So I'm working on a project using a Curiosity Nano board for development. The Curiosity board sits on a custom PCB which has a mains voltage resistance divider to read the mains voltage, and a few outputs, along with its own capacitive power supply with full-wave rectification (similar to ones used in energy meters; not isolated from mains). The final product will be powered entirely by this supply, and I plan to power the AVR on the curiosity from this supply as well instead of from the USB port on it. However, I'd also like the on-board nEDBG connected to my computer for programming and debugging during testing, which would mean that the USB ground gets connected to the ground of the mains capacitive power supply. I'm afraid this might put my rather expensive computer at risk if something goes wrong, which I'd like to avoid. Am I correct in thinking this? What are my options here?