The Siemens 3RU7126-1DB0 is a SIRIUS S0-size thermal overload relay, designed to protect three-phase AC motors against overload and phase failure by monitoring the motor current and tripping the associated contactor when the current exceeds the setpoint for too long. The relay is rated for a continuous operational current of 3.2 A at up to 690 V AC/DC, 50/60 Hz, and it mounts directly onto a matching S0 contactor (e.g., the 3RT10 series), saving panel space and wiring.
This relay is sized for the S0 contactor frame — it fastens directly onto the contactor via the contactor mounting method, eliminating separate DIN-rail space and reducing wiring between the contactor and overload. The main circuit uses screw-type terminals on top and bottom, accepting 2× (0.5 to 1.5 mm²) solid/stranded or 2× (0.75 to 2.5 mm²) finely stranded with ferrules, with a tightening torque of 2 to 2.5 N·m. Auxiliary and control circuit terminals are also screw-type, torqued to 0.8 to 1.2 N·m. The auxiliary contacts are rated at 3 A at 24 V and 2 A at 230 V, with a DC-13 rating of 1 A at 24 V for the control circuit. The enclosure is rated IP20 on the front and at the terminals, suitable for installation inside a control cabinet that provides the environmental seal.