After the installation is complete, cover the notch with a metal shield, available in the electrical section of home stores. Repair the wall over the shield and the hole in the ceiling to finish.
Anything that will allow electricity to pass through it is a conductor. Metals are typically good conductors with copper being one of the best.
Also called an old-work box, these are electrical boxes with built-in clamps to fasten them into finished walls. All that is needed to install one is to cut a hole the proper size in the hollow part of a wall and insert the box. These can be used in drywall, plaster or paneling. They are best suited for adding wall receptacles and switches. Because they don’t offer much support, old work boxes are not a good choice for installing a new ceiling fixture.
At the floor the wallboard is cut to allow for boring a hole in the soleplate. Then the run can be made from an upper floor to the room below or vice versa.