The Siemens 3RT2637-1AF03 is a SIRIUS capacitor contactor, size S2, designed specifically for switching power-factor-correction capacitor banks. The contactor is rated for switching capacitor currents at various voltages: 6 A at 230 V, 3 A at 400 V, and 0 A at 690 V — meaning it's sized for low-voltage capacitor banks up to 400 V line-to-line. The arcing time is 10 to 20 ms, and the switching frequency at 230 V and 400 V is up to 100 operations per hour, dropping to 25 per hour at 690 V.
Dimensions are 65 mm wide, 114 mm high, 130 mm deep (S2 frame). Terminals accept solid conductors: 2x (0.5 to 1.5 mm²), 2x (0.75 to 2.5 mm²), or 2x 4 mm². Stranded: 2x (10 to 35 mm²) or 1x (10 to 50 mm²). At 40 °C the terminal can take 1x 50 mm²; at 60 °C, 2x 35 mm². An attachable auxiliary switch block (1 instantaneous contact) is available for feedback or status indication.