What it is and what it does
The Siemens 3RT1044-1AL20-ZW95 is a SIRIUS power contactor, size S3, designed for switching motor loads in industrial control panels. It carries a rated power of 37 kW at 500 V AC-3 duty, and 18.6 kW at 690 V — the AC-3 rating is the one that governs motor switching, not the AC-1 resistive figure. That means for a 37 kW, 500 V motor on a conveyor or pump, this contactor handles the inrush and breaking without welding contacts.
Mounting and integration
Mounts via screw or snap-on onto 35 mm and 75 mm standard DIN rails — the snap-on feature speeds panel assembly, and the 70 mm width plus 146 mm height fits the S3 footprint common in Siemens SIRIUS motor starter combinations. Side-by-side mounting is supported, so you can gang multiple contactors on the same rail without extra spacing.
Termination and wiring
Main current circuit uses screw-type terminals. Solid wire accepts 2x (0.5 to 1.5 mm²), 2x (0.75 to 2.5 mm²), and up to 2x (0.75 to 4 mm²). Stranded wire takes 2x (10 to 50 mm²) for the larger power feeds. That range covers most motor branch circuits from fractional kW up to the 37 kW rating — the 50 mm² stranded capacity is enough for the full load current without needing a terminal adapter.
Environmental and protection
IP20 on the front with cover or box terminal; the terminal itself is IP00, so it expects enclosure protection in the panel. Operating temperature range is -25 to +60 °C, storage from -55 to +80 °C. Pollution degree 3 means it's rated for industrial environments with conductive pollution — typical for a control panel without climate control.