The hotel has a total of 105 rooms. Each room has 15 currents. How big is the main line required?

105 rooms, 15 currents in each room, total ***1575 currents. Because it is three-phase electricity, each item shares 525 currents equally (you should not be prepared to draw power from only one item and leave the other two items empty).

1 square meter of copper wire allows 6 currents to pass through. 525/6=87.5

But we also need to consider heat dissipation and overload issues. The wire should be thicker.