Siemens 3SB3 500-4MR01 Round Actuator Key Switch

Siemens 3SB3 500-4MR01 Round Actuator Key Switch is a key-operated switch in the SIRIUS 3SB3 family designed for panel-mounted control in industrial equipment. It uses a round actuator and accepts standard 3SB3 contact blocks to define its electrical function; in the standard version, two contact blocks can be snapped onto the actuator to create multiple circuit configurations. For lockable operation with a key, it is common to use the 3SB3901-0AC holder with pressure plates, enabling secure key control of the switch. The 3SB3 line is part of Siemens' Sirius command and signaling devices, with a long tradition of use in machine control and safety interlocks, and the 3SU1 SIRIUS ACT series identified as the successor for many 3SB3 configurations. This model's part number indicates a specific variant within the 3SB3 range, so it should be paired with compatible contact blocks and holders to achieve the desired number of poles and switching states. Typical applications include enabling machine start/stop or mode selection via a keyed actuation, or providing a secure interlock point in control panels where operator authorization is required.