What this relay does and where it fits
The Siemens 3RU2126-4AJ0 is a SIRIUS thermal overload relay in Size S0, Trip Class 10, designed to protect motors against overload and phase failure. It mounts directly onto a contactor — no separate base needed — and integrates into a standard DIN-rail panel layout. Trip Class 10 means it will trip within 10 seconds at 7.2× the current setting, which is the standard for standard-duty induction motors (pumps, fans, compressors). For motors with longer starting times (high-inertia loads), a Class 20 or 30 relay would be needed instead. Rated motor power: 7.5 kW at 400 V, 7.5 kW at 500 V, 11 kW at 690 V. The auxiliary contact block is integrated, with ratings ranging from 2 A at 24 V up to 3 A at 120 V and 1 A at 400 V.
Mounting and wiring notes
Fastens directly to a contactor (contactor mounting). The main circuit connection uses ring cable lugs with M4 screws. The auxiliary switch is integrated — no add-on block required. Screwdriver tip: Pozidriv PZ2, shaft diameter 5–6 mm. Dimensions: 45 mm wide, 85 mm high, 85 mm deep — fits the S0 footprint. Mounting position: any. Temperature compensation is active from -40 to +60 °C.
Compliance and environmental
Substance prohibitance date (RoHS-like) is 10/01/2009, indicating compliance with EU substance restrictions. Storage and transport temperature range: -55 to +80 °C; operating: -40 to +70 °C.