SIRIUS Size S3 power contactor — 3RT1344-1BM40
The Siemens 3RT1344-1BM40 is a SIRIUS power contactor in the Size S3 frame, rated for motor switching up to 42 kW at 230 V at 60 °C. That 42 kW figure is the AC-3 duty rating at 60 °C ambient — the real-world motor load it can handle continuously in a warm panel. Insulation voltage is rated 1 000 V, so it's comfortable in 400 V and 690 V systems with headroom.
Main circuit terminals are screw-type, accepting stranded cable up to 2x (10... 50 mm²) or solid up to 2x (0.5... 1.5 mm²) with smaller gauges. Auxiliary and control circuits also use screw terminals. The contactor occupies 93 mm width, 146 mm height, 152 mm depth — that depth is the body plus terminals; factor it into gland-plate clearance.
Coil and switching performance
Closing power of the magnet coil at DC is 15 W. Arcing time runs 10... 15 ms, and at DC the contactor operates in 14... 20 ms. Mechanical life is typical 10 000 000 operations. At AC-1 (resistive load) it can cycle up to 1 000 1/h. For short-circuit protection with type 2 coordination, the required fuse is gL/gG 125 A.