The Siemens 3RT2637-1AL23 is a SIRIUS capacitor contactor, size S2, designed for switching capacitor banks in power-factor correction panels.
Switching capacity varies by voltage: at 230 V it handles 6 A, at 400 V it handles 3 A, and at 690 V it is rated 0 A — meaning this contactor is not intended for 690 V capacitor switching. The arcing time is 10–20 ms, and the maximum switching frequency at 230–400 V is 100 operations per hour, dropping to 25 per hour at 690 V. These limits govern the duty cycle for repetitive capacitor switching; exceeding them shortens contact life. Terminals accept solid conductors from 0.5 mm² up to 4 mm² (2x) on the control side, and stranded conductors up to 50 mm² on the power side — sized for the capacitor inrush current typical of PFC banks.