Adam,

On Sun, 14 Sep 2003 13:14:57 -0400, M. Adam Davis wrote:

> Howard Winter wrote:
>
> >This had never occurred to me before - the American
> >wiring scheme, where the only fuses/breakers are at the
> >distribution box, means that there's nothing to stop you
> >adding dozens of multi-way socket-strips to each other,
> >and plugging into a single wall socket.  So nothing
> >technical stops an overload until you exceed the whole
> >circuit's rating - have I go this right?
> >
> >
> The breaker at the fuse box is rated for the largest guage wire in the
> given circuit.  For instance, if you put in a 20 amp breaker, you must
> use 12 guage wire for the entire circuit.  The outlets are typically
> only 15amp, so it's possible to pull 20amp through an outlet rated only
> for 15, but it is not a major hazard.

I understand the installed-wiring part (which is obviously subject to regulations) but what about multi-way
extensions?  Do they always have 20A-rated cable?  This is the only way I can see that it would be inherently
safe (protected by the circuit fuse/breaker) as opposed to relying on the user not to overload it.

> It's recomended to put in 15 amp breaker with 14 guage wire with 15 amp
> outlets.  Thus you can pull all 15 amps from one outlet without worrying
> about the wire's heating too much.

So that means you have a maximum of about 1.65kW on any device, doesn't it?  And while doing so you can't use
any other socket on that circuit.  Isn't this a bit limiting?

> When I re-wired my basement for my electronics workshop I put 12 guage
> everywhere, with 15 amp outlets and a 20 amp breaker.  I knew that I
> wasn't going to be pulling more than a few amps from each outlet at
> most, but since I was only running one circuit per room (seperate
> circuit for lights) and I might be pulling more than 15 amps total in
> the room it made sense.  The inspector had no problem with it.

There's obviously a very different strategy to wiring there compared with here.  My house has two "power"
circuits for sockets (upstairs and down) at 32A, one "lighting" circuit (6A), plus a single radial for the
immersion heater (20A).  That's a bit stingy on the lighting, but it's a small house, otherwise that's pretty
much how houses are wired here.  The "power" circuits are rings, where a 2.5mm (cross-sectional area of the
conductors) cable runs to each socket in turn and then returns to the distribution board, so any current is
divided and passes "both ways" round the ring.  That's how it's been done here since the 60's (at least).

> The seperate light circuit was for when I blew a breaker - I wouldn't
> have to do any further troubleshooting in the dark.  Fortunately since
> then I've never had an issue with the power.

Lighting is always on a seperate circuit from power here, and uses much thinner cable (1 or 1.5mm) and a much
lower fuse/breaker rating (6A, usually).  I don't know what your cable gauges are, but 1mm is rated for 14A,
1.5mm is 18A and 2.5mm is 26A.  There's also 4mm and 6mm for special purposes, but I can't remember their
ratings.

> >(As a matter of interest, in Britain we have fuses in
> >each plug, with a maximum of 13A - approximately 3kW -
> >so you can't exceed this via any single socket because
> >extension leads/multiway strips have a fuse in their
> >plug too).
> >
> Most 6 outlet extensions have a breaker built in.  The rest all have
> fusible links. ;-) Just don't place the wire near anything flammable! =:-o

That doesn't sound very confidence-building!  On my next trip to the US I think I'll bring a smoke detector
:-)

Cheers,

Howard Winter
St.Albans, England

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