KUHNKE Automation 5.5 Operative Earth / Protective Earth Connect operative earth/protective earth to the protective earth conductor of the switching cabinet or the system that the thermo-controller is installed in. Connection is made to the bolt on top of the device. The minimum cross section must be no less than 4 mm 2 if leads are laid in a non-protected manner. Try to keep the lead to the cabinet terminal as short as possible. A low-impedance earth conductor improves the dissipation of interference received via external power supply cables, signal cables or cables of periph- eral units. 22 E 774 GB 30.06.2014