Capacitor switching contactor, AC-6b rated
The Siemens 3RT2637-1NB33 is a 3-pole capacitor contactor rated for AC-6b duty at 75 kVAr at 400 V. That AC-6b category is the IEC designation for switching capacitor banks — the contactor is designed to handle the high inrush current and repetitive switching of power-factor correction capacitors without welding or excessive wear. The coil accepts 20-33 V AC/DC, 50/60 Hz, with an integrated varistor for surge suppression across the coil terminals.
Built-in varistor and auxiliary contacts
An integrated varistor clamps voltage transients from the coil, which is standard practice for capacitor switching where the coil sees frequent energization. The auxiliary contact block provides 1 NO + 1 NC, wired via screw terminals. Size S2 frame means it occupies a defined DIN-rail footprint consistent with the SIRIUS 3RT2 family — panel layout stays predictable if you're replacing or expanding an existing bank.