Ok, because then a typical ground loop is formed, right?
In such a case the concept of soft grounding should be used, where no direct DC connection exists, but where the signal ground and enclosure are connected via a cap. This cap can be paralleled by a transzorb to prevent the develop of dangerous potentials and by a high ohmic resistance to allow a discharge of cap, when it can become charged somehow, by ESD or else.

The idea is to have no low ohmic connection for the mains frequencies which would otherwise create hum in the loop, but on the other hand to have the enclosure still working as a shield for the circuitry inside. Because of this the cap is urgently needed!

(We should briefly mention, that there are situations, where the signal ground MUST be connected to earthed enclosure even if this will cause hum loops, for instance when a safety class I transformer is used!)

Connecting signal ground and enclosure via a ferrite would just do the opposite: Creating a hum loop again and preventing the enclosure from working as a shield for the electronics inside. What a shitty alternative to the soft grounding scheme.


Yes, as a SAFETY path for eventual dangerous potentials. But not as the standard procedure, how to connect signal ground to enclosure.

Althoug it can be read in many tutorials, connecting the signal ground to enclosure via a ferrite is so wrong for me, I can't express! It stands in contradiction to everything I ever learned. To me this sounds: Let's cure a mistake by doing a second, in the hope that the two mistakes will cancel somehow...

Kai