Siemens 3RN1012-1CK00 Thermistor Motor Protector

Siemens 3RN1012-1CK00 Thermistor Motor Protector is a compact thermistor-based motor protection relay designed to monitor winding temperature and automatically trigger protective action when overheating is detected. As a standard evaluation unit, it offers Manual, Auto, and Remote operating modes and provides one normally open and one normally closed auxiliary contact for signaling and control with a contactor. The device is powered from a line voltage of either 110–120 V AC or 220–240 V AC via screw terminals, aligning with common control voltages. The 3RN1012-1CK00 is part of Siemens’ protective relay family and is documented as a phased-out product, with the preferred successor identified as 3RN2012-1BW30. Typically wired in the motor circuit to guard against thermal overload, this protector uses a thermistor input to monitor temperature and switches its auxiliary contacts to alert or disconnect the drive when safe operation would be compromised. Its design emphasizes straightforward screw-terminal connections for power and control, enabling reliable integration in three-phase motor installations where compact protection and simple signaling are required.