Can THHN/THWN-2 conductors be installed directly buried in the ground?

THHN/THWN-2 conductors are designed primarily for use in raceways and are not suitable for direct burial. The 'THHN' designation indicates that the insulation is thermoplastic with a nylon jacket, which is not suitable for exposure to moisture over an extended period, as it can degrade over time. Similarly, while the 'THWN' designation indicates some moisture-resistant properties, it still does not provide the necessary protections required for long-term direct burial applications.

For direct burial, conductors must have insulation rated explicitly for such purposes, like UF (Underground Feeder) cables, which are designed to withstand moisture and soil conditions. Thus, the answer indicating that THHN/THWN-2 conductors cannot be installed directly buried in the ground is correct due to their insulation limitations and the need for proper conductor types in soils.