Mains Polarity K50

What is the best mains polarity with respect to the K50 mains (IEC 14)input?

As it’s AC, can it matter? The AC get converted to DC to make things work, then it becomes important. Doesn’t the plug have a + and - on the terminals? I’m no EE though…

Yes AC (but not balanced).

At our location you have to deal with Life Neutral and PE.

Neutral and PE have approximately the same potential.
You can place the plug (SCHUKO) in 2 ways.

The leakage from Life to PE when connecting the MAINS depends on how you plug in the SCHUKO plug to the mains.

My dealer give me the answer for correct phase.