On Tue, 20 Oct 2009 15:46:58 +0100, John wrote:
I m confused as to what switches the heaters on - there are 3 heater outlet
points.

Here[1] they send a signal down the line from the power station (200Hz I
think the engineer once said) to control a set of honking great relays and
switch individual circuits (we've got the dryer on one circuit, the hot
water heater on another, and the electric baseboards on a third; there's
an option for electric underfloor heating too, but we don't have that).

Things go on and off according to power station load (the station shuts
things off at peak demand periods so they don't have to buy in from
adjacent stations) - for the heaters, the thermostats are there to control
how much they're on when they're receiving power. The metering's all done
by a separate meter, slaved off the primary one (so the primary shows
total use, the slave shows cheap-rate use, and they figure out charges
accordingly)

Sounds like your daughter might have a similar setup...

[1] here being the US, but the situation sounds very similar.

cheers

Jules