What it is and where it fits
The Siemens 3RT2028-1BF44 is a SIRIUS power contactor in the Size S0 frame, designed for switching motor loads and resistive circuits in industrial control panels. It mounts onto 35 mm DIN rail per DIN EN 60715 via screw and snap-on fastening, and accepts screw-type terminals for the magnet coil and main contacts. Rated coil voltage is 110 V AC, with a pickup threshold of 0.8 x rated value and a dropout at 1.1 x full-scale value — meaning the coil reliably pulls in above 88 V and releases above 121 V, a standard margin for industrial AC control circuits.
Switching duty and thermal limits
Maximum switching frequency depends on the duty category: 1 000 operations per hour at AC-1 (resistive), 750/h at AC-2 and AC-3 (motor starting/running), and 250/h at AC-4 (plugging/inching). The AC-3e rating also allows 750/h. These limits govern the contactor's thermal endurance — exceeding them shortens life or risks contact welding. Operating ambient temperature spans -25 °C to +60 °C; storage range is -55 °C to +80 °C. The storage limit governs handling and warehousing, not running conditions.
Panel integration and clearances
Dimensions: 85 mm high, 45 mm wide, 151 mm deep. Required clearance around the contactor: 10 mm upwards, 10 mm forwards, 10 mm downwards, and 6 mm at the sides. These spacings ensure adequate ventilation and arc-quenching volume — critical when grouping multiple contactors on a DIN rail. Mounting position is flexible: ±180° rotation on a vertical surface, and ±22.5° tilt forward/backward. This allows panel builders to orient the contactor for best wire routing without derating, as long as the clearance envelope is respected.
Wiring and auxiliary contacts
Main contact terminals accept solid or stranded wire from 1 to 10 mm², with dual-wire capability: 2 x (0.5 to 1.5 mm²) or 2 x (0.75 to 2.5 mm²). No auxiliary switch is included on this variant — if auxiliary contacts are needed, order a separate side-mount block. Mechanical life is rated at 10 million operations typical, reflecting the S0 frame's endurance for high-cycle applications like conveyor or pump control.