What it is and where it fits
The Siemens SIRIUS 3RT2637-1AK65 is a dedicated capacitor contactor — size S2 — built for switching power-factor-correction capacitor banks. It is not a general-purpose motor contactor; the switching characteristics are tuned for the high inrush and capacitive load of PFC stages. The coil is wound for 110 V AC at 50 Hz (120 V AC at 60 Hz) and terminates at screw-type terminals. Mounts via screw and snap-on onto a 35 mm DIN rail per DIN EN 50022, and can be rotated ±180° on a vertical surface or tilted ±22.5° forward/backward, giving panel builders flexibility in tight enclosures.
Key ratings and what they mean for your PFC bank
The headline switching capacity is 6 A at 230 V AC — that is the current it can reliably make and break for a capacitor load at line voltage. At 400 V the rating drops to 3 A, and at 690 V it is 0 A (not rated for that voltage class). These are not motor currents; capacitor switching demands higher peak current capability on closure, and this contactor is designed for that duty. Maximum switching frequency depends on the operating voltage: at 230–400 V you can cycle up to 100 operations per hour, at 480 V it drops to 50/h, at 600 V to 32/h, and at 690 V to 25/h. This matters when sizing for frequent switching applications like automatic PFC banks. Coil operating range is 0.8 to 1.1 times the rated voltage at 50 Hz — so for a 110 V coil, the pickup and hold range is roughly 88–121 V AC. Coil inrush and dropout timing is 10–18 ms AC, with an arcing time of 10–20 ms. Wire termination accepts solid conductors: 2x 0.5–1.5 mm², 2x 0.75–2.5 mm², or 2x 4 mm². For stranded wire it handles 2x 16–35 mm² or 1x 16–50 mm². At 40 °C it can take a single 50 mm² conductor; at 60 °C two 35 mm² conductors.