Date   : Thu, 17 Sep 2009 11:04:59 +0100
From   : philb@... (Phil Blundell)
Subject: Leccy @ Acorn World '09

On Thu, 2009-09-17 at 10:19 +0100, Mick Champion wrote:
> So that means the USA only gets half the available power we do then?

On typical 120V outlets, yes: even leaving aside the question of the
circuit rating, the standard NEMA 5-15 socket outlet itself is only good
for 15A. 

However... the tradition in the USA is to supply residential buildings
with split-phase power (i.e. a three-wire 120-0-120 feed, derived from a
centre-tapped transformer).  The common NEMA-1 or NEMA-5 sockets supply
one phase plus neutral, but larger appliances use a 4-pin socket known
as NEMA-14 which provides both live feeds as well as neutral, giving you
240V between phases at a current rating of up to 50A.  

It's not such a bad system: the highest potential to ground at any point
is 120V, and in most of the inhabited parts of a building the highest
potential between any two accessible points would be 120V as well.  (The
NEMA-14 outlets tend to be fitted in utility rooms and those kinds of
places.)  So, compared to the European 230V system I guess they enjoy a
slightly reduced shock risk.

You're right though that it wouldn't be practical to roll up with a Baby
Belling or a 3kW heater and expect to be able to plug it into an outlet
in the living room.  

p.