What this SIRIUS direct starter is
The Siemens 3RA2120-4AH26-0BB4 is a SIRIUS direct-on-line starter in the S0 size — a pre-assembled combination of a contactor and a circuit-breaker in one unit, ready to snap onto a 60 mm busbar system. It ships with a 3RT2026-2BB40 contactor and a 3RA2921-2AA00 link module already integrated, so you don't have to piece together the motor-starting branch yourself.
Mounts on 60 mm busbars — panel fit dimensions
Designed for snapping onto 60 mm busbar systems, with a vertical mounting position and spring-loaded terminals for the main circuit. The envelope is 45 mm wide, 260 mm tall, and 165 mm deep — that's the S0 footprint, so it fits alongside other S0 feeders on the same busbar. Clearance requirements: 50 mm upward, 20 mm forward, 20 mm at the sides, and 10 mm downward. Zero clearance needed backward — the back of the unit sits flush against the busbar support.