The 3RT1627-1AC21 is a phased-out product. The official Siemens successor is the SIRIUS 3RT2627-1AC25.
The AC-6 rating of 25 kVAr at 400 V is the critical spec: it defines the maximum capacitor bank size this contactor can switch without excessive inrush current or contact wear. The 24 V AC coil (50/60 Hz) draws its control voltage from a standard control transformer; the 3-pole main contacts handle the three-phase capacitor circuit. A single NO auxiliary contact (1 NO) is integrated for status feedback or interlocking.
At 45 mm wide, 100 mm tall, and 135 mm deep, it occupies the standard S0 footprint. Side-by-side mounting is permitted with zero spacing, saving panel width.
The part carries a RoHS compliance date of 01.07.2006, indicating it meets the original RoHS directive.