What it is and what it does
The Siemens 3RT1035-1BW40 is a SIRIUS power contactor in the S2 frame size, designed for switching motor loads and resistive loads in industrial control panels. The 48 VDC coil pulls in with a typical arcing time of 10 to 15 ms and a DC dropout delay of 20 to 25 ms — fast enough for most sequencing but worth noting if your safety circuit needs a defined off-delay. Rated for AC-3 motor switching at 400 V, it delivers 18.5 kW, and at 500 V it handles 22 kW. The AC-4 rating at 400 V is 35 A, which covers reversing or inching duty where the contactor breaks full-load current. Mechanical life is typical 10 million operations.
Mounting and wiring
Mounts via screw and snap-on onto 35 mm DIN rail per EN 50022. Side-by-side mounting is allowed, so you can gang multiple contactors without a gap — useful when panel space is tight. The S2 footprint is 55 mm wide, 112 mm tall, 130 mm deep. Main circuit terminals are screw-type, accepting stranded wire up to 2x 25 mm² or solid up to 2x 4 mm². The minimum permissible conductor at 40 °C is 16 mm² — that's the thermal limit, not a wiring convenience. Pollution degree 3 means it's rated for industrial environments with conductive contamination.