So we must not have a current flowing in the protective earth (PE), except for an accident, because:
1) the shields would be at a different potential, and
2) it would destroy the electro-magnetic compability.
But why are this to things dangerous?
Dear Mr. Bergweiler, a different potential on both sides of a shield will produce current. Every wire has a transfer impedance where the current on the shield is related to the voltage it induces on the inner signal wires. So a current on your shielding will produce noise in your measurement.
This is also related to the first Expert talk. If the metal where a strain gauge is positioned has a different potential than the amplifier it will produce also noise. Connecting metal and ampifier to PE reduces the noise only if there is no current on the PE line.
If you refer with 'dangerous' to electrical hazards, there is no Problem at all. You do not have to seperate N and PE to eneable the function of protected earth to keep persons save. Of course, for a R.C.B. it is necessary.
I was talking only about the electro-magnetic compatibility and preventing noisy signals and not about electrical hazards.
Well done. Gerne mehr davon :)
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