The Siemens 3RB1025-2QB0 is an electronic overload relay in the SIRIUS 3RB series, rated 6...25 A with class 20 trip curve, screw terminals, manual reset only, and size S0 footprint for direct contactor mounting.
The 6...25 A range covers motor FLA for small to mid-size induction motors — think 5.5 kW to 11 kW at 400 V three-phase. Class 20 means the relay allows up to 20 seconds at 600% of set current before tripping, matching standard motor start profiles for pumps, fans, and compressors. Manual reset only: once tripped, a local pushbutton must be pressed to reclose the N/C contact in the control circuit — no automatic restart, which is preferred for unattended or safety-monitored lines where unexpected re-energization is a hazard.
Size S0 is the standard Siemens contactor-mount footprint for this current class. The relay clips directly onto the matching S0 contactor (e.g., 3RT20 series), saving DIN-rail space and eliminating separate wiring between contactor and overload. Screw terminals accept 0.5...4 mm² stranded or solid — strip 8 mm, torque to 0.8...1.2 Nm. No auxiliary power supply needed; the relay is self-powered from the CTs on the motor leads.