In article ,
Peter Parry writes:
On Tue, 11 Nov 2008 21:17:23 +0000, Hugh Jampton
wrote:

I changed my dual fuel tariff with EON recently. New one is fixed until
next October. With my new deal came a "Energy saving monitor" - it tells me
how much electricity I'm using.

I've checked the readings of the monitor against my meter readings. The
monitor tells me I'm using approx. 15% less than my meter readings.

Are these monitors that inaccurate ? Or could my meter be over reading my
usage ?

The "whole house" monitors which clip over one of the feeds to the
electricity meter and have a remote reader are really quite
inaccurate, vastly more so than the meter. They are mainly greenwash
where being seen to be doing something is considerably more important
than actually achieving something.

They can't measure power at all -- the reading is a guess.
They can only measure current, and then have to guess the
voltage and phase angle to estimate the power.

The ones you plug into a socket and then plug the device into them are
quite accurate even when the load is "difficult" (such as switched
mode power supplies).

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]