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.
Hold the outlet box against the ceiling about midway between the joists and trace the outline with a pencil. Cut a channel from one joist to the other, the same width as the outlet box. Use a drywall saw to cut gypsum board and a reciprocating saw to cut wood lath plaster.
Apply caulk to the back of the strip and stick it to each stud. Press it down until it’s flush with the wall surface. You can leave the wallboard off, but it’s best to put it back in place. Caulk along the seam to seal out air drafts and then reinstall the baseboard.
If the existing receptacle or switch is connected through the holes in the back, push a jewelers screwdriver or similarly shaped tool into the slot next to each hole to release the clamp pressure and pull the wire free.