What this contactor is and what it does
The Siemens 3RT1044-1BD40 is a SIRIUS power contactor in the Size S3 frame, designed for switching motor loads and resistive loads in industrial control panels. It mounts via screw or snap-on onto 35 mm or 75 mm standard mounting rail, so it integrates into a DIN-rail enclosure without extra bracketry. Rated at 37 kW at 500 V in AC-3 duty (standard motor switching) and 18.6 kW at 690 V, it covers the common European motor voltage bands. For heavy inrush or reversing duty, the AC-4 rating is 55 A at 400 V — that's the figure to check if the application involves plugging or jogging.
Key ratings and what they mean for fit
AC-2 rating of 30 kW at 400 V covers slip-ring motor duty where the contactor makes and breaks under load but with lower inrush than AC-4. AC-1 maximum switching frequency is 1 000 cycles per hour, which is fine for most pump and fan cycling; AC-4 maxes out at 300 cycles per hour — if the application needs faster reversing, the contactor will overheat. The 24 V DC coil draws 10 A at rated value, and the dropout time is 14 to 20 ms — fast enough for most safety circuits but not a high-speed transfer switch. Arcing time is 10 to 15 ms, so coordination with upstream fuses or breakers should account for let-through energy during that window. 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 dust or occasional condensation — no need for a conformal coating in a typical panel.
Termination and enclosure fit
Main current circuit uses screw-type terminals. Solid wire capacity is 2x (0.5 to 1.5 mm²), 2x (0.75 to 2.5 mm²), max 2x (0.75 to 4 mm²); stranded accepts 2x (10 to 50 mm²) for the power connections. The control circuit terminals take 2x (2.5 to 16 mm²) solid or stranded. Dimensions are 146 mm high, 70 mm wide, 152 mm deep — the depth is the dimension that sticks out from the DIN rail, so check panel depth clearance. The front carries IP20 protection; the terminal area is IP00, so live parts are exposed when the cover is off — standard for panel-mounted contactors.
Lifecycle and compliance
Substance prohibitance (RoHS) is declared per the date above. For UL, CSA, or other agency approvals, the nameplate and manufacturer declaration should be consulted; the evidence does not list specific marks, but SIRIUS contactors typically carry IEC and UL certifications.