What this contactor is and where it fits
The Siemens 3RT1044-1AL20-ZX95 is a SIRIUS power contactor in frame size S3, designed for switching three-phase motor loads in industrial control panels. It carries a 230 V 50 Hz / 230 V 60 Hz coil and uses screw-type terminals for the main current circuit. The contactor is rated for 37 kW at 500 V and 18.6 kW at 690 V in AC-3 duty, which is the standard category for squirrel-cage motor starting — that rating tells you the maximum motor load it can switch under full load without accelerated contact wear.
Mounting and integration
Mounts via screw or snap-on onto 35 mm or 75 mm standard DIN rails. Side-by-side mounting is permitted, which saves panel width when grouping multiple contactors. The S3 frame occupies 70 mm width, 146 mm height, and 139 mm depth — check your gland plate clearance before committing the layout.
Terminal capacity and wiring
Screw-type terminals on the main current circuit accept solid conductors from 2x (0.5... 1.5 mm²) up to max 2x (0.75... 4 mm²), and stranded conductors from 2x (10... 50 mm²). The auxiliary circuit accepts 2x (2.5... 16 mm²) solid or stranded. That range covers most motor branch circuit wiring up to the 37 kW rating — no need for terminal adaptors unless you're landing aluminum conductors.
Environmental and protection ratings
Front of the contactor carries IP20 protection — safe against finger contact with live parts inside the enclosure. The terminal area itself is rated IP00, meaning it relies on the panel enclosure for touch protection. Rated for pollution degree 3, which covers conductive pollution or dry non-conductive pollution that becomes conductive due to condensation — typical for industrial control rooms without climate control. Operating temperature range is -25 to +60 °C, storage from -55 to +80 °C.
Switching performance and life
Mechanical life is 10 million operations typical. Maximum switching rates vary by duty: 1000 cycles per hour in AC-1 (resistive) and AC-3 (motor start/run), 400 in AC-2 (slip-ring motor), and 300 in AC-4 (plugging/inching). The arcing time is 10 to 15 ms, and the operate time at AC is 10 to 19 ms. These numbers matter for coordination with upstream protection — the contactor clears fast enough that a downstream short won't weld the main contacts if the breaker opens within a few cycles.