SIRIUS S0 Power Contactor with 110 V AC Coil
The Siemens 3RT2028-2BF44 is a SIRIUS power contactor in the S0 frame size, designed for switching motor loads and resistive loads in industrial control panels. It is fitted with a 110 V AC coil and spring-type terminals for the magnet coil, and mounts via screw or snap-on onto a 35 mm DIN rail per DIN EN 60715. The contactor is rated for a main contact operating current of 18 to 8 A, and provides a mechanical service life of 10,000,000 operating cycles typical. Its coil operating range spans 0.8 to 1.1 times the rated value.
Switching Frequency and Duty Ratings
Maximum switching frequency depends on the duty category: 1,000 cycles/hour under AC-1 (resistive loads), 750 cycles/hour under AC-2 or AC-3 (slip-ring or squirrel-cage motors), 750 cycles/hour under AC-3e (enhanced motor starting), and 250 cycles/hour under AC-4 (plugging or inching). These limits govern thermal rise in the contactor — exceeding them accelerates contact wear, particularly under AC-4 where the arc energy is highest.
Mounting, Clearances, and Environmental Range
The contactor measures 45 mm wide, 102 mm high, and 154 mm deep. Minimum clearances to adjacent components are 10 mm upward, 10 mm forward, 10 mm downward, and 6 mm at the side. The mounting position allows +/-180° rotation on a vertical surface and can be tilted forward/backward by +/-22.5°, giving flexibility in tight enclosures. Operating temperature range is -25 to +60 °C; storage range is -55 to +80 °C. Conductor cross-sections accepted are 1 to 10 mm² solid or stranded, with 2x (0.5 to 2.5 mm²) for parallel wiring.
Auxiliary Contact Ratings and Switching Times
This variant ships without an auxiliary switch block. For auxiliary contact ratings at various voltages: 6 A at 24 V, 2 A at 48 V, 2 A at 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. The motor horsepower rating at 230 V is 5 hp. Switching times are 15 to 18 ms DC (likely the dropout delay) with an arcing time of 10 ms.