What it is and where it fits
The Siemens SIRIUS 3RT2028-2BW40 is a Size S0 power contactor with a spring-type coil terminal connection. It mounts via screw or snap-on onto 35 mm DIN rail per DIN EN 60715, and the mounting position allows +/-180° rotation on a vertical surface plus +/-22.5° tilt forward/backward — useful when panel layout is tight and the contactor must sit at an angle. Rated for AC-3 motor switching at up to 750 operating cycles per hour, and AC-4 inching/jogging at 250 cycles/h. The AC-1 resistive load maximum is 1 000 cycles/h. These duty-cycle limits define the contactor's thermal endurance — exceeding them shortens contact life, especially under AC-4 where arcing is heaviest. DC switching capability is specified at several voltages: 10 A at 24 V, 2 A at 48 V and 60 V, 1 A at 110 V, 0.9 A at 125 V, 0.3 A at 220 V, and 3 A at 400 V. These are the maximum make/break currents for DC loads — inductive loads (relays, solenoids) will need derating or arc-suppression, as DC arcs sustain longer than AC.
Integration notes
The contactor carries an auxiliary switch, so it can signal its state back to a PLC or safety relay without a separate add-on block. Main contact wire range accepts 1... 10 mm² solid or stranded, and the auxiliary contact terminals accept 2x (0.5... 2.5 mm²) solid or stranded — spring-cage on the coil side, screw-type on the main contacts. Clearance distances: 10 mm upwards, forwards, and downwards; 6 mm at the side. These are the minimum air gaps to grounded metal or adjacent devices — respect them to avoid flashover, especially in polluted environments. Operating temperature range -25... +60 °C; storage -55... +80 °C. The storage range is wider — handling, not running, is what that limit governs. Coil pick-up voltage is 0.8 x rated, drop-out typically below 0.6 x rated; the arcing time is 10... 10 ms and the DC operating time is 15... 17.5 ms.