Good observation. We are doing this to avoid unwanted short circuit from the loads of the CCM in question. As you can see, one phase is already earthed, unintentional touching of the other phase might cause short circuit through earth. One more thing is we are using this PDM to detect the fault itself because it is sensitive to earth below 100k-ohm at energized situation. Using multimeter is not so reliable while insulation tester (megger) is not recommended for this sensitive electronic component. Keep on probing🤗!
