SIRIUS S0 direct starter — 29 A AC-3, Class 10, 24 VDC
The Siemens 3RA2120-4EE27-0BB4 is a SIRIUS direct (on-line) starter in size S0, combining a contactor and overload relay in one assembly for motor starting and protection. A Class 10 is the most common choice for general-purpose conveyors, pumps, and fans — it protects the motor without nuisance tripping on a normal start. The coil is rated 24 VDC, a standard control voltage for PLC-driven panels and safety circuits. The unit ships with the supplied contactor 3RT2027-2BB40 and link module 3RA2921-2AA00, meaning it arrives as a complete, pre-assembled starter — no separate wiring between contactor and overload.
Mounting and wiring — DIN rail, spring terminals, S0 footprint
The S0 size footprint is 45 mm wide × 107 mm deep × 243 mm tall — the width is the key panel-space constraint; at 45 mm it fits a standard 8-module DIN rail slot with room for adjacent devices. Clearance requirements: 50 mm upwards, 20 mm forwards, 20 mm at the side, 10 mm downwards, and zero backwards. The zero backwards clearance means it can sit flush against the back panel or a busbar without needing an air gap behind it. Main circuit connections use spring-loaded terminals — push-in or screwdriver-actuated, no re-torquing needed. This is faster for panel building than screw terminals and holds well under vibration.
Lifecycle and sourcing — current production, quoted to order
Operating ambient range is -20 to +60 °C, with storage and transport range from -50 to +80 °C.