What the 3RT2035-3AN20 is and what it does
The Siemens 3RT2035-3AN20 is a SIRIUS power contactor in the S2 frame size, designed to switch motor loads in industrial control panels. Its headline rating is 40 A at 480 V and 7.5 hp at 230 V, which means it can handle a 7.5 hp motor on a 230 V supply or a larger motor at 480 V, up to that current limit. The contactor uses spring-type terminals on the magnet coil, accepting 2x (0.5... 2.5 mm²) solid or stranded wire, so termination is tool-less and vibration-resistant — a real time-saver on a panel build. It mounts via screw and snap-on onto 35 mm DIN rail per DIN EN 60715, and the mounting position allows +/-180° rotation on a vertical surface, plus +/-22.5° tilt forward and backward. That flexibility matters when you're squeezing contactors into a crowded enclosure — you can orient it to match the cable entry. Operating temperature range is -25 to +60 °C, storage goes -55 to +80 °C, so it's fine for most indoor panel environments. Mechanical life is rated at 10,000,000 cycles typical, and the contactor carries an auxiliary switch. Switching frequency limits are 1,200 cycles/h at AC-1, 1,000 at AC-3, and 300 at AC-4 — the AC-4 figure is the one to watch for plugging or inching duty, where you'll need to derate the application.
Key ratings and what they mean for fit
The 40 A at 480 V rating is the thermal current — it tells you the contactor can carry that current continuously in a resistive load. But for motor switching, the AC-3 rating is what governs: the contactor is sized for a 7.5 hp motor at 230 V, which translates to roughly 22 A at that voltage. If your motor plate says 10 hp at 230 V, this contactor is undersized — step up to the next SIRIUS frame. The AC-4 switching frequency of 300 cycles/h is the hard limit for reversing or jogging applications; exceeding it shortens contact life fast. Dimensions are 130 mm depth, 55 mm width, and 114 mm height. The 55 mm width is the key panel-space figure — it's the same footprint as other S2 contactors, so swapping within the family is a drop-in. Clearance requirements: 10 mm upwards, forwards, and downwards, and 6 mm at the side. That's tight enough for dense rail packing.