Siemens 3RB2163-4MC2 SIRIUS 3RB electronic overload relays. Siemens 3RB2163-4MC2 is the exact printed commercial reference for an electronic overload relay in the SIRIUS 3RB Overload Relays range. Siemens' official product description is: Overload relay 160...630 A for motor protection Size S10/S12, CLASS 5...30E Contactor mounting/stand-alone installation Main circuit: busbar connection Auxiliary circuit: Screw terminal Manual-Automatic-Reset Internal ground fault detection.