What it is and where it fits
The Siemens 3RT2028-1BW40 is a SIRIUS power contactor in the S0 frame size, designed for switching loads in industrial control panels. It mounts via screw and snap-on onto a 35 mm DIN rail per DIN EN 60715, so it integrates into standard panel layouts without extra bracketry. The coil is rated 48 VDC, with a pickup threshold of 0.8 x rated value. The magnet coil termination is screw-type.
Key ratings and what they mean for your circuit
For DC-13 duty (solenoid loads), the contactor switches 10 A at 24 V and 2 A at 48 V — that covers most DC brake coils and small solenoid valves in a 24 VDC control circuit. At 60 VDC the rating drops to 2 A, and at 110 VDC it's 1 A, so plan your load accordingly. The main contact rating for AC-1 allows up to 1,000 switching cycles per hour; for AC-3 it is 750 cycles per hour. The contactor includes an auxiliary switch, which saves adding a separate block for status feedback or interlocking in simple circuits.
Mounting and wiring details
The contactor accepts solid or stranded conductors from 1 to 10 mm² on the main contacts, and 2x (0.5 to 1.5 mm²) or 2x (0.75 to 2.5 mm²) on the auxiliary circuit. That covers most panel wiring from 14 AWG to 8 AWG. Clearance distances: 10 mm upwards, 10 mm forwards, 10 mm downwards, and 6 mm at the side. The mounting position allows +/-180° rotation on a vertical surface and +/-22.5° tilt forward/backward, which gives flexibility in tight enclosures. Dimensions: 45 mm wide, 85 mm high, 107 mm deep. The S0 frame is a compact footprint that fits alongside other SIRIUS devices on the same DIN rail.
Environmental limits
Operating temperature range is -25 to +60 °C; storage range is -55 to +80 °C. The storage limit governs handling and shipping, not running conditions.