Can THHN conductors be used for direct burial installations?

THHN conductors are not suitable for direct burial installations primarily due to their insulation type and construction. THHN stands for "Thermoplastic High Heat-resistant Nylon-coated" wire, which is designed primarily for use in dry locations where it is protected from physical damage.

When buried directly in the ground, conductors require insulation that can withstand moisture and potential soil contaminants over time. THHN's insulation is not rated for direct exposure to moisture, which can lead to insulation breakdown and eventual conductor failure. Instead, conductors that are appropriate for direct burial installations are typically rated as UF (Underground Feeder) or similar types, designed specifically to handle such conditions.

Choosing the right conductor for a specific installation is critical to ensure both safety and compliance with electrical codes. Therefore, when planning installations that involve direct burial, it is essential to select conductors that meet the requirements for those applications to avoid safety hazards and ensure long-term reliability.