
That could not happen if the protection device was back at the
board
and needed more than a dining table knife blade to open...

What happens instead is, "Oh, I wonder which appliance blew the
fuse?"
Start trying them all in another circuit, and eventually BANG!.

Err, how many appliances are you plugging into a single outlet ?...

"Oh it must be this one". That's the best result in this
circumstance
-- you only blew the circuit protection twice and generated two
small
explosions in some appliance, which is the best you can do with
such
poor circuit/appliance protection.

Err, most people would replace the fuse and try the appliance again
anyway, exactly the same result.....

The not so good result is you try
them all and they all work fine. So now you have a faulty
appliance,
you don't know which, and you're going to carry on using it until
it
fails again, maybe worse next time.

See above......


IMO radial circuits were far safer from abuse, although they
were
more expencive to implement correctly, the ring circuit (as
used in
the UK) is a 'one size fits all' solution that is wide open to
abuse.

Yes, well you don't understand it. But don't worry, that's
quite common.

So protecting something at a 15 A rating is less safe than doing so
at 30 A when someone replaces the fuse in a BS1364 plug with a bolt
or what ever, as has happened ?....


The design starts by looking to see where the failures tend to
be. They tend to be in the appliances and appliance cord, i.e.
the parts which get moved around, and not in the fixed wiring
which is generally well protected from degrading effects. So
to localise such failures, protection is applied at the start
of the common failure path, which is the appliance plug. This
has a big advantage that the protection is intimately associated
with the item it protects, so when you have a faulty appliance,
there is never any question of which appliance it is (ignoring
RCD's, which are a later 'problem'), or of moving the faulty
appliance to a different socket and continuing to use it.

So still have local protection if that really is going to be a
problem.


There is nothing to stop any idiot, who can open a plug, replacing
a
3amp fuse with the shank of a 8mm bolt, with radial circuits and
final protection back at the distribution board that is not so
easy,
especially if that final protection is via circuit breakers - so
yes,
the final 'ring circuit' is wide open to abuse. It was years
before

Strange that the EU countries with radial circuits generally
have twice as many electrical incidents as we do (and that's
ignoring the ones with poor quality wiring).

all appliances came pre-fitted with plugs and the correct fuse,
how

Well, that's because prior to around 1970, it wass illegal to
supply an appliance with a plug in case it was the wrong type,
someone cut it off, and then stuck the resulting loose plug
and exposed flex into a socket. That was just one tiny part of
the problem of having multiple socket types. By 1970 (can't
remember the exact year), judgement was that sockets other than
13A were now sufficiently rare that the law could be changed to
require a BS1363 plug to be fitted to all appliances which were
expected to be plugged in to a socket.

Err, it became law in about 1990 IIRC, and as for sticking wires into
sockets, the non fitment of any plug increased that risk !


many people fitted a plug without then changing the supplied 13amp
fuse to the correct lower rating?...

All new appliances nowadays are required to remain safe with 16A
protection, so actually you can leave a 13A fuse in everything
sold in last 10-20 years.

But not 30A when some idiot uses a bolt to bridge the fuse....

Exceptions are old appliances with
longer thinner flexes (which are no longer allowed), and extension
cords, whose ratings are horribly complicated anyway, but you
aren't going to dangerously overload any extension cord you buy
today at 13A providing you fully unwind and don't cover it (there
are other complications though).

As I said, the final ring circuit is a 'one size fits all'
solution
that is open to abuse.

But seems to be around twice as safe as most of its EU
alternatives, fortunately for us.


More by luck and good education than the safety of the system I
suspect.