What it is and what it does
The Siemens SIRIUS 3RU2136-4FD0 is a thermal overload relay, size S2, designed for motor protection in industrial control panels. It mounts directly onto a contactor and provides CLASS 10 trip protection, meaning it will trip within 10 seconds at 7.2× the set current — fast enough for standard motor start-up curves without nuisance tripping. Rated for 690 V, it handles motor loads up to 18.5 kW at 400 V and 37 kW at 690 V. The auxiliary switch is integrated, and the overload release is thermal with temperature compensation from -40 to +60 °C, so it stays accurate across typical plant-floor conditions.
Mounting and integration
Fastens directly to the contactor (contactor mounting), no DIN rail required. Dimensions: 55 mm wide, 90 mm high, 105 mm deep — fits standard S2 footprint. Screw-type terminals for the main circuit; accepts 2× (0.5 to 2.5 mm²) solid or stranded wire. Use a Pozidriv PZ 2 tip, shaft diameter 5–6 mm. Mountable in any position, and the operating frequency range is 50–60 Hz, so it works on both 50 Hz and 60 Hz supplies without derating.