What type of cable is needed from the fuse box to the stove connection?

My father had a house built in 1975. For the first 15 years, there was a normal electric stove installed. After that, my parents had a gas stove for 30 years. Now the gas stove has given up its life, and an electric stove should be installed again. The connection socket is still there. I bought an electric stove as well as a stove connection cable 5 x 2.5 qmm. A good, very technically skilled friend who has connected many things already installed the stove yesterday. Now he has slept on it and comes with the following remark: He has thought about the supply line from the fuses in the hallway to the kitchen. There, a cable thickness of 2.5 mm2 should be used. But at most 1.5 mm2 is available. Now I am supposed to ask an electrician whether this is okay or if the supply line to the kitchen would have to be renewed. Otherwise, overload and fire hazard. My father is 83 and will "freak out" if now all the walls have to be broken open.

The house is from 1975, so not that old after all. Would all the walls now have to be broken open to lay a new line from the fuse box to the stove?

I live in a house built in 1962. There, an electrician connected an electric stove to the existing line in 1995, and that was definitely the original line. Everything has worked perfectly until today.

How long is the cable from the distributor to the connection box?
How is the cable secured in the distributor?
What kind of stove/cooktop is now connected and how (3-phase, 2-phase, ...)?

How long is the cable from the distribution box to the connection socket? How is the cable secured in the distribution box? What kind of stove/cooktop is now connected and how (3-phase, 2-phase, ...)?

It is 3 to 4 meters from the fuse box to the stove connection socket. In the fuse box, there are 3 toggle switches responsible for the stove connection. New regular electric stove with oven and ceramic cooktop. 3-phase - as I understood it.

For the short distance, that should not be a problem.

However, if you or you all have so little knowledge that you talk about toggle switches instead of B-16A, etc. circuit breakers and also cannot name the power consumption of the oven, you definitely should not tinker with the electrical system yourselves!

Without guarantee:
Probably nothing will happen given the length. I probably wouldn't sleep very peacefully though, especially since the 83-year-old dad might sometimes forget the stove and it could be on for more than just 1 hour. Of course, it's all just theory...

The change in cross-section is borderline. Since there was already an electric stove connected here earlier, I would take another look at the cross-section from the sub-distribution to see if there really is 2.5 mm² inside.

Your acquaintance should also reflect and check whether he actually connected the stove three-phase.
Single-phase with 5x1.5 would be beyond borderline ;).

EDIT: In what type of wall is the 5x1.5² located (brick, drywall with insulation wool, etc.)?

No guarantee: Probably nothing will happen given the length. I probably wouldn’t sleep completely easy, especially since the 83-year-old dad might also forget the stove on and it would stay on for longer than just 1 hour. Of course, this is all just theory... The change of the cross-section is borderline. But since there was an electric stove connected here before, I would check the cross-section from the sub-distribution again to see if it’s really 2.5 mm². Your acquaintance should also take a moment to reflect and check whether he really connected the stove three-phase. Single-phase with 5x1.5 would be beyond borderline ;). EDIT: In what type of wall is the 5x1.5² cable located (brick, drywall with insulation wool, etc.)?

Well, my father doesn’t use the stove anymore anyway. At most, his good acquaintance might warm something up or cook potatoes, but it will never be on for longer than 1 hour at a time and never more than 2 plates simultaneously. They probably won’t even use the oven... The cables are in brick walls, so interior walls. There is no wood or insulation in there...