Which containers must be used for supporting single-conductor PV wires in outdoor locations?

The correct choice addresses the requirements set forth by the National Electrical Code (NEC) for supporting single-conductor photovoltaic (PV) wires in outdoor locations. Cable trays are specifically designed to support multiple conductors, including single-conductor PV wires, while providing sufficient ventilation and protection against environmental factors such as moisture, UV rays, and physical damage.

Using cable trays ensures that the wires are organized and secured properly, which helps in maintaining compliance with safety standards. The design of cable trays also accommodates changes in direction and elevation of wires without needing significant modifications, thereby simplifying installation.

In contrast, while other containers like PVC piping, metal conduit, and plywood boxes might serve different purposes in electrical installations, they do not fulfill the same criteria as cable trays for outdoor photovoltaic applications. For instance, PVC piping and metal conduit are generally used for protecting conductors but do not offer the necessary support for multiple wires in a non-encapsulated manner, and plywood boxes lack the durability and weather resistance needed for outdoor installations. Therefore, the use of cable trays aligns best with NEC guidelines for supporting outdoor PV installations effectively.