What it is and what it does
The Siemens 3RU1126-1GB0 is a SIRIUS thermal overload relay, Size S0, designed to protect three-phase motor circuits against overload and phase failure. It mounts directly to a contactor — no separate base needed — and its Class 10 trip curve means it will open the control circuit within 10 seconds at 7.2× the set current, fast enough to protect standard induction motors during a stall or jam.
Key ratings and what they mean for your panel
Rated for a 3-pole main circuit with screw-type terminals that accept 2x (0.5... 1.5 mm²) solid or 2x (0.75... 2.5 mm²) stranded — common wire sizes for motor starters up to the S0 frame. The auxiliary and control circuit also uses screw terminals, same wire range. IP20 on the front means it's touch-safe for panel builders but not washdown-rated; keep it inside the enclosure. The relay occupies a 45 mm wide footprint on the DIN rail, 97 mm tall, 96 mm deep. Zero clearance needed upwards, forwards, backwards, or downwards — it can butt against other components without derating. Side clearance of 6 mm is required for heat dissipation; each pole dissipates 2.2 W at full load, so don't pack it tighter than that. Ambient operating range is -20 to +70 °C, storage and transport from -55 to +80 °C. It handles 100 % relative humidity (condensing) and shrugs off 8g shocks for 10 ms — fine for most industrial environments including conveyors and pumps.
Lifecycle and sourcing reality
It carries ATEX approval (DMT 98 ATEX G 001) for use in potentially explosive atmospheres, plus surge voltage resistance rated at 6 kV. The reference code per IEC 81346-2 is F, and RoHS compliance dates to July 1, 2006 — it's been RoHS-compliant since the directive took effect.
Mounting and integration
Fastens directly to a contactor via the contactor mounting method — no adapter plate. Mounting position allows vertical surface with ±135° rotation or ±45° tilt front-to-back, giving flexibility in tight cabinets. The S0 size is the most common frame for motor starters up to around 18.5 kW at 400 V.