nixdorf:
Let's say that I have 3x230v outputs and all I want Arduino to do is to "check" if there is a 230v or not 230v.
In that case all you need is an opto isolator. Have a resistor, diode and capacitor in series to turn on the LED inside the opto isolator, then use the output to feed into a digital input.
If there is to light up an LED or not.
Do you want the arduino to do anything else because if not you don't need one.