What type of support must boxes used for wiring devices such as switches and receptacles provide?

The correct answer highlights that boxes used for wiring devices like switches and receptacles must provide substantial support. This requirement ensures that the boxes can adequately hold the weight of the devices they contain and handle the forces applied when users interact with them, for instance, plugging and unplugging equipment.

Substantial support is essential to prevent boxes from becoming loose or unstable, which can lead to malfunctioning electrical devices or even present safety hazards, such as electrical shocks or fire risks. Good installation practices dictate that these boxes should be securely housed, ensuring they remain functional and safe over time.

The other support options, while they may suggest varying levels of stability, do not meet the critical safety and performance requirements necessary for electrical installations. Minimal and temporary support could lead to inadequate stability, while sufficient support, while better, may still fall short of the robust security needed in this context. Thus, substantial support is not just preferable but necessary for maintaining system integrity and safety.