What it is and what it does
The Siemens 3RU2136-4GD1 is a SIRIUS thermal overload relay, size S2, designed to protect motors against overload and phase failure. It's the part that sits between the contactor and the motor, monitoring current and tripping on a CLASS 10 curve — meaning it opens in under 10 seconds at 7.2× the set current, which is the standard for standard-duty induction motors like pumps and fans. Rated for 690 V and delivering 22 kW at 400 V (45 A at 480 V, 30 kW at 500 V, 37 kW at 690 V), this relay covers a solid mid-range motor protection slot. The thermal bimetallic release is temperature-compensated from -40 to +60 °C, so it doesn't nuisance-trip when the panel warms up in summer.
Mounting and wiring reality
Stand-alone installation — no DIN-rail clip on this S2 frame. You bolt it directly to the mounting plate or panel using the M6 main contact screws. Mounting position is any, which helps in tight retrofit cabinets. Main circuit wiring lands on screw-type terminals accepting 2× (0.5 to 2.5 mm²) solid or stranded. The integrated auxiliary switch handles the signal side — rated 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. That auxiliary contact is what tells the PLC or contactor coil that the relay has tripped. Pozidriv PZ 2 screwdriver tip, shaft diameter 5 to 6 mm — standard electrician's kit, no special tooling needed.
Lifecycle and sourcing posture
Current production — no end-of-life notice on this 3RU2136-4GD1. The SIRIUS platform is Siemens' mainstream motor protection line, so spares and replacements are stable for the foreseeable future. Substance prohibitance date of October 15, 2014, means the part meets RoHS and REACH requirements from that compliance cutover. No additional documentation beyond the standard declaration is expected for this generation.
What the ratings mean for your BOM line
The CLASS 10 trip class is the key selection parameter: it matches the thermal capacity of standard squirrel-cage motors. If your motor has a higher inertia load (centrifuge, crusher) you'd need CLASS 20 or 30 — this relay isn't that. Per-pole power dissipation of 5.2 W adds up in a multi-motor panel. Three poles running at full load dump about 15.6 W into the enclosure — factor that into your thermal budget if the panel is sealed. The note "for message 'Tripped'" on the product line refers to the auxiliary contact position that signals the tripped state — it's the normally-open contact that closes when the bimetals have bent far enough. That's what you wire back to the PLC input or the contactor's undervoltage release.