SIRIUS direct starter — snaps onto 60 mm busbars
The Siemens SIRIUS 3RA2120-4BD27-0BB4 is a direct online (DOL) starter in the S0 feeder size, designed specifically for snapping onto 60 mm busbar systems — no DIN rail adapter needed, the housing clips directly to the busbar profile. It ships as a complete assembly with the supplied 3RT2027-1BB40 contactor and 3RA2921-1BA00 link module, so the overload relay and contactor are pre-wired and mechanically interlocked for the S0 frame.
Panel clearances and mounting constraints
The starter occupies 45 mm width, 260 mm height, and 165 mm depth. For thermal management and arc-flash clearance, Siemens specifies 50 mm upwards, 20 mm forwards, 10 mm downwards, and 20 mm at the side — zero clearance backwards since the busbar mounting face is the rear plane. Mounting position is vertical only. The main circuit uses screw-type terminals — torque to the values in the SIRIUS S0 manual for the 20 A rating. Operating ambient range is -20 to +60 °C, with storage and transport limits of -50 to +80 °C. The 24 V control coil is compensated across the full operating range.
Current production — quoted to order
Lifecycle status is current production — this is an active Siemens catalog line, not a phase-out or NRND part. No official successor is recorded because none is needed. Sourced through authorized distribution channels. The 24 V coil variant (this one) is a common voltage for PLC-driven panels — expect standard lead times for the S0 frame. RoHS compliance date is 2009-10-01 per the substance prohibition entry — the starter meets the original RoHS directive and subsequent amendments.