On 27 May 2005 01:18:10 -0700 "larry moe 'n curly"
wrote:

Backup supply plugged into AC outlet;

hot-neutral: 120 VAC
hot-ground: 120 VAC
neutral-ground: 0.7 VAC

Backup is line powered and is just passing thru the relationship that
your AC line has.

Backup supply unplugged from AC outlet, computer used as load:

hot-neutral: 115 VAC
hot-ground: 58 VAC
neutral-ground: 58 VAC

As someone else said, ground is floating and the load leakages are
pretty nicely balanced, and lower impedance than your Fluke.

Backup supply unplugged form AC outlet, no load:

hot-neutral: 115 VAC
hot-ground: 19 VAC
neutral-ground: 60 VAC

Here the output is completely floating, but you can see that the
leakages in the backup are not particularly balanced. The 10 MOhm
impedance of the Fluke is significant here; it has pulled each one
down a bit so that the last 2 numbers no longer add up to the first.
If you had a second Fluke so that you could actually make those 2
measurements simultaneously, you would get numbers that add up right.

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Jim Adney
Madison, WI 53711 USA
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