External electrical installation for roller shutters - how to install correctly?

Hello.
I have flush mounted roller shutters fitted. The problem is that the electrician only took out one cable for me at the corner of the window 3x1.5mm and said the blind fitters would do the rest, however the blind fitters said the electrician does it. Insulation is about to go in so I need to connect these wires myself for a quick fix.
Due to various considerations my installation at the moment looks like the picture.


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From each roller shutter comes a factory 3x0.75mm cable (stranded wire) 2.5m long and I want to connect it to a 3x1.5mm cable (wire) at the bottom. I want to connect the wires by twisting, soldering and insulating with heat shrink sleeves. All of this is to sit in a box in the polystyrene shallow under a layer of facade plaster and this polystyrene. Once connected, each 3x15 wire goes down to the garage and there I will make a switchboard in the electrical box on the wago connectors.

General question is this installation correct or am I making some glaring mistakes here ?

Specific questions:
Is the connection between the 1.5 mm wire and the 0.75 mm wire by soldering and insulating permanent or is there a chance that after years the tin will e.g. weather and the connection will crumble ?
Are there any other better and more durable types of connections?
Does the junction box for such a soldered connection, which is outside but hidden under the plaster and e.g. a centimetre layer of polystyrene foam, have to be airtight or is a simple flush-mounted junction box sufficient?
Is it permissible to run wires under the door or do the wires run above the door frame ?

Maybe alternatively, everything should be run on one 3x1.5 mm cable from the bottom, from which there is a branch line to each window in the cable junction box?
Or maybe according to the rules, such installations are made above the windows at the top and go down ?

Regards and please give some advice.

It is wrong that you are running the installation outside, that you are using boxes under the polystyrene foam and that you are doing the power supply with a 3x wire.
The power cable is five wires and the wire from the roller shutter should be fed into an up and down switch near (but not necessarily) the window.
The five-wire power supply will enable central control in the future and the switch in the room will allow you to open or close the roller shutter at any time.
This is how I would implement it.
Unless you have remote control. However, remote controls have it that very often when you need them you can't find them.

kkas12 wrote:

The power cable is five wires and the cable from the roller shutter should be fed into an up-down switch near (but not necessarily) the window.

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Presumably this is a wireless system and only the power is fed to the roller shutter cassette and the rest is taken care of by wireless buttons, wireless remote control modules, etc. which does not change the fact that the power should be run internally.

These boxes are more for aesthetic purposes to mark the place where the soldered and insulated connection is made. They could be absent as they do not have any protective function due to the fact that they are to be hidden under the styrofoam. There is already plaster inside so no installation is an option. The roller shutters are fully radio-controlled. There will be several remote controls plus smartphone control so the cables are only for power. The question is how to distribute them according to the art .

In this situation, I would not make connections under the styrofoam, to which there will be no access, but from the switchboard in the garage to each roller shutter led 3x1.5

kood wrote:

In this situation I would not make connections under the styrofoam, which will not be accessible, but from the switchboard in the garage to each roller shutter led 3x1.5

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This was the plan and the advice of one electrician but unfortunately it turned out that there are factory wires (3x0.75mm cable) coming out of the roller shutters. You can't open these roller shutters and make connections there because you lose the manufacturer's warranty. The only thing left for me to do was to somehow connect these wires outside, preferably so that I would never have to look into this connection.

All we had to do was run a pilot wire from the boxes inside the building by the windows to the outside of the walls, and that was it.
We feed the factory wires into these very boxes. You can do whatever you want with the rest of the stuff, and there are already plugs for fi 60 junction boxes on the market to imitate switches etc.

elpapiotr wrote:

From the boxes inside the building, at the windows, run a peszel with a pilot to the outside of the walls, and problem solved.
The factory wires go into those very boxes. You can do whatever you want with the rest of the stuff, and there are already plugs for fi 60 boxes on the market imitating connectors etc.

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This is actually a good idea but not in my case. I already have interior plaster and some of the cables from the roller shutters were too short to reach the cans.

The general idea was that I opened up the roller shutters by reaming out the rivets and made a normal inside cable connection through the wago and secured it with triptychs. I connected each cable from the roller shutter in the switchboard in the garage. The only visible box is where I soldered the wires, it will be hidden under the ceiling. In addition, I have run a wire from the garage circuit to the distribution board in case the soldered connection fails in a few years. Generally speaking, I may have a problem with the warranty being honoured in the event of a fault, but that remains to be seen. Nowhere does it say that the roller shutters cannot be opened. In addition, I have now learned enough about roller shutter construction to be able to repair them myself . Thanks for the hints.
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Mosqu wrote:

The only visible box is where I soldered the wires, it will be hidden under the ceiling.

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This is a good place to remember its location because you will most likely have to get to it in a few years or so.