On Fri, 25 Jul 2014 06:53:39 -0700, Baron wrote:

aeio prodded the keyboard

On 24/07/14 22:08, Baron wrote:
aeio prodded the keyboard

...just started snipping....
A reading that small could just as well be leakage. Are you sure
that should be milliampere and not amps ? ie 5 ma.

Yes - 0.005 mA. That is on the 2mA scale. There is nothing showing
on the higher scales and nothing on the AC scale.

In that case I would be inclined to forget about it. But just in case
check it regularly to make sure it isn't getting worse.


Inside every computer is a line filter to prevent the switching power
supply signals from going back out your AC mains, called conducted EMI.
Inside that filter is a cap between NEUTRAL, HOT, and chassis GND, called
a Y-Cap. That y-cap effectively centertaps your AC mains, but usually the
PC case is connected to earth ground, almost equal to NEUTRAL, so you
never measure any voltage there. If the GND terminal on the outlet to the
PC is floating, well you can get a pretty healthy zap. I can just start to
feel 12Vac so this 60-70Vac hurts a LOT! The size of the y-cap is set to
just about provide a maximum of 2mA.

Now such filtering on an isolated DC supply [if the whole thing is DC
isolated from the PC chassis] can also cause the metal housing's voltage
to meander around.

For what it's worth, 'hospital grade' leakage is less than 100uA and
'direct onnection to patient' hospital grade leakage is less than 10uA
....to simulate what that feels like the next time you're in a store with
fluorescent lighting inside a metal trimmed display cabinet. Gently slide
the back of your knuckles along the metal. You probably will feel the AC
mains voltage. Now, *if* you touch an open wound to that metal! That's a
big oweey, hurts like h---.

The only concern I would have about finding strange voltages where not
expected is that that may be a precursor to a failure mode that would then
supply BIG voltage, as in lethal voltage, if/when something else happens.