I have a project where I am using 240VAC (1phase) to supply a Mean Well IRM-01-5 AC to DC converter which then supplies an Arduino and Raspberry Pi ZeroW.
I want to measure the voltage across the lines, so I am only planning to use the 2 line voltages so I can power the AC to DC converter and supply the voltage to be sampled. My sampling is a voltage divider across the 2 AC lines arbitrarily designating one of them as ground.
The IRM-01-5 appears to isolate the input from output, so I am thinking about connecting the DC ground to one of the input lines which will make a common DC ground bus. I am thinking that will be ok on the power supply, and my DC bus will give me 5V, but it will be riding on a 240VAC waveform.
I probably won't do this, but I am unsure what potential issues this could cause other than shocking anyone that touched the raspberry pi while this setup is running.