The Siemens 3RB2025-1QB0 is a SIRIUS solid-state overload relay, designed to protect three-phase AC motors against overcurrent and phase imbalance.
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. 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.
Dimensions are 45 mm wide, 73 mm high, 75 mm deep. This fits a standard 45 mm-wide contactor footprint with zero-gap stacking vertically.