What it is and what it does
The Siemens 3RT1044-3BW40 is a SIRIUS S3 power contactor — the core of motor switching and load management in industrial control panels. It's rated for a 48 V DC coil, so it pulls in clean on a standard 48 V DC control bus without a separate power supply tap. It's built for the main current circuit with screw-type terminals, which means you're landing power cables directly — no spring-cage adapters needed. The S3 frame size handles the mechanical and thermal demands of regular switching cycles.
Mounting and integration
Mounts via screw and snap-on onto both 35 mm and 75 mm standard mounting rails — that's flexibility for DIN-rail or heavy-duty backplate layouts. Side-by-side mounting is allowed, so you can pack contactors tight in a row without derating for heat buildup. IP20 on the front with the cover or box terminal in place; the terminal itself is IP00. That means the front is touch-safe for panel access, but the power lugs need clearance from grounded metal — standard practice for any screw-terminal power device. Dimensions are 146 mm high, 70 mm wide, 152 mm deep — that 152 mm depth is the key number when you're checking gland-plate clearance or enclosure depth. It's a common S3 footprint, so swapping into an existing panel layout should be straightforward if the rail and wireway are already sized for this frame.
Wiring and termination
Main circuit terminals accept solid wire 2x (0.25 to 2.5 mm²) and stranded 2x (10 to 50 mm²) — that's a wide range covering both control-signal pigtails and power conductors. The 2x notation means you can land two conductors per terminal, handy for daisy-chaining or paralleling feeds. Auxiliary or control wiring (solid or stranded) accepts 2x (2.5 to 16 mm²), which covers typical interposing relay and PLC output wiring.
Lifecycle and compliance
RoHS compliance date is 05/01/2012.