Date   : Sat, 11 Mar 2006 10:25:13 GMT
From   : Pete Turnbull <pete@...>
Subject: Re: Them pesky case stickers (was 1MHZ SCSI/ATA board.)

On Mar 11 2006,  1:54, David Hunt wrote:

> Does the meter take account of the power factor ?

Yes, as I said, it measures true wattage.  Unless the mains waveform
becomes *extremely* distorted by the load -- and it's very hard to make
it that badly distorted.

> Like I said, I didn't measure the current and multiply by the
voltage, I
> just compared two electricity bills over the same period.

Sure, but to calculate the current from the wattage, as I did earlier,
one needs to apply the power factor as a correction.  You can easily
have a setup where the current is close to the limit for a breaker but
 because of phase shifts the power is actually quite low.  Conversely,
in most systems the current is higher than would be suggested by casual
examination of power level, and you often have to do the calculation to
check that things are safe, or that a breaker won't trip.  I wanted to
know if 12kW was a plausible level in terms of the current supplied in
a commercial/domestic environment so I did the calculation.

Just as a matter of interest, what was the temperature in there?  12kW
is an enormous amount of heat.  A sizable chunk of the total used by
our University machine room, which has two massive aircon units to keep
the temperature down to 21C.

-- 
Pete                                           Peter Turnbull
                                               Network Manager
                                               University of York