What it is and where it fits
The Siemens SIRIUS 3RT1045-1AP08-0MA0 is a size S3 power contactor in the SIRIUS family, designed for switching motor loads in industrial control panels. It mounts on 35 mm or 75 mm standard DIN rails via screw and snap-on fastening, so it integrates directly into a standard panel layout without adapters. The main current circuit uses screw-type terminals, and the front is rated IP20 with the cover or box terminal installed.
Key ratings and what they mean for fit
At AC-3 duty (standard motor switching), this contactor is rated for 37 kW at 400 V, which means it handles a typical 37 kW induction motor on a 400 V three-phase line — common for pumps, conveyors, and compressors in industrial plants. At AC-4 duty (inching or plugging), it carries 66 A at 400 V, so it supports reversing or jogging applications where the motor sees repeated start-stop cycles. The AC-1 resistive load rating is not directly stated, but the AC-3 and AC-4 figures give you the motor-duty boundaries. The contactor measures 70 mm wide, 146 mm high, and 188 mm deep, so it occupies a standard S3 footprint on the DIN rail. Side-by-side mounting is allowed, which helps when packing multiple contactors in a row without derating — useful for multi-motor control panels. Terminal capacity covers solid conductors from 0.5 mm² up to 4 mm² (in dual configurations) and stranded conductors from 10 mm² to 50 mm², so it accepts both control wiring and main power cables without adapters. The operating temperature range is -25 °C to +60 °C, and storage range is -55 °C to +80 °C, which covers most indoor industrial environments.