Any Ideas for Understand one of the 3 phases has powered
If I'm interpreting your question correctly it sounds like you want to sense the presence of AC voltage at 2 points. One point is the main supply, the second point is after a switch.

You could use a resistor voltage divider to reduce the voltage to a level you could measure with a PIC, then a series diode to remove the negative half wave.
The computer I'm on right now doesn't let me run the schematic editor. I can try to add one some time later, if you need.

Keep in mind that 380V AC will KILL you if you make a mistake. If you don't have experience working with electricity PLEASE seek help from someone who does before you connect anything!