What it is and where it fits
The Siemens 3RT2028-1NB30 is a SIRIUS power contactor in the S0 frame size, designed for switching motor loads in control panels. It mounts on 35 mm DIN rail per DIN EN 60715 using screw or snap-on fastening, and accepts solid or stranded conductors from 1 to 10 mm² on the main contacts. The coil is rated 21 to 28 VDC with a 24 V rated-value pickup current of 10 A and an inrush peak of 3 A. The magnet coil uses screw-type terminals, and an auxiliary switch is built in. Mechanical life is typical at 10 million operations. Maximum switching rates are 1 000 cycles/hour under AC-1 (resistive load), 750 cycles/hour under AC-3 (motor starting), and 250 cycles/hour under AC-4 (plugging/inching).
Mounting and panel integration
The S0 contactor footprint is 45 mm wide × 85 mm high × 107 mm deep. Clearance requirements: 10 mm upward, 10 mm downward, 10 mm forward, 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° on a vertical surface. Operating temperature range is -25 to +60 °C; storage range is -55 to +80 °C. This covers most indoor panel environments without forced derating.
What the ratings mean for fit
The AC-3 switching rate of 750 cycles/hour tells you this contactor is sized for frequent motor starting — typical for conveyors, pumps, and fans in a production line. The AC-1 rate of 1 000 cycles/hour covers resistive heater or lighting loads. The AC-4 rate of 250 cycles/hour limits plugging and inching duty; if your application requires frequent reversing or jogging, stay within that envelope. The coil holding voltage range is 21 to 28 V. It stays pulled in through dips down to 21 V.