Is it safe (for the equipment) to power Raspberry Pi with 5V offset 240VAC inputs

[SakerCobalt]

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.

 

[Bluejets]

Just use transformer isolation and be safe.
Non-isolated supplies are definetely not for the open wiring environment nor the amatuer.

 

[SakerCobalt]

I decided to just measure 120V and connect all the ground together with the earth ground of the line I am measuring. Still wondering if the above would work or if it would cause unanticipated problems. Looking at my setup, everything on the pi/arduino side is electrically isolated, so as long as it isn't touched, would it work?

 

[Harald Kapp]

I decided to just measure 120V and connect all the ground together with the earth ground of the line I am measuring.

A bad decision. You thereby created direct connection between the normally safe 5 V side and mains. This can be lethally dangerous.

Looking at my setup, everything on the pi/arduino side is electrically isolated, so as long as it isn't touched, would it work?

It will work, but it is definitely unsafe. I repeat: don't do it. The power supply is isolated for a good reason. don't break that isolation barrier.
Use a transformer as suggested by @Bluejets .

If you insist on not using a transformer, we can't keep you from doing so. In that case I urge you to make the connection in the following way:

Calculate R_burden such that measured voltage /mains = Rburden / (Rburden + 300 kΩ). Use 1/4 W leaded resistors, place them physically in series in a layout as shown in the schematic. Use higher values like 475 kΩ if possible (will depend on R_burden and the voltage divider ratio you can accept). The higher the ratio the better.
You gain a little bit of safety with this arrangement because current will be limited by the series resistors in each leg. Also, should one resistor develop a short circuit, the other resistors will still offer some limited protection by limiting the current.
BUT: In any case this is still a direct connection to mains and is possibly dangerous. I definitely do not recommend to use it. I repeat: use a transformer. A few coins well invested in your safety.
Or use an isolation amplifier - but I guess that is too expensive if you don't even want to afford the small cost of a transformer.