The Siemens 3RT2637-1AV03 is a capacitor contactor from the SIRIUS series, rated AC-6b 75 kVAr at 400 V for switching capacitive loads. The 3-pole configuration with a 400 V AC 50 Hz coil and screw terminals fits standard panel layouts. Size S2 frame keeps the DIN-rail footprint compact for power-factor correction banks.
What the AC-6b rating means for fit
AC-6b is the IEC utilization category for switching capacitor banks. The 75 kVAr at 400 V rating governs the maximum reactive power this contactor can make and break without welding or excessive wear. That figure assumes a 50 Hz supply; the inrush current from discharged capacitors is typically 20–30× rated current, so the contactor's design margin in AC-6b is what protects the bank and the panel. A standard AC-3 motor-rated contactor of similar frame size would not survive repeated capacitor switching.
Screw terminals accept 1.5–6 mm² stranded or solid copper. The 400 V AC coil draws its rated VA at pickup and lower holding VA — verify the control transformer is sized for the inrush if multiple contactors pull in simultaneously. The auxiliary contacts are electrically isolated from the main poles, so feedback wiring to a PLC input is straightforward.