SIRIUS S2 power contactor — what the ratings mean for your panel
The Siemens 3RT2035-3AL20-1AA0 is a SIRIUS-branded power contactor in size S2, designed for switching motor loads and resistive circuits in industrial control panels. Its headline rating of 40 A at 480 V AC-3 means it handles the inrush and breaking of three-phase induction motors up to that current — the AC-3 duty class covers starting and plugging, not just steady-state. At 230 V it carries 7.5 hp, which is the typical rating for a moderate pump or fan motor on a 230 V three-phase supply. The contactor mounts via screw or snap-on onto 35 mm DIN rail per DIN EN 60715, so it fits standard panel layouts without adapter plates. Spring-type terminals on the magnet coil speed wiring — no screwdriver needed for the coil connections, which matters when you're dressing multiple contactors in a row. The main contact configuration is 18...1, meaning it carries an integrated auxiliary switch block, so you don't need a separate side-mount for basic status feedback. Switching frequency varies by duty: 1 200 cycles/hour for AC-1 resistive loads, 1 000 for AC-3 motor duty, and 300 for AC-4 (plugging/reversing). If your application involves frequent jogging or reversing, the AC-4 limit is the one that governs contact life — plan around 300 ops/hour max.
Mounting and integration
Dimensions: 114 mm high, 55 mm wide, 130 mm deep. The S2 frame size is the mid-range in the SIRIUS contactor family — larger than the S0 (3RT2015/3RT2016) but smaller than the S3. Clearance requirements: 10 mm upwards, 10 mm forwards, 10 mm downwards, and 6 mm to the side. That 6 mm side gap is tighter than the vertical clearances, so when ganging contactors side-by-side on DIN rail, maintain that minimum for arc-flash venting and heat dissipation. Operating temperature range is -25 to +60 °C, storage from -55 to +80 °C. The operating range covers most indoor panel environments; if the panel sits near a furnace or in a desert enclosure, derate above 60 °C per the thermal curve.
DC switching capability — not just an AC contactor
While primarily an AC motor contactor, the 3RT2035-3AL20-1AA0 carries DC switching ratings that make it usable for DC load circuits in the same panel: 10 A at 24 V, 2 A at 48 V and 60 V, 1 A at 110 V, 0.9 A at 125 V, 0.3 A at 220 V, 3 A at 400 V, and 0.6 A at 440 V (–). These are resistive DC ratings — inductive DC loads (relays, solenoids) need a diode or RC snubber across the load to avoid contact welding.