What it is and what it does
The Siemens 3RU2136-4RB1 is a SIRIUS thermal overload relay — size S2, designed for stand-alone installation with screw-type terminals on the main current circuit. It protects motors against overload by monitoring current and tripping on a CLASS 10A curve, meaning it will open within 10 seconds at 7.2× the set current, which is the standard for standard-duty induction motors (pumps, fans, compressors). The integrated auxiliary switch signals the tripped state — the part's note field reads "for message 'Tripped'" — so a PLC or annunciator gets a clean digital indication when the relay has operated.
Key ratings and what they mean for fit
Rated insulation voltage is 690 V, with AC-3e switching capability up to that same voltage. At 400 V it carries 37 kW motor load; at 690 V that rises to 75 kW. The auxiliary contact ratings cover a wide control-voltage range — 2 A at 24 V, 3 A at 120 V, 2 A at 230 V, 1 A at 400 V, 0.75 A at 690 V — so it can directly drive a PLC input or a contactor coil without an interposing relay in most panels. Per-pole power dissipation is 6.3 W, which matters for enclosure heat buildup if the relay is grouped with other devices.
Mounting and wiring
Mounts in any position — no derating for sideways or inverted installation. Dimensions are 55 mm wide, 105 mm high, 117 mm deep, so it fits a standard 55 mm-wide DIN-rail footprint (S2 frame). Main circuit terminals accept 2× (0.5 to 1.5 mm²) solid or stranded, or 2× (0.75 to 2.5 mm²); use a Pozidriv PZ 2 screwdriver with a 5–6 mm shaft diameter. The M6 main-contact bolts are sized for the S2 current range. Temperature compensation is active from -40 °C to +60 °C, so the trip curve stays accurate even in an unheated enclosure.