Capacitor Switching on a 24 VDC Coil — S0 Frame
The Siemens 3RT2628-1BB45 is a SIRIUS capacitor contactor, purpose-built for switching capacitive loads in power factor correction banks. Its 24 VDC coil (screw-type terminals) pulls in with a 0.8 x rated voltage pickup threshold and releases with dropout below 18 V — a clean, predictable magnet curve for PLC-driven control circuits. Rated for capacitor switching at 230 V (6 A), 400 V (3 A), and 690 V (1 A), the contactor's S0 frame (45 x 150 x 165 mm) fits standard 35 mm DIN rail per EN 50022, with screw and snap-on fastening. Switching frequency tops out at 100 operations per hour at 230/240/400 V, dropping to 36 ops/h at 690 V — the arc time of 10 ms and DC switching time of 15–18 ms define the thermal recovery window. For repetitive capacitor bank cycling, stay under these limits to avoid contact welding.
The 24 VDC coil is the control side — it draws from a 24 VDC power supply, not an AC control transformer. The 0.8 x rated pickup means the coil will reliably pull in at 19.2 V, giving margin against a sagging bus. The 1.1 x full-scale value is the maximum continuous overvoltage the coil can tolerate without damage — important if your 24 VDC bus runs high. Capacitor switching currents are given per voltage: 6 A at 230 V, 3 A at 400 V, 1 A at 690 V (–). These are not the same as a general-purpose contactor's AC-1 or AC-3 ratings — capacitor contactors must handle inrush currents up to 100× the rated capacitor current without welding. The S0 frame's contact geometry is designed for that high-peak stress. Wire termination: solid conductors accept 2x (0.5–1.5 mm²), 2x (0.75–2.5 mm²), or 2x 4 mm². Stranded conductors accept 2x (1–2.5 mm²) or 2x (2.5–10 mm²). The screw terminals are rated for 1x 16 mm² at 40 °C and 1x 25 mm² at 60 °C — the higher temperature rating reflects the lower current density at the terminal for larger wire.
Panel Integration and Environmental Limits
The S0 frame occupies 45 mm of rail width — standard for a contactor of this class. No auxiliary contact block is attached from the factory (— 0 attachable). If you need auxiliary contacts for status feedback or interlocking, the contactor accepts SIRIUS side-mount or top-mount auxiliary blocks — order them separately.