The Siemens 3RU2126-1CB0-ZX95 is a SIRIUS thermal overload relay, Size S0, with CLASS 10 trip protection — it opens the motor circuit within 10 seconds under a locked-rotor condition, sized for standard induction motors up to the relay's rated current range. It mounts directly onto a contactor, saving DIN-rail space in the panel.
The Size S0 footprint (85 mm deep, 45 mm wide, 85 mm tall) fits the standard S0 contactor interface; you can snap it onto a SIRIUS contactor without extra brackets. The auxiliary contacts are rated 3 A at 120 V and 2 A at 24 V, which covers most PLC input or indicator lamp loads. The integrated auxiliary switch means you don't need a separate add-on block for the trip signal.