The Siemens 3RT1034-1AC20-1AA0 is a SIRIUS S2 power contactor — the core switching device for motor loads in a control panel. It's rated 15 kW at 400 V in AC-2 duty (slip-ring motors, reversing starts), 18.5 kW at 500 V, and 10 kW at 690 V, so it covers the common European motor voltages up to that power band. The coil is 24 V 50/60 Hz, which is the standard control voltage across most industrial panels. The S2 frame size is the mid-range in the SIRIUS contactor family; it's a fast mover for general motor switching up to about 7.5 kW direct-on-line or 15 kW in AC-2 duty. Conductor cross-section range is generous: solid up to 2x 4 mm², stranded up to 2x 25 mm², so it handles the wire sizes you'd expect for this current class without needing lug adapters.
The 15 kW at 400 V AC-2 rating is the one that decides the motor size it can handle in reversing or inching applications — AC-2 is harder on contacts than AC-3 because the motor is re-energized against a rotating field. If your load is a standard squirrel-cage motor (AC-3), this contactor will switch a higher kW than the AC-2 figure; the AC-3 rating isn't listed here, but the S2 frame typically covers up to 18.5 kW at 400 V AC-3. For resistive loads (AC-1), the switching frequency can go up to 1200 operations per hour; for AC-4 (plugging/reversing at full load), it drops to 250 per hour — that's the contact wear limit. The auxiliary contacts handle 10 A at 24 V, 6 A at 230 V, 3 A at 400 V — enough for a PLC input or a small relay coil. IP20 on the front, IP00 at the terminals: the terminals are live when the panel door is open, so standard finger-safe terminal shrouds are expected.
The dimensions are 112 mm high, 55 mm wide, 115 mm deep — that's the S2 envelope, which is about the size of a small relay base plus a bit of depth for the arc chamber. The 24 V coil holds in at 0.8 to 1.1 times rated voltage at 50 Hz (0.85 to 1.1 at 60 Hz), so it stays pulled in even if the control transformer sags a bit.
For a maintenance planner: this is a fast mover in the SIRIUS line. Keep one on the shelf if you have multiple panels with S2 contactors — the 24 V coil variant is the most common control voltage, so it covers the majority of swap-outs. The screw terminals mean no special tooling needed for replacement; a standard screwdriver is all it takes.