For many, possibly most, electrical applications (e.g. electric water heater,
any heating appliance, most motors) the "on" amps are always the same so you
only need to measure that once with your favourite clamp AC ammeter:
http://img.directindustry.com/images_di/photo-g/ac-dc-ammeter-clamp-16624-2558571.jpg
... and then multiply by the number of minutes the device is "On".
Notice that the clamp ammeter, above, does not attach electrically to the
circuit so it is totally safe for any level of power and voltage. Here's an
article on building a very simple on/off sensor for appliances:
http://cocoontech.com/forums/topic/6864-how-to-sense-power-onoff-toggle-via-one-wire/
Now some things use (or produce!) variable AC amps so you do need to measure
these. Typically for these you use an inexpensive "split core transformer"
(google for images) then rectify it, and measure the voltage using your
favourite 1-Wire A/D sensor.
Again this solution does not involve an electrical connection to the AC circuit.
--
Daniel MacKay
Senior Monitoring Designer
SHINES Renewable Energy
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