The Siemens 3RA2120-4NH27-0BB4 is a SIRIUS direct online starter, Size S0, rated 15 kW at 400 V in AC-3 duty — that is the motor-switching current for a 3-phase induction load up to that power. The unit ships as a pre-assembled combination: the supplied contactor is 3RT2027-2BB40, the circuit-breaker is 3RV2021-4NA20, the link module is 3RA2921-2AA00, and the busbar adapter is 8US1251-5NT11. All main and auxiliary/control connections use spring-loaded terminals — no screwdriver torque required, which speeds panel wiring and resists vibration loosening.
Designed for snapping onto 60 mm busbar systems, the starter mounts vertically and occupies a 45 mm wide footprint. The overall dimensions are 45 mm wide, 260 mm high, and 165 mm deep. Clearance requirements: 50 mm upwards, 20 mm forwards, 10 mm downwards, 20 mm at the side, and 0 mm backwards — so it can sit flush against a back panel.