The Siemens 3RT1034-1XB40-0LA2 is a SIRUS S2 power contactor — a panel-mounted, 24 VDC-coiled switching device for motor loads up to 15 kW in AC-3 duty at 400 V, or 18.5 kW at 500 V.
The AC-3 motor rating is the one that governs real use: 15 kW at 400 V and 18.5 kW at 500 V. That means it switches a standard 4-pole induction motor up to that mechanical output under full load — not just the resistive AC-1 current. For resistive loads (AC-1), the contactor is rated for 1 200 operations per hour; for AC-3 motor switching, 1 000 ops/hour; for the heavy inrush of AC-4 reversing or inching, 250 ops/hour. Coil is 24 VDC, rated 10 A pickup at 24 V. The dropout threshold is below 18 V (0.7 × 24 V), and the DC operating time is 20 to 30 ms. Arcing time runs 10 to 15 ms — relevant for coordination with upstream fuses or breakers. Auxiliary contacts handle 6 A at 230 V, 3 A at 400 V, and 0.3 A at 220 V DC — enough for pilot duty on 24 VDC PLC inputs or small relay coils. The contactor carries a mechanical service life of 10 million operations typical. Clearance distances: 10 mm upwards, downwards, forwards, and to the side. Side-by-side mounting is permitted, which saves rail space in a dense panel.