Measuring power

Chris Benson chrisb at
Thu Apr 30 10:10:30 BST 2009

On Wed, Apr 29, 2009 at 12:05:21PM +0100, dhs at wrote:
> On Apr 29 2009, Chris Benson wrote:
> Indeed: one of those "simplifications" they make in teaching O-level  
> (sorry, GCSE) physics (that dates me... :-)

But I don't remember it coming up in A-level physics either, (but I was
well on the way to dropping out by then so may have missed it!).

>> Of course VA maybe what you want.
> Probably: that's what the power company bills you for...

Domestic charges are per the meter: kW.  

But at work, due to a screw-up in the power layout of our spiffy new
machine room, we were being charged for 120kVA across three phases though
we were only using 48kW (as recorded by the UPS) -- but mostly from one
phase.  Apart from the cost we were causing (earth-leakage?) problems at
the substation: We had to do a full shutdown and scramble round under
the floor to try to spread the phases out better, while ensuring we
didn't mix phases in racks.  Joy!

I'd like better power meters for both domestic and work: the Sun racks at 
work have power control units -- but no power consumption monitoring, and
the domestic meters are too large to fit on every device :-(
Chris Benson

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