What type of wire may be used underground without conduit?

• A. Type UF
• B. Type THHN
• C. Type THHW
• D. Type NM-B

Answer: (A)

Direct burial-rated conductors are built to be laid in the ground without a protective conduit. UF cable, short for underground feeder, has a rugged moisture- and soil-resistant jacket that lets it be buried directly in soil under typical conditions. That makes it suitable for underground runs without conduit, though you still must follow burial depth and protection rules.

Wires like THHN and THHW are designed for use in raceways or conduits; they’re not intended to be buried directly in the ground. NM-B is designed for interior dry locations and isn’t rated for outdoor or direct burial conditions.