What it is and what it does
The Siemens 3RT2636-1AV05 is a capacitor contactor — a three-pole switching device purpose-built for switching power-factor correction capacitor banks. Its AC-6b rating of 50 kVAr at 400 V AC, 50 Hz means it handles the high inrush current and transient load that capacitors present when energised, without welding contacts or degrading prematurely. That 50 kVAr figure is the one that governs fit for your bank size — not a generic motor rating. The coil is 400 V AC, 50 Hz, and the contactor carries 2 NC auxiliary contacts wired via screw terminals. The S2 frame size is a standard Siemens footprint that mates with the usual DIN-rail mount and busbar system in a panel. If you're swapping one into an existing capacitor bank cabinet, the mechanical interlock and auxiliary wiring pattern are the same as other S2 contactors in this family.