On Tue, 6 Dec 2005 08:06:58 +0100, "Meindert Sprang"
wrote:

I have quite a lot of experience with power supply modules (the "open frame
type") and I dear say that for instance NONE of the types offered in the
Farnell catalog have their - or 0 connected to the PE. From a manufacturer's
point of view this would be absolutely stupid because it means that he would
have to have two types of each model, one with the + to PE and another with
the - to PE. Also in lab supplies you will always see an extra ground
terminal, often between the + and - and possibly with a supplied bracket
between the ground and -.

Besides, many applications need a complete separation from mains, even from
ground. So that is another reason for manufacturers not to connect the - to
PE(ground).

For any low level measurements, the PE is badly polluted by the noise
from switching mode power supply EMC filters etc. For this reason, a
separate technical earth (TE) network is often used with only a single
contact point between the neutral, grounding electrode and PE and TE
earths.

A single power supply with the DC side connected to PE would pollute
the whole TE network and you would very quickly get rid of such power
supplies.

Paul