Which type of conductor is appropriate for direct burial underground feeder circuits?

The appropriate conductor for direct burial underground feeder circuits is Type UF (Underground Feeder) cable. Type UF cable is specifically designed for underground use and is rated for direct burial, making it resistant to moisture and suitable for installation without additional protection, such as conduit. It has a durable, moisture-resistant jacket that protects the conductors from environmental factors and physical damage, making it a preferred choice for applications ranging from outdoor outlets to lighting.

In terms of the other options: Type XHHW is typically used for wet or dry locations in conduit and is not designed for direct burial without additional protection. Type TW is primarily used in dry locations and is not suitable for harsh environments. Type USE (Underground Service Entrance) is also a viable option for some underground applications but is not as commonly used for feeder circuits as UF. Therefore, UF cable is the best choice for direct burial underground feeder circuits due to its specific construction and rating for this purpose.