The Siemens 3RT2037-1KB44 is a SIRIUS coupling contactor — a Size S2 unit with a 24 VDC coil, screw-type terminals, and a footprint of 55 mm wide by 114 mm tall by 174 mm deep.
Coil and switching behaviour
The coil is rated 24 VDC with a holding current draw of 6 A at rated voltage, and an inrush peak of 2.6 A. Dropout delay on DC is 30 to 55 ms, and arcing time runs 10 to 20 ms — useful to know when coordinating control logic timing or suppression networks. The coil connection uses screw-type terminals accepting 2x (0.5 to 1.5 mm²) or 2x (0.75 to 2.5 mm²) solid or stranded wire.
Switching capacity and duty ratings
This contactor carries main contacts rated 18 to 1 (likely a NO/NC configuration count per the SIRIUS convention). Switching frequency varies by duty class: up to 800 operations per hour at AC-1 (resistive), 700/h at AC-3 and AC-3e (motor starting/running), 400/h at AC-2 (slip-ring motor), and 200/h at AC-4 (plugging/inching). For DC switching, the ratings are voltage-dependent: 6 A at 24 V, 2 A at 48 V and 60 V, 1 A at 110 V, 0.9 A at 125 V, 0.3 A at 220 V, 3 A at 400 V, and 0.6 A at 440 V. At 230 V AC it is rated for 10 hp motor load.