Measuring power

Chris Benson chrisb at
Wed Apr 29 10:53:30 BST 2009

On Wed, Apr 29, 2009 at 10:05:01AM +0100, Michael Lush wrote:
> A frend of mine has a Power Owl
> You clip the sensor round the mains power were it comes in to the  
> electricity meter.  I guess you could clip it round the server power 
> cable
> I'd be inclined to calibrate it against a inline power meter before use...

I have a similar meter from Efergy at home and once spent a frustrating
weekend trying to get it to agree with the official meter.

Eventually I realised that these meters are measuring VA, not W.  The same
for resistive loads, but considerably different for inductive loads such
as CFL and electric motors.   I have one "32W" CFL that draws 67VA.

Of course VA maybe what you want.

I got a few inline power meters from Maplins when they were on
offer at 9.99
(But they're now 22.99!)  Ah, the current "deal" is  @ 7.99.  OK for
domestic use but that doesn't really help in a rack or if you can't
unplug the server.

There must be a market for better power monitoring: I'd like a meter
that piggy-backs in the circuit-breaker socket of a distribution board so
that I can monitor each circuit.  Individual devices would be even better!
Chris Benson

More information about the mailing list