SIRIUS 3RT1 Contactors with Failsafe Control Siemens SIRIUS 3RT1 Contactors with Failsafe Control differ from other contactors by including safe wiring to the top. 3RT1 offers a power range from 55kW to 250kW in Sizes S6 to S12, enriching the SIRIUS modular system for safety solutions. Siemens 3RT1 Contactors feature an integrated failsafe PLC-input, resolving the problem of big contactors being unable to connect directly to the outputs of a failsafe PLC.