The Siemens 3RA2120-4CH27-0BB4 is a SIRIUS direct (on-line) starter in Size S0, combining a contactor and overload relay into one unit that snaps onto 60 mm busbar systems. Its AC-3 rating of 22 A at 400 V means it switches three-phase motor loads up to that current under full-load starts — typical for conveyors, pumps, and fans in a control panel. The Trip Class 10 overload curve trips within 10 seconds at 7.2× rated current, protecting standard induction motors during stall or jam conditions without nuisance tripping on normal acceleration.
Rated 22 A in AC-3 at 400 V, with a maximum operating voltage of 690 V AC-3. The 24 V control coil keeps it compatible with standard PLC output cards or control transformers. The starter is designed for vertical mounting and needs 50 mm clearance upwards, 20 mm forwards, 10 mm downwards, and 20 mm at the side (–). That 260 mm height and 45 mm width fit a standard 60 mm busbar footprint without crowding adjacent feeders.