Which type of box must be used for outdoor installations to protect against moisture?

The correct choice for outdoor installations to protect against moisture is weatherproof boxes. These boxes are specifically designed to provide a high level of protection against moisture and environmental conditions that can occur outside. Weatherproof boxes typically feature sealed covers and may be made from materials that resist corrosion and degradation when exposed to the elements.

In outdoor electrical installations, ensuring that the junction boxes are adequately sealed is crucial for preventing moisture from entering, which could cause short circuits, corrosion, or failure of electrical components. Using weatherproof boxes complies with safety standards set by the National Electrical Code (NEC), thereby ensuring both safety and the longevity of the installation.

Standard plastic boxes are not suitable for outdoor use unless they are specifically labeled as weatherproof. Metal boxes do not inherently provide moisture protection unless they have the same weatherproof ratings as specified. Unlisted boxes do not meet the necessary safety standards and therefore should not be used in outdoor applications, as they may not be designed to withstand moisture or environmental factors.