Sorry, "American Electrics" was getting far too OT, and rather long so
here it is:

Given the opportunity (and let's ignore backwards compatibility, at
least to begin with), how would you redesign our domestic final circuits
to be completely idiot proof?

Although the system we have at present is probably the most recently
designed in the world, are there any things about it which, with today's
technology, could be seen as compromises?

Particular examples brought up on the AE thread (and elsewhere over the
last few months):

* a ring circuit with a break in one of the live conductors will
overload one leg as it is fused at 30/32A and the cable is only good
for 20A (27A under ideal circumstances)

* fuses in the appliance plugs can be bypassed, while MCBs screwed into
the consumer unit are less likely to be.

* fused appliance plugs are better for isolating faults to a single
appliance as (usually) the plug fuse will blow before the MCB.

* on the other hand, in a "dead short" situation, this isn't always the
case even with a 3A fuse and 32A MCB (I've proved it several times
:-)

* radials using fused plugs can be rated up to 32A, but need at least
4mm2 cable, and often 6mm2 cable which is both more expensive, and
much more difficult to work with than the 2.5mm2 cable used for 32A
rings.

* unfused appliance plugs (less problem with tampering) would mandate
radials with a very low MCB rating and hence a large number of
radials; one per room or even more.

* either that, or they would mandate fuse protection inside every
appliance and while a lot (TV, video etc) already have this, it's
going to be difficult persuading manufacturers to bung a fuse inside
a £3 table lamp.

* unfused appliance plugs will *always* take out the circuit MCB on a
fault, and hence tracing the appliance which caused the fault can be
tricky since there are likely to be several candidates.

Erm, I'm sure I've missed some things out.

Go on then, what's the ideal? Sub mains to each room with a mini-CU in
every room, with MCBs feeding individual outlets (don't laugh, it has
been suggested)? Appliance plugs with built-in MCBs rather than
replaceable cartridge fuses? Sockets with built-in MCBs, or RCBOs?
Talking of RCDs, what about changing the way we use these things?

Have fun :-)

Hwyl!

M.

--
Martin Angove: http://www.tridwr.demon.co.uk/
Two free issues: http://www.livtech.co.uk/ Living With Technology
.... Beware of quantum ducks. Quark! Quark!