What this contactor is and what it handles
The Siemens SIRIUS 3RT1035-1AH28-0PA4 is a size S2 power contactor rated for motor switching up to 22 kW at 500 V in AC-3 duty, and 18.5 kW at 400 V in AC-2 duty. That AC-3 rating is the one that matters for standard three-phase induction motors — it tells you the contactor can make and break the motor's locked-rotor current without welding the main contacts. The AC-2 rating covers slip-ring motors where the inrush is lower but the switching frequency is higher. It sits in the SIRIUS family, Siemens' modular contactor range for panel builders. The S2 frame is the mid-size in the line, balancing current capacity with panel space: 65 mm wide, 112 mm high, 115 mm deep. That depth is a key dimension for enclosure depth planning — it's the distance from the DIN rail to the furthest projection of the terminals.
Mounting and wiring fit
Mounts on 35 mm DIN rail per EN 50022 using the integrated snap-on latch, or with screws through the base. Side-by-side mounting is allowed, so you can gang contactors without a gap — useful when building a motor control center section. The front face carries an IP20 rating, meaning finger-safe when installed in an enclosure; the terminal area itself is IP00, so live parts are exposed until the enclosure door is closed. Main circuit connections are screw-type terminals. Solid conductors: two per clamp, from 0.5 mm² up to 4 mm². Stranded: two per clamp, from 0.75 mm² up to 25 mm². That 25 mm² stranded capacity is generous for a contactor this size — it matches the cable needed for the 22 kW rating without needing a terminal reducer.
Environmental and endurance specs
Rated for pollution degree 3, so it's suited for industrial environments with conductive dust or intermittent condensation. Operating temperature range is -25 to +60 °C; storage range is -55 to +80 °C. The mechanical endurance is 10 million operations — that's the contactor body, not the contacts under load. For the electrical life, the maximum switching frequency varies by duty: 1200 cycles per hour in AC-1 (resistive loads), 1000 in AC-3 (squirrel-cage motors), and 300 in AC-4 (plugging/inching). The AC-3 figure is the one to plan around for a conveyor or pump cycling every few seconds.