Electric stove connection from one phase to three

Why do you need a machine in the "zero" and even more so in the "earth"? To connect a three-phase consumer, in your case electric stoves, use a five-core cable with the same cross-section of conductors. 3 phases are connected to a three-pole AB. You need to do this.

It is impossible that the zero cross section be 2.5 mm², and the phases 6 mm², because it is not known what current will be in it. You can look at connecting the heating elements in an electric stove and count, but you need to know their power. Indeed, heating elements in an electric stove, in fact, are connected even in a three-phase connection as single-phase consumers, they simply connect differently, by star. And the neutral wire current will be equal to the current consumption of the heating element, if 1 heating element is turned on, if the heating elements are turned on in all three phases, then the neutral wire current will be equal to the difference in the load of each phase. The heater of each burner can consume different power, this is the whole problem.