What this contactor is and what it does
The Siemens 3RT1034-3AN20 is a SIRIUS power contactor — Size S2, screw-type terminals for the main circuit, designed for switching motor loads in industrial control panels. It carries an AC-3 rating of 18.5 kW at 500 V, meaning it handles the inrush and run currents of a standard three-phase induction motor at that voltage without derating. The AC-2 rating at 400 V is 15 kW, covering slip-ring motor or soft-start applications where the contactor makes and breaks under load. Mounting is screw and snap-on onto 35 mm DIN rail per DIN EN 50022 — the same rail as every other SIRIUS component in the panel, so it integrates without adapter plates. The 55 mm width and 115 mm depth fit standard enclosure backplates; side-by-side mounting is permitted, so you can gang multiple contactors on the same rail segment without derating for heat buildup.
Key ratings and what they mean for fit
The headline motor rating is 18.5 kW at 500 V AC-3 — that is the duty cycle for starting and disconnecting a squirrel-cage motor under full load. At 690 V the same contactor is rated for 10 kW, which reflects the higher voltage stress on the arc chamber. The AC-4 rating (plugging/reversing) is 250 switching cycles per hour, compared to 1 000 per hour for AC-3 — if your application involves frequent inching or reversing, the AC-4 limit governs service life. Operating temperature range is -25 to +60 °C, with storage from -55 to +80 °C. The IP20 front enclosure means the contactor is touch-safe when mounted in a closed panel; the terminal area is IP00, so it requires the panel's own protection against accidental contact. Pollution degree 3 suits industrial environments with conductive dust or occasional condensation.
Sourcing and lifecycle reality
If you are managing a multi-year category plan, the SIRIUS platform is Siemens' core industrial contactor family with broad cross-series compatibility — the same accessories, same DIN-rail footprint, and same auxiliary contact blocks across S2 frame sizes. That reduces second-source qualification risk if you ever need to substitute within the family.
Terminal wiring and conductor sizing
The main circuit accepts screw-type terminals: solid conductors 2x (0.25 to 2.5 mm²) and stranded conductors 2x (0.75 to 25 mm²). The wider stranded range covers the full cross-section for a 18.5 kW motor circuit at 500 V — typically 6 to 10 mm² depending on cable length and installation method. The auxiliary/control terminals accept 2x (0.75 to 16 mm²) stranded, which is generous for control wiring.