OpenEnergyMonitor Community

Current monitoring circuit for Arduino

I’m considering using the current monitoring circuit at here
Looking into the Arduino connections and the provided code, things kind of make sense. But I don’t understand what C1 is for. It mentions diverting the AC current, but why is that needed? I searched here, and have been Googling it, but no clear explanations yet. Any thoughts on what it’s for? Thanks.

It is providing a low impedance path to the common for a.c. current, in effect, it is anchoring the mid-point so that it is an a.c. ground. Without it, the impedance of the midpoint (given the resistor values shown: 5 kΩ - 235 kΩ) would be in series with the input signal, and that would attenuate it so giving invalid readings.