Hello I am trying to measure 240v mains AC as safely as possible. There seems to be 2 ways to do it, which of the two is better and preferred?

1. Voltage divider directly from the mains

I have found an schematic that seems to be form a data sheet of an adc where in the mains is directly voltage divided and connected to the adc

[![enter image description here][1]][1]

Rhi is 300k Ohm and Rlo is 750 ohm . I dont know why the 3 300kOhm are in series though. I do not know how to pick a appropriate varistor though i assume a 375 peak to peak voltage , would [this][2] be correct? Also is that earth or ground (adc ground) where neutral is connected because they sometime interchange the two and it becomes confusing in these situations.

2. Voltage divider After a transformer

This approach seems to be the safer one but not a space saving one using a very small transformer like [this][3] that can output 5v and voltage divide from that

[![enter image description here][4]][4]

Is the ground necessary? I only added it because the other circuit added one.

My Thoughts

The reason i like number one is because it can be made much more compact than the second, I cannot decide if is it worth the protection of the entire circuit for a compact size. How likely is circuit 1 more to fail than circuit 2? [1]: https://i.sstatic.net/Qj6ig.png [2]: https://www.digikey.com/product-detail/en/tdk-electronics-inc/B72660M0461K093/495-76488-1-ND/7669897 [3]: https://www.digikey.com/product-detail/en/hammond-manufacturing/160D10/HM4117-ND/455009 [4]: https://i.sstatic.net/75SjH.png

Hello I am trying to measure 240v mains AC as safely as possible. There seems to be 2 ways to do it, which of the two is better and preferred?

1. Voltage divider directly from the mains

I have found an schematic that seems to be form a data sheet of an adc where in the mains is directly voltage divided and connected to the adc

Rhi is 300k Ohm and Rlo is 750 ohm . I dont know why the 3 300kOhm are in series though. I do not know how to pick a appropriate varistor though i assume a 375 peak to peak voltage , would this be correct? Also is that earth or ground (adc ground) where neutral is connected because they sometime interchange the two and it becomes confusing in these situations.

2. Voltage divider After a transformer

This approach seems to be the safer one but not a space saving one using a very small transformer like this that can output 5v and voltage divide from that

Is the ground necessary? I only added it because the other circuit added one.

My Thoughts

The reason i like number one is because it can be made much more compact than the second, I cannot decide if is it worth the protection of the entire circuit for a compact size. How likely is circuit 1 more to fail than circuit 2?