Abstract: A flush-mounting electrical box assembly has preassembled electrical control elements contained therein. The box assembly may be flush mounted in unfinished walls to protect the electrical control elements during wall finishing works. The assembly comprises a box, a frame and an outer protective cover. The box has an open side and one or more removable zones or portions to provide openings for the passage of the cable ends or terminals of the electrical system or installation and relative flexible protecting tubes. The frame accommodates and secures at at least one electrical control element (such as a switch, socket or the like) and elements for securing the frame to the edge surrounding the open side of the box. The frame is of an outer size and shape to be completely received in the box with at least one electrical control element applied and connected to the system or installation terminals. The outer protection cover or lid is removably mounted to the open side of the box.