Which type of floor boxes must be used for receptacles located in the floor?

The correct choice emphasizes that floor boxes used for receptacles installed in the floor must be "listed" to ensure they meet safety and performance standards set forth by the National Electrical Code (NEC). A listed floor box is recognized by an authoritative organization that tests and evaluates products according to specific safety criteria and performance standards.

Using listed floor boxes is crucial because they are designed to safely house electrical connections while protecting them from environmental factors such as moisture and damage from foot traffic. These boxes are constructed to handle the unique load and application conditions present in floor installations, which include protecting wiring and ensuring safe access to electrical circuits.

In contrast, standard, generic, or universal floor boxes may not meet the established requirements for electrical safety and installation standards mandated by the NEC. Such types may lack the necessary certifications and could potentially lead to safety hazards if installed. Therefore, selecting a listed floor box is essential for compliance with the NEC and to maintain a safe electrical installation in residential or commercial settings.