In which scenarios are non-metallic boxes prohibited?

Non-metallic boxes are specifically prohibited in high-temperature areas or where physical damage is likely due to their material properties. Non-metallic boxes are made from plastic, which can warp or degrade under high temperatures, compromising the integrity and safety of electrical systems. Additionally, in environments where physical damage is possible—such as in industrial settings or areas with significant foot traffic—non-metallic boxes may not provide the necessary protection for wiring and connections, as they are not as durable as their metallic counterparts.

Using non-metallic boxes in these conditions could lead to safety hazards, including electrical failures or fires, which is why the Code sets these clear limitations to ensure installations not only comply with the NEC but are also safe and reliable in various environments.

The other scenarios mentioned, such as low moisture areas, outdoor installations, or low voltage applications, do not inherently pose the same level of risk for non-metallic boxes. In fact, non-metallic boxes are often suitable and frequently used in low moisture and low voltage applications, as well as in certain outdoor installations, depending on specific conditions and ratings.