Double check your power stips and house wiring.

I had a machine connected through a 50ft cable and a powerstrip which
was tingly.  Turns out the ground wire was broken _inside_ the
powerstrip.

Usually this is due to bad ground.  Worse is when someone at a school
cut off the ground wire of the AV cart.  Plug it in backwards, and
it's ok.  Now connect the RF to the school cable system, and suddenly
everyone else sees 120V on the ground of the cable system.  I suspect
a better cable system (well grounded, etc) would have mitigated the
problem...

-Adam

On 1/5/06, Howard Winter <HDRW@h2org.demon.co.uk> wrote:
> 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
>
>
> --
> http://www.piclist.com PIC/SX FAQ & list archive
> View/change your membership options at
> http://mailman.mit.edu/mailman/listinfo/piclist
>

-- 
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist