Capacitor switching contactor for power factor correction banks
The Siemens 3RT1646-1AG21 is a capacitor switching contactor from the SIRIUS 3RT1 series, rated AC-6 at 50 kVAr at 400 V. This three-pole size S3 contactor uses a 110 V AC coil rated for 50/60 Hz and terminates via screw connections. The AC-6 rating means it is designed specifically for switching capacitor banks in power factor correction (PFC) panels — the inrush current from charging capacitors can exceed steady-state current by a factor of 20 to 50, and this contactor's damping resistors and contact material are selected to handle that repetitive surge without welding.
The 110 V coil draw at 50 Hz is roughly 50 VA inrush, 10 VA hold — verify the control transformer in the PFC panel has headroom for the inrush if multiple contactors pull in simultaneously. The integrated damping resistors are wired in series with the main contacts for the first few milliseconds of closure; they must be allowed to cool between switching cycles — minimum off-time per the application note is 60 seconds for full thermal recovery.