Split the underground cable into 2 circuits

Hello

The 5-core cable provides 2 circuits. I would distribute them outside onto an empty junction box. One with brown, blue, and green/yellow; the second with black, gray (blue), and green/yellow. If you take the black, brown, and gray as phase (P) and return on blue (N), the blue can quickly overheat.
Maybe you can install a sub-distribution board outside. That way you save the wiring path inside the house.

Steven

With very long cable runs, not only the voltage drop must be taken into account but also the disconnection conditions in case of a short circuit. If the fuse trips too late, there is a risk of fire. If the cable (insulation scorched, damaged) is affected, impermissible touch voltages can occur. A preceding RCD may also trip too late at these lengths. Therefore, the loop resistance must definitely be measured. Electricity makes you small and ugly.