Run electricity from the house to the garage

I am burying a 400v underground cable.

Whatever that is supposed to mean.

The cross-section of the cable will have to be calculated.

Underground cable, min. 5 cores, cross-section adapted to power requirements. If you use the existing connection, the cross-sections of this supply line must also meet your power requirements. The power connection should also be designed for the power, if necessary you need a different or additional connection. A clean solution is to lay directly from the fuse box with a conduit (HT).

If you have the electrician connect the cable directly in the box and into a socket in the garage, then he can certainly advise you on the cross-section for another 10 minutes beforehand and you will have a clean solution.

Nyy 5x10, the CAD 7 cable is also available as an underground cable. Be sure to include the warning tape as a cautionary sign. Naturally buried frost-free in the ground.

I'll jump in here because I have the same issue. I want to install a wallbox in the garage and the existing 3x1.5mm² cable is not suitable for that. So I will lay a new cable in 5x6mm² (cross-section chosen with some reserve). The cable has to go through the masonry cellar wall. The house is a renovated old building from 1956. There are no existing empty conduits. The insulation extends 50cm into the ground. Below that is just the wall. In that area I want to go frost-proof. Are there more elegant solutions than simply drilling a hole of the appropriate size and sealing it again with construction foam and silicone? The soil outside is sand and the cellar is absolutely dry. We don’t have waterlogging. Therefore, watertightness is relatively uncritical. Retrofitting a multi-utility entry seems a bit overkill for one power and one Ethernet cable.

Thanks for all the hints,
Michael

There are also single-division introductions ;-)
Still significantly priced.

O-ring, approx. €100 each. Not a bargain, but clean, simple, and permanently trouble-free.