Does it make sense to have a three-phase installation in an apartment connected to one phase?

I live in a prefabricated building. There are 5 adults living there. We are planning to renovate the electrical installation. The plan was to switch to a three-phase installation due to the multitude of electrical devices and the connection power of only 5 kW. The existing aluminum installation now requires agreement on who has the right to use what and when, so that it does not trip the fuse, which is very inconvenient. Unfortunately, the housing cooperative stated that it was not possible to install a three-phase system because the vertical line would not support it. Maybe they will modernize it someday, but we don't know when...

In this situation, during renovation, can I install a three-phase installation inside the apartment for 3 x 6 = 18 kW (with the future in mind), which will now temporarily operate on one phase? In other words, I want to be able to do everything needed for three phases, and when the administration replaces the risers, I can only run the cable to the apartment from the meter and not change anything else in the apartment. Temporarily, however, it would have to operate in one phase. The question concerns everything: cables, electrical sockets, fuse board.

You can do anything in your apartment, of course you can prepare a 3F installation, but write to the power company in your area about the power allocation.

OK, so as I understand it, I can have a universal installation in my apartment that will work with both 1 and 3 phases, depending on what I connect to it.

As for the power allocation, the cooperative told me that they could agree to increase the allocation to 8 kW on the existing cables, but they stipulated that "the plant will definitely not agree." I was told on the plant's hotline that if the cooperative agreed, they had nothing to say because it was not their responsibility. Who really makes decisions on these issues?

Trójfaza wrote:

OK, so as I understand it, I can have a universal installation in my apartment that will work with both 1 and 3 phases, depending on what I connect to it.

As for the power allocation, the cooperative told me that they could agree to increase the allocation to 8 KW on the existing cables, but they stipulated that "the plant will definitely not agree". I was told on the plant's hotline that if the cooperative agreed, they had nothing to say because it was not their responsibility. Who really makes decisions on these issues?

You can, or more precisely, an electrician can perform the installation in apartment 1f prepared for apartment 3f. After changing the power supply, unfortunately, you will need to visit an electrician to connect the wires in your switchgear a little differently.
If the cooperative agrees and ZE can increase the power on one phase, it is definitely a good solution.
As for me, I would rather have 1F with a higher amperage connected to my apartment than 3F with lower amperage.
When it comes to decision-making, both SM and ZE must agree.
Just remember that a 5x2.5 cable at 3f is required to connect induction. At 1f it will be at least 3x4. If you decide to install 1f with higher power with the option to switch to 3f, you must use a 5x4 cable.

Trójfaza wrote:

OK, so as I understand it, I can have a universal installation in my apartment that will work with both 1 and 3 phases, depending on what I connect to it.

In an apartment, the difference between a 1f and a 3f installation basically comes down to the fact that in a 3f installation there is one 3f circuit (for a possible electric stove) and the rest are 1f, but powered from different phases.
And of course, you can commission this installation so that the 1f-3f switchover occurs automatically.
In my opinion, however, this solution involves unnecessary costs.
The solution proposed by @ktoś_tam is the most optimal.
And I would suggest using a 5x4mm² cable to power the electric kitchen, and additionally make a separate circuit for the oven.

Trójfaza wrote:

In this situation, during renovation, can I install a three-phase installation inside the apartment for 3 x 6 = 18 KW (with the future in mind), which will now temporarily operate on one phase?

Even you should!
All the more so because a modern home (apartment, too) installation is (or should be) practically indistinguishable from the switchgear whether it is single-phase or three-phase. Only the connections in the switchboard determine this.

Thanks for your answers! I submitted an application to the cooperative to increase the power to 8 KW in one phase. If I receive consent, I will go to the operator. When submitting the application, they told me that if I insisted on three phases, they would agree if I ran the line from the main switchboard at my own expense, and that would be 5 ceilings and about 25 m of cable. I think I'll hold off...

In connection with a similar topic, I have a theoretical question, namely whether it makes sense to install 3f in such a case? (Apart from the hob in the kitchen). What I'm aiming for is that I want to separate some rooms in the house as a separate apartment. If I assume correctly 25A for 2.5mm², the output for 3f is over 9kW. But now when I start dividing the phases into rooms, for example the kitchen separately, the boiler separately, the rest separately, the 9kW is not so obvious anymore. If I have a load of 16A on each of the divided parts of the apartments at one moment, then I have 48A on the N wire of the connection, right? Do I understand that correctly? So at least 4mm² or even better 6mm² on the connection from the main fuses to the planned new part of the apartment?
Thanks in advance.

andrew.musiol wrote:

I have a theoretical question

Starting point for the discussion.

andrew.musiol wrote:

If I assume correctly 25A for 2.5mm², the output for 3f is over 9kW

Clearer, please, my Lord What is 25A, what is 2.5mm². What do you think these 9 kW are?
I will leave the rest of your post without comment because it is simply fiction.

andrew.musiol wrote:

In connection with a similar topic, I have a theoretical question, namely whether it makes sense to install 3f in such a case? (Apart from the hob in the kitchen). What I'm aiming for is that I want to separate some rooms in the house as a separate apartment. If I assume correctly 25A for 2.5mm², the output for 3f is over 9kW. But now when I start dividing the phases into rooms, for example the kitchen separately, the boiler separately, the rest separately, the 9kW is not so obvious anymore. If I have a load of 16A on each of the divided parts of the apartments at one moment, then I have 48A on the N wire of the connection, right? Do I understand that correctly? So at least 4mm² or even better 6mm² on the connection from the main fuses to the planned new part of the apartment?
Thanks in advance

If I understood correctly, the load current under the cable cross-section for a power of 9000W÷230V = 39.13A and this is if there is no voltage drop, which is unlikely.
A single-phase meter can be loaded with a maximum load (the information on the plate is, e.g., 5/40A for induction, 60A for electronics), so it will withstand the load. However, the WLZ in the staircase certainly does not have such a cross-section, unless in the ZK at the BMs. The administration or cooperative is responsible for the installations in the staircase and they give approval for the connection.

To the author, these 8kW are probably with a load on three phases because the cooperative agreed to this power. There are places where the heating of an apartment in a block of flats is connected in a ZK cabinet on 4x10mm² BMs and goes to the 4th floor and is protected against the B40A meter. So the event is expensive.

andrew.musiol wrote:

Does it make sense to install 3f in such a case?

In what case?
Please explain your problem precisely, my friend, because what you wrote is completely incomprehensible