The question with just such a title was asked by the reader Roman.
This is already 41 questions from the "question-answer" series.
I quote verbatim the text of the question posed by Roman:
380V 20 kW comes to the house, a 380V 15 kW boiler is installed. Is it possible to connect all other consumers to one of the phases if the old wiring does not allow the load to be divided into phases.
I reviewed the issue and advised Roman within the framework of my knowledge and qualifications as follows:
You can use any scheme for connecting household electrical appliances, including those with asymmetrical phase loading - this is your choice. Yes, it is desirable to redistribute the connected equipment evenly between phases. However, if your home electrical circuits do not allow you to power at least rooms with separate phase conductors, then you will have to proceed from the available parameters.
The option you proposed will significantly reduce the reliability of the "system" - since in the absence of voltage in one of the phase conductors, the rest would provide power supply to at least part of the premises. Otherwise, they will simply remain unused.
I also have a question about the suitability of the old electrical wiring to work with such a load. Is the cross-section of the conductors enough to connect the load, at least the same 5 kW, which will remain after the deduction of the heating boiler?
Perhaps the electrical wiring is already so worn out that it is time to replace it? Then, in the process of designing and installing new electrical wiring in the house, you can independently ensure the connection of all three phases, and the problem will be solved.
P.S. Link to some of the past Q&A parts - Part 40, Part 39, Part 38, Part 37, Part 36.