Yes, it's possible to detect electrical activity in an AC power cable noninvasively using Qvar functionality as described in ST's AN5755. The Qvar sensor can sense electrostatic charge variations when electrodes are placed near the cable's outer insulation. The electrodes, typically made of conductive material, should be placed close but not touching the cable.
For the input circuitry, high impedance (megaohms range) is required to prevent signal interference, along with filtering to eliminate noise, focusing on the AC signal's frequency (50/60 Hz)
