What it is and what it does
The Siemens 3RT1045-1QB44-3MA0 is a SIRIUS power contactor in size S3, designed for switching motor loads in industrial control panels. Its AC-4 rating of 66 A at 400 V means it handles severe duty cycles — plugging, inching, or reversing — where the contactor makes and breaks motor currents at full locked-rotor levels. That 66 A figure is the one that governs real-world motor reversing applications, not the higher AC-1 resistive rating.
Mounting and integration
Mounts via screw or snap-on onto 35 mm or 75 mm standard mounting rail — covers both the common DIN rail and the wider rail used in some Siemens panels. The 70 mm width and 146 mm height fit the S3 footprint; depth is 201 mm, so account for that behind the gland plate when laying out the enclosure. Side-by-side mounting is allowed, meaning you can gang contactors without a gap, but the thermal derating curve in the datasheet governs the actual current when packed tight.
Termination and wiring
Main current circuit uses screw-type terminals. Solid wire: two conductors per clamp from 0.5 mm² up to 4 mm². Stranded: two conductors from 10 mm² to 50 mm² — that's the heavy power feed. Control circuit wiring accepts solid or stranded from 0.5 mm² to 16 mm². The terminal itself is rated IP00 (unprotected), but the front of the contactor with cover or box terminal carries IP20, so finger-safe once the enclosure door is shut.
Environmental and operating limits
Operates from -25 °C to +60 °C ambient; storage range is -55 °C to +80 °C. Pollution degree 3 means it's rated for industrial environments with conductive pollution or dry non-conductive pollution that becomes conductive due to condensation — typical for most control panels not in a clean room. The coil holds at 24 V nominal with a 0.8 to 1.1 times rated voltage operating range.