Kendrion Kuhnke Automation GmbH Hardware 4.1.1 Earthing Connect the Kuhnke FIO modules to earth by attaching the metal housing to functional earth. Since the functional earth connector dissipates HF currents, it is of utmost importance for the module's noise immunity. HF interference is dissipated from the electronics board to the metal housing. The metal housing therefore needs to be suitably connected to a functional earth connector. You will normally have to ensure that the connection between module housing and DIN rail conducts well, the switching cabinet is safely connected to earth.
the connection between DIN rail and switching cabinet conducts well, In special cases you may attach the earth wire straight to the module. F i Figure 4: Aluminium profile Kuhnke FIO CAM Control ( E 808 GB ) 15 11/10/2017 NOTE Earth wires should be short and have a large surface (copper mesh). Refer to http://de.wikipedia.org/wiki/ground (electronics) or a similar source for further details _