Which of the following items is classified as a system or package?

The correct answer is identified as a system or package because a cable tray serves a specific function in the electrical distribution system. It is designed to support and manage multiple electrical cables, allowing for organized routing and protection, making it integral to a planned electrical infrastructure.

A cable tray often forms part of an overall system that includes various components working together to ensure safe and efficient electrical distribution. This concept encompasses both functional and structural aspects, categorizing it as a package due to its capability to accommodate a comprehensive solution for cable management.

In contrast, the other options represent individual components or materials rather than systems. For example, #12 AWG THHN is a specific type of wire; 4-square boxes are mounting boxes for electrical devices; and receptacles are the outlets where electrical devices connect. Each of these items serves a distinct purpose in the electrical installation but does not collectively function as a system on its own.