The Siemens 3RB1026-1QB0 is a solid-state overload relay from the SIRIUS 3RB family, rated for a motor full-load current range of 6...25 A with a Class 10 trip characteristic. The 6...25 A window covers common small-to-medium motor frames (IE2/IE3 up to about 11 kW at 400 V). It mounts directly onto a contactor of size S0, using screw terminals for the power and control wiring. The manual-automatic reset selector lets the panel builder choose between a latched trip that needs a button push (safer for unattended lines) and an auto-reset that restarts after the thermal model cools (acceptable for remote or hard-to-access equipment).
Size S0 is the standard Siemens contactor frame for currents up to about 40 A AC-3. The 3RB1026-1QB0 clips onto the contactor's mounting surface, sharing the same DIN-rail or screw-panel footprint. No extra panel space is needed beyond the contactor itself. The screw terminals accept up to 4 mm² stranded wire; torque to the value printed on the relay housing.