What This Contactor Does and Where It Fits
The Siemens 3RT1045-1BG40 is a SIRIUS power contactor in the S3 frame size, designed for switching motor loads and resistive loads in control panels. It mounts on standard 35 mm or 75 mm DIN rail using the screw-and-snap-on fastening method, or can be screw-mounted directly to a backplate. The main current circuit uses screw-type terminals, which is the standard termination for panel builders who prefer secure, serviceable connections over spring-clamp. Solid wire capacity goes up to 2x (0.75... 4 mm²) maximum, and stranded accepts 2x (10... 50 mm²), so it handles the heavier power feeds typical of an S3 contactor.
Key Ratings and What They Mean for Your Load
The AC-4 rating of 66 A at 400 V is the one that matters for reversing or inching duty — the kind of starts that generate arcing on every closure. That 66 A figure tells you the contactor can handle the electrical wear of frequent plugging or jogging without welding contacts. For standard motor starting (AC-3), this contactor switches up to 45 kW at 500 V and 21.1 kW at 690 V, covering the bulk of three-phase induction motors in the 30-60 hp range depending on line voltage. The AC-2 rating of 37 kW at 400 V covers slip-ring motor duty where the rotor circuit is switched. Mechanical life is typical at 10 million operations, and the AC-3 switching rate maxes at 1,000 cycles per hour — fast enough for most conveyor or pump cycling, but not for high-speed pick-and-place. The AC-4 rate drops to 300 cycles per hour, reflecting the heavier arc wear in that duty.
Environmental Fit and Protection
Operating temperature range is -25 to +60 °C, which covers most indoor panel environments. Storage range is broader at -55 to +80 °C, so it survives shipping and warehouse extremes. The front of the contactor carries IP20 protection with the cover or box terminal fitted — enough for a closed panel, but not for washdown areas. Pollution degree 3 means it's rated for industrial environments with conductive dust or occasional condensation, typical for non-sealed control cabinets in factories.
Lifecycle and Sourcing Reality
RoHS compliance is documented with a substance prohibition date of May 1, 2012, so it meets the EU directive for lead and other restricted substances. No special compliance documentation beyond the standard declaration is needed for most industrial installations.
Panel Integration Notes
Dimensions are 70 mm wide, 146 mm high, and 152 mm deep — a compact S3 footprint that fits alongside other SIRIUS components on the same DIN rail. Side-by-side mounting is permitted, so you can gang multiple contactors without spacing, which saves rail space in dense panels. The auxiliary contact block options (not included with this base unit) share the same coil suppression as the main contactor. If you're adding aux contacts downstream, verify free-wheel diode polarity before energizing inductive loads — standard practice for any DC-suppressed coil circuit.