Power supply musings

[Ingo Debus]

Rene Schmitz wrote:
> I do it the same way. To add safety when the gear is NOT connected to other
> devices (at least one of which must have a connection between circuit and
> power gnd) you can place a small neon bulb between circuit and mains gnd.
> The bulb is a perfect insulator at small voltages, however a voltage of
> about 65V will make it conduct, and relatively low ohmic (sp?).

OH NO!! DON'T DO THAT!! ==:-O

(This nonsense was in Elektor, wasn't it?) You really cannot rely on
that there is a ground fault interrupter (or FI, or RCD). So this tiny
bulb has to carry really high current until the fuse blows. How do you
know that it isn't destructed first?

Also, the ground connection via audio shields has nothing to do with
safety. Safety ground must not be interruptable (via plug) and the gauge
must be heavy enough to carry the short-circuit current. Both conditions
are usually not met with audio shields.

On the other hand, as far as I know (but I'm not completely sure) the
circuit ground doesn't need to be connected to Protective Earth (PE). At
the Yamaha DX7II I once had, it wasn't.

Ingo