Harold,

On Thu, 5 Jan 2006 10:00:18 -0800 (PST), Harold Hallikainen wrote:

> I'm guessing this power supply only has a two wire line cord, right?

No, it's a 3-core all the way!

> Switchers have X capacitors across the line and Y capacitors line to
> chassis to attenutate conducted EMI. If the chassis is not grounded, the Y
> capacitors form a nice voltage divider, putting half the line voltage on
> the chassis. This is considered acceptable if the "leakage current" is low
> enough (in the neighborhood of 1mA, less for patient contact medical
> equipment). Your DVM, of course, drew considerably less than 1mA, so you
> were able to measure the unloaded voltage out of the voltage divider.

Right, but there is no chassis as such - the 0V output appears to be isolated from the Earth pin of the input 
(on a DC continuity test).  I can't imagine that they would put Y-capacitors from the Phase/Neutral to the 0V 
DC out unless it was also earthed.
 
> Even linear supplies with 50/60 Hz magnetics will have capacity to ground
> between the primary and the core. This will place a voltage on the
> chassis. Again, leakage current is the concern.

I suppose it's possible that the Earth pin is not connected inside, but I can't get inside without destroying 
it, and I don't know anyone with an X-ray machine :-)
 
Cheers,


Howard Winter
St.Albans, England


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