What it is, what it does
The Siemens 3RT2035-1AT60 is a SIRIUS S2 power contactor — the workhorse for switching motor loads and resistive heaters in industrial control panels. It's the size that sits between the S0 compact and the S3 heavy-duty, so it handles the mid-range stuff without eating up DIN rail space. Rated for 40 A at 480 V, that's your AC-3 motor switching current; the contactor is sized for a 7.5 hp motor at 230 V, which lines up with a typical 5.5 kW induction motor on 400 V three-phase. Screw-type terminals on the magnet coil and main contacts — field-serviceable with a standard screwdriver, no special tooling needed.
Mounting and panel fit
Snaps onto 35 mm DIN rail per DIN EN 60715, or you can screw-mount it. The S2 form factor is 55 mm wide by 114 mm tall by 130 mm deep — that's a standard footprint that drops into most existing panels without shuffling other gear. Clearance around the sides is 6 mm; top and bottom need 10 mm for airflow and arc chutes. Mounting position is flexible: +/-180° rotation on a vertical surface, and you can tilt it forward or backward by +/-22.5°. That means you can fit it into tight enclosures where the rail isn't perfectly level, no problem.
Switching performance and thermal limits
Mechanical life is 10 million operations typical — that's the contactor itself, not the contacts under load. Electrical life depends on the duty cycle: AC-1 (resistive) gets 1,200 operations per hour max; AC-3 (motor start/run) is 1,000 ops/h; AC-4 (plugging/inching) drops to 300 ops/h. The arcing time is 10–20 ms, and the closing time at AC is 10–18 ms. Operates from -25°C to +60°C ambient, and can be stored from -55°C to +80°C. So it'll run in a hot panel next to a drive, but if you're cycling it hard on AC-4 duty, you'll want to stay under the 300 ops/h ceiling to avoid welding the main contacts.