The Siemens 3RU7136-4DB0 is a SIRIUS thermal overload relay in the S2 frame size, rated for a continuous operational current of 25 A and a trip class of Class 10. It mounts directly onto a contactor of the same S2 size, protecting a three-phase motor circuit against sustained overloads by sensing the heat generated in the bimetallic strip.
The 25 A rated current sets the maximum continuous load the relay can carry without nuisance tripping; for a motor circuit, you size the relay to the motor's full-load amps, typically 1.0 to 1.05× FLA. The S2 frame is the mechanical envelope; it physically matches the S2 contactor footprint, so the relay clips onto the contactor without extra brackets. The relay accepts screw-type terminals for both the main and auxiliary circuits. Wire range is 2× (0.5 to 1.5 mm²) solid or stranded, or 2× (0.75 to 2.5 mm²). Terminal torque for the main circuit is 3 to 4.5 N·m; for auxiliary contacts, 0.8 to 1.2 N·m.
Side spacing to grounded parts must be at least 6 mm.