Capacitor switching contactor, S0 frame
The Siemens 3RT2628-1AC25 is a SIRIUS capacitor contactor designed specifically for switching power factor correction capacitor banks. It is built on the S0 frame, which sets its physical envelope and current-handling limits for this duty class.
Switching ratings and frequency limits
These are not motor currents — the capacitor switching duty imposes high inrush and requires the contactor to handle the surge without welding. Maximum switching frequency depends on the operating voltage: 100 operations per hour up to 480 V, dropping to 70/h at 500 V, 45/h at 600 V, and 36/h at 690 V. This limits how often the contactor can cycle the capacitor bank without overheating the arc chamber. The arcing time is specified at 10 to 10 ms, and the operating time at AC is 4 to 16 ms. These are fast enough for most power factor correction controllers that sequence capacitor steps.
Wiring and panel fit
This covers most panel wiring up to 10 mm² stranded for the main power circuit. The contactor measures 45 mm wide, 150 mm high, and 155 mm deep. The S0 frame size is a common footprint in Siemens SIRIUS contactor ranges, so panel layouts using other S0 devices can share the same DIN rail spacing.