power meters

[Ric Werme]

> PS: For 220, you can measure the two live legs using 2 separate meters.
> But in general, things like dryers and ranges will have the same
> readings for both legs.

>From what I remember of my stove wiring, the heating elements went
directly between the + & - 120V legs, and may not have had any connection
with the common.  The clock and lights just use one leg.

A device like the Kill-A-Watt wouldn't be very pleased, no matter how
it's hooked up since it's only rated to 15 Amps or so.

> BTW: You're dealing with deadly power here. I don't recommend cobbling
> this together unless you know what you're doing.

I only got zapped by 220 once.  Actually, 120 may be worse as that can
induce fibrillation if your heart is part of the circuit.  220 is more
of a hard reset (heart reset?).  I don't recommend either.  :-)

The thing that makes monitoring such big appliances interesting is that
even if you know the power draw, you tend to not know the duty cycle.
Unitil replaced my power meter with something they can read over the
power lines.  I've never gotten around to asking them if I could read
that on demand (e.g. from a crontab entry).

     -Ric Werme