It's a 3-pole unit rated 90 A operational current at AC-3 duty (400 V), which is the motor-switching curve you care about for induction motors up to roughly 45 kW on a 400 V line. The magnetic short-circuit trip responds at 1170 A, so it clears a bolted fault fast without waiting for the thermal element.
The S3 footprint is 70 mm wide, 165 mm tall, 174 mm deep — that's a three-module-wide slot on the rail. Clearance needs: 50 mm above and below, 30 mm to the side, 167 mm forward. No rear clearance required. Terminal boxes accept up to 70 mm² stranded or 2/0 AWG, torqued to 4–6 N·m.
The headline number is 90 A at AC-3 / 400 V — that's the motor-switching current, not the resistive-heating rating. The instantaneous magnetic trip at 1170 A (about 13x In) lets it ride through motor inrush without nuisance tripping, but clears a phase-to-phase fault in under a cycle. Power loss is 30 W typical — factor that into enclosure thermal rise if you're packing several in a small cabinet. Shock resistance 25 g / 11 ms per IEC 60068-2-27 means it survives transport and moderate machine vibration.
RoHS compliance date is 2006-07-01, so it meets the EU directive. Rated impulse withstand voltage is 6 kV, and insulation voltage is 690 V at pollution degree 3 — that's the IEC 60947-2 coordination level for industrial panels. The SIRIUS series carries UL/CSA approvals for North American installations, though the specific listing is not detailed in this record. Expect standard IEC 60947-2 and UL 489 documentation from Siemens.