Capacitor switching contactor, AC-6 rated, 25 kVAr at 400 V
The Siemens 3RT1627-1AN21 is a capacitor contactor from the SIRIUS family, designed specifically for switching capacitor banks in power factor correction (PFC) applications. Its AC-6 duty rating of 25 kVAr at 400 V means it handles the high inrush currents typical of capacitor charging without welding the main contacts — a standard contactor would fail prematurely here. The coil is 220 V AC, 50/60 Hz, and the contactor provides 3 normally open main contacts plus 1 normally open auxiliary contact, all terminated with screw-type terminals.
This part is a phased-out product. The manufacturer lists the successor as the SIRIUS 3RT2 series — the same S0 frame size and similar electrical ratings, so a panel swap should be straightforward.
The S0 footprint is 45 mm wide, 100 mm tall, and 135 mm deep — that depth is a bit more than the standard S0 contactor (typically ~91 mm) because of the integrated surge-suppression network for capacitor switching. Side-by-side mounting is allowed with no spacing, so you can pack several units on a rail for multi-step PFC banks. Front protection is IP20; the terminals are IP00, meaning the wiring area is not finger-safe — keep the panel door closed or add terminal shrouds.
What the AC-6 rating means for your PFC bank
The AC-6 duty class is specific to capacitor switching. The 25 kVAr at 400 V rating corresponds to a capacitor current of about 36 A, but the contactor must handle the peak inrush — up to 100 times the rated current for a few milliseconds. The 3RT1627-1AN21 is built with damping resistors and a dedicated switching sequence to limit that surge. If you are replacing a failed unit, verify the capacitor bank size does not exceed 25 kVAr per step; for larger banks, step up to the next SIRIUS frame size.