The Siemens 3RU2126-4CC0 is a SIRIUS thermal overload relay in size S0, designed to protect motors against overload and phase failure. It mounts directly to a contactor (contactor mounting) and uses spring-loaded terminals for the main circuit. The CLASS 10 trip class means it will trip within 10 seconds at 7.2× the set current — standard for standard-duty motor starting, not for high-inertia loads that need CLASS 20 or 30.
Ratings and what they mean for fit
Rated voltage is 690 V, with AC-3e switching rated up to that same 690 V. At 400 V it handles 11 kW; at 480 V and 600 V it carries 22 A; at 690 V it handles 18.5 kW. The auxiliary switch is integrated — no add-on block needed for a remote trip signal. The thermal release design compensates for ambient temperature from -40 to +60 °C, so it won't nuisance-trip in a hot panel or cold warehouse.
Integration notes
Mounts in any position on a contactor (contactor mounting). Spring-loaded terminals accept 2 × (0.5 to 2.5 mm²) solid or stranded wire. The screwdriver shaft diameter is 3 mm; tip size is 3.0 × 0.5 mm. Depth is 84 mm, width 45 mm, height 102 mm — fits standard S0 footprint panels.