What it is and what it does
The Siemens 3RU2136-4GB1 is a SIRIUS thermal overload relay, size S2, designed to protect three-phase motors against overload and phase failure. It trips on a CLASS 10 curve — meaning it will open the contactor within 10 seconds at a locked-rotor current seven times the full-load setting. That's the curve you want for standard induction motors driving pumps, fans, or conveyors where the start-up time is short. The relay is rated for main circuits up to 690 V, and at 400 V it handles 22 kW motor loads. It carries a 45 A rating at 480 V and 600 V, and 37 kW at 690 V. The auxiliary contacts are rated for 2 A at 24 V, 3 A at 120 V, and 1 A at 400 V — enough to signal a PLC input or a status lamp.
Mounting and wiring
This relay is designed for stand-alone installation — it does not require a dedicated base or adapter. It mounts in any position, which helps when you're fitting it into a tight panel. The main circuit terminals accept screw-type connections, and the terminal screws take a Pozidriv PZ2 bit or a 5–6 mm diameter shaft. Wire sizes from 0.5 to 2.5 mm² (solid or stranded) are accommodated, with two conductors per clamp. Dimensions are 55 mm wide, 105 mm tall, and 117 mm deep — a compact footprint for a size S2 relay, so it fits in a standard 55 mm DIN-rail slot if you're using an adapter base (not included). The auxiliary switch is integrated into the housing, no extra module needed.
Environmental and compliance
Operating temperature range is –40 to +70 °C, with storage and transport limits from –55 to +80 °C. Temperature compensation is active from –40 to +60 °C, so the trip curve stays accurate across the working range. The relay is RoHS compliant with a substance prohibition date of October 15, 2014.