The Siemens 3RA2115-0FE15-1FB4 is a SIRIUS direct on-line starter in Size S00, rated 120 kW at 400 V in AC-3 duty — that is the motor-switching current it handles under full load, so it is sized for a 3-phase induction motor up to that power class. It ships as a pre-assembled combination: the contactor (3RT2015-2FB41), the link module (3RA2911-2AA00), and the circuit-breaker (3RV2011-0FA25) are supplied together, so you are not piecing three separate components for a standard motor feeder.
The width is the critical panel-pitch dimension: at 45 mm it occupies one standard 45 mm slot on a DIN-rail assembly, matching the footprint of other S00 feeders. Clearance requirements: 50 mm upwards, 20 mm forwards, 20 mm at the side, 10 mm downwards, and 0 mm backwards — the zero backward clearance means it can sit flush against a back panel or enclosure wall. Main current circuit uses spring-loaded terminals (cage-clamp style), which speeds wiring compared to screw terminals and resists loosening under vibration — relevant for machine-mounted sub-panels.