What it is and what it does
The Siemens SIRIUS 3RT1034-1AL20-1AA0 is a Size S2 power contactor designed for switching motor loads in industrial control panels. It's rated for 18.5 kW at 500 V in AC-3 duty, which covers the majority of three-phase squirrel-cage motor applications — pumps, fans, conveyors — where the contacts make under load but break only after the motor is up to speed. The contactor mounts on a 35 mm DIN rail per EN 50022, using either screw-clamp or snap-on fastening. Its 55 mm width and 112 mm height fit standard panel layouts; side-by-side mounting is supported without derating, which matters when you're packing multiple contactors into a row.
Key ratings and what they mean for fit
The AC-3 motor rating of 18.5 kW at 500 V is the headline number for this size — it tells you the contactor can handle a 25 A motor at 500 V under normal starting duty. For 400 V networks, the AC-2 rating is 15 kW, which applies to slip-ring motors or loads with longer starting times. At 690 V the contactor is rated for 10 kW, so it's not a universal high-voltage machine; match the voltage to your line. Auxiliary contact ratings are given for several control voltages: 10 A at 24 V, 2 A at 60 V, 1 A at 110 V, 0.3 A at 220 V, 6 A at 230 V, and 3 A at 400 V. These are the make/break capacities for the auxiliary circuit — if you're feeding a PLC input or a relay coil, stay within these limits at the applied voltage. The contactor is rated for Pollution Degree 3, meaning it's suitable for industrial environments where conductive pollution or dry non-conductive pollution that becomes conductive due to condensation can occur. The front face carries IP20 protection; the terminals are IP00, so they require enclosure protection in the panel. Operating temperature range is -25 to +60 °C, storage from -55 to +80 °C. That covers most indoor panel environments, including unheated warehouses.
Wiring and connection details
Main circuit terminals are screw-type. Solid wire: 2x (0.5 to 1.5 mm²), 2x (0.75 to 2.5 mm²), max 2x (0.75 to 4 mm²). Stranded: 2x (0.75 to 25 mm²). Mechanical life is rated at 10 million operations typical, which is standard for a contactor of this class. Switching frequency limits vary by duty: 1200 cycles/hour for AC-1 (resistive), 1000 for AC-3 (motor start/run), 750 for AC-2, and 250 for AC-4 (plugging or inching). If your application requires frequent jogging, the AC-4 limit is the one to watch.