What it is and what it does
The Siemens SIRIUS 3RU2136-4BB0 is a Size S2 thermal overload relay with a CLASS 10 trip curve, rated for main circuits up to 690 V. It mounts directly to a contactor and provides motor protection by monitoring current and tripping on overload. The integrated auxiliary switch signals a tripped condition — the part carries a "for message 'Tripped'" note, meaning the auxiliary contacts change state when the relay operates.
Key ratings and what they mean for fit
The relay is rated for motor loads at several voltages: 7.5 kW at 400 V, 11 kW at 500 V, and 15 kW at 690 V. At 480 V and 600 V the continuous current rating is 20 A. The auxiliary contacts are rated for switching at common control voltages: 2 A at 24 V, 3 A at 120 V, 2 A at 230 V, 1 A at 400 V, and 0.75 A at 690 V. These ratings define the maximum load the relay can protect and the signal it can pass back to a PLC or indicator.
Mounting and wiring
Fastening method is contactor mounting — it clips directly onto the matching contactor without extra hardware. The main circuit uses screw-type terminals accepting 2x (0.5 to 1.5 mm²) or 2x (0.75 to 2.5 mm²) solid or stranded wire. For the main contacts, a Pozidriv PZ 2 tip with a shaft diameter of 5 to 6 mm is specified. Dimensions: 55 mm wide, 90 mm high, 105 mm deep. Mounting position is any, and temperature compensation is active from -40 to +60 °C.