Which of the following classifications pertains to an electrical installation that is built into the structure?

The classification that pertains to an electrical installation built into the structure is concealed wiring. This type of wiring is integrated within walls, ceilings, or floors, meaning it is not visible and is protected from physical damage. Concealed wiring is typically used to maintain the aesthetics of a space and ensure that the wiring is safe from accidental contact or interference.

In contrast, surface wiring refers to installations mounted on the surface of walls or ceilings, making them visible. Exposed wiring is also visible and is often used in certain applications where accessibility is necessary. Temporary wiring is installed for a limited duration, commonly seen in construction sites or special events, and is not intended as a permanent solution. The key difference for concealed wiring lies in its integration into the building structure, providing a safe, efficient, and visually appealing electrical system.