The headline AC-4 rating of 55 A at 400 V tells you it can handle reversing, inching, and plugging duty — the toughest switching profile for a contactor, where it makes and breaks motor current at full locked-rotor levels. That 55 A AC-4 number is the one that governs real motor-reversing applications, not a higher AC-3 figure. The 37 kW rating at 500 V gives the sizing for standard induction motors on a 500 V line. The contactor carries an IP20 rating on the front with a cover or box terminal, meaning it's protected against finger contact from the front once installed in an enclosure. The terminal area itself is IP00, so live parts are exposed during wiring — standard for panel-mount gear.
Snap-on mounting onto 35 mm or 75 mm standard DIN rail, or screw-fasten directly. The S3 footprint is 70 mm wide by 146 mm high by 139 mm deep — check your rail clearance and gland-plate depth, especially if you're retrofitting into a panel originally laid out for a smaller frame. Solid conductors: 2x (0.5 to 1.5 mm²), 2x (0.75 to 2.5 mm²), max 2x (0.75 to 4 mm²). Stranded: 2x (10 to 50 mm²). That's a wide range — you can land both control-circuit fine wires and power-circuit heavy cables on the same block.