The Siemens 3RT1627-1AG21 is a capacitor contactor from the SIRIUS family, purpose-built for switching power-factor-correction capacitor banks. It is rated AC-6 at 25 kVAr / 400 V, meaning it handles the high inrush currents capacitor banks draw when they energize — standard power contactors aren't designed for that repetitive capacitive load. The coil pulls 110 V AC at 50 or 60 Hz, and the main contacts are 3 NO poles with a separate 1 NO auxiliary contact built in. This is a Size S0 frame — 45 mm wide, 100 mm tall, 135 mm deep — and it mounts on standard 35 mm DIN rail per EN 50022, either snapped on or screwed down.
The manufacturer lists this as a phased-out product. The official successor is the current SIRIUS 3RT2 series — same S0 frame size and DIN-rail footprint, but with updated coil technology and wider auxiliary options. If you have a BOM frozen around the 3RT1627-1AG21, the panel layout and wiring scheme carry over to the successor; the terminal assignments and mounting hole pattern are identical.
The AC-1 rating at 400 V is 35 A. The AC-6 rating is 25 kVAr at 400 V. The side-by-side mounting flag is Yes, so you can pack these tight on the rail without derating for heat buildup between units — useful when building a multi-step PFC bank in a compact enclosure. Terminals are screw-type on both main and control circuits. The main circuit accepts up to the standard S0 wire range.
The part carries a RoHS substance prohibition date of 01.07.2006, confirming compliance with the original RoHS directive. No specific UL or CSA listing appears in the evidence, but the SIRIUS family is typically UL/CSA recognized; verify the specific certification mark on the nameplate or request the declaration of conformity with your RFQ.