witek1646 wrote: The voltage in the sockets is 228-233V ...
Okay...
witek1646 wrote: ... although from half a year ago I remember that it was about 235-245V.
... worse, but not tragic.
witek1646 wrote: ... and as for the loop impedance, what are the standards ...?
The standard is one and Polish, but they, i.e. the local DSO, don't care ...
They are mainly and only interested in their own interest, i.e. the transmission and the associated profits and the maximum
no problems at the lowest cost, and when it comes to someone else's.

The frequent overestimation of the phase voltages gives them considerable savings. Classic conflict of interest.
Unfortunately, the stronger ... or the more annoying wins

and persistent.

:spoko:
witek1646 wrote: ... Because when I ask him, I need to know what it should be like

I don't know what to write on "What's your power supply?"

I live in the countryside
Since it's a village, you probably (like me) have an overhead line from the old days.
The impedance is better the smaller. For example, I have 0.625 ohms at 350 meters from the transformer.
And that's OK, but when it's bigger, you have bigger voltage drop (or inverter gain)
during the consumption (return) of energy.
Such a simplified Ohm's law. Exactly more complicated, because it is an alternating current
and the line capacitance comes, but more or less the point is that if some current flows, it is on the line
you have different voltage at the beginning (source) and end (receiver). While it is almost a piece of cake when collecting
because at most the old bulbs shine weaker and the engines are weaker, we have a problem the other way,
if the voltage boost by the inverter exceeds the magic 253 VAC.
Then you have something you definitely won't want to have. Problems with PV installation.
The inverter is "smart" and you obey your mom, which is the standard, and she ends (and doesn't start) at 253 volts
each phase. For me, the day started from 254-255 V which gave flowers like in the picture.

The inverter kept going into alert mode (Grid_OVP = grid voltage too high) and shut down for 3 minutes.
Then 30-60 seconds of sampling and if the voltage was (seemingly) OK, i.e.