What It Is and Where It Fits
The Siemens 3RB2025-1QB0 is a SIRIUS solid-state overload relay, designed to protect three-phase AC motors against overcurrent and phase imbalance. It mounts directly onto a contactor (contactor mounting), saving DIN-rail space in a motor control center or panel. Trip class CLASS 10E means it will trip within 10 seconds at a locked-rotor current of 7.2× setting, suitable for standard induction motor starts — pumps, fans, compressors — without nuisance tripping during acceleration. The front face carries IP20 protection, so it's safe for finger-probe access inside an enclosed panel, but not for washdown environments.
Key Ratings and What They Mean for Your Panel
Three poles handle the main current circuit, with screw-type terminals accepting solid conductors from 0.5 to 4 mm² (or 2× 0.5 to 2.5 mm²), and finely stranded with ferrules down to 0.5 mm². That covers most control-circuit and small-motor power wiring up to about 4 kW at 400 V. Maximum AC-3 rated voltage is 690 V, so it's compatible with 400 V and 690 V three-phase networks common in European industrial installations. Surge voltage resistance is rated at 6 kV, and burst immunity meets IEC 61000-4-4 severity level 3 (2 kV on power ports, 1 kV on signal ports). This means it will tolerate typical switching transients from contactors and drives in the same cabinet without false tripping. Operating temperature range is -25 to +60 °C, with storage/transport from -40 to +80 °C. Shock resistance of 15g for 11 ms covers most vibration profiles in fixed industrial machinery.
Compliance and Sourcing Reality
For a BOM freeze or validation project, this part is fully traceable under Siemens change control. The reference code per DIN EN 81346-2 is F (protective device), which aligns with standard IEC 81346 labeling for panel documentation.
Physical Integration Notes
Dimensions are 45 mm wide, 73 mm high, 75 mm deep. Clearance required: 0 mm upwards, forwards, backwards, and downwards; 6 mm at the side. This fits a standard 45 mm-wide contactor footprint with zero-gap stacking vertically. Mounting position is any orientation, which simplifies panel layout when space is tight.