What this SIRIUS capacitor contactor is and where it lands
The Siemens 3RT2645-1AB05 is a SIRIUS capacitor contactor — Size S3 — purpose-built for switching capacitor banks in power factor correction (PFC) duty. Unlike a standard motor contactor, it handles the inrush surge a discharged capacitor presents when it hits the line. The coil pulls 24 V AC at 50 Hz, and the screw-type terminals on the magnet coil mean you can land field wiring without special tooling. It mounts via screw or snap-on onto 35 mm DIN rail per DIN EN 50022, so it drops into a standard panel enclosure with no adapter plate.
Key ratings — what they mean for your circuit
Rated 6 A at 230 V AC and 3 A at 400 V AC, this contactor is sized for the capacitor currents you'll see on a 50 Hz line. At 690 V AC the rating drops to 0 A — it's not intended for 690 V capacitor switching. The DC switching ratings (6 A at 24 V, 2 A at 60 V, 1 A at 110 V, 0.9 A at 125 V, 0.3 A at 220 V) cover control-circuit or small resistive DC loads, not the capacitor bank itself. The arcing time runs 10 to 20 ms, and the switching rate tops out at 200 operations per hour at 230 V — that's fine for daily PFC cycling but not for a rapid-pulse application. Operating temperature spans -25 to +60 °C, storage -55 to +80 °C, so it lives comfortably in a warm panel room or a cold warehouse.
Terminal capacity and wiring
The power terminals accept solid wire up to 2x 4 mm² or stranded up to 2x 70 mm² (1x 70 mm²). At 40 °C ambient you can land a single 50 mm²; at 60 °C derate to 2x 35 mm². The auxiliary contact block (attachable, one slot) uses smaller terminals: 2x 0.5 to 1.5 mm² solid, 2x 0.75 to 2.5 mm² stranded. That covers most control-circuit wiring without needing a reducer. The 80 mm width and 140 mm height fit a standard S3 footprint on the DIN rail.