Outdoors. THHN wires are suitable for both indoor and outdoor use. The THHN wires are also installed in conduits without the need for additional protection. The conduits are usually installed underground which offer sufficient protection for the THHN wires.Click to see full answer. In this manner, can Thhn wire be used in outdoor conduit?THHN is still the single conductor wire used outdoors and in conduit because the THWN rating can resist water, oil, gases and solvents. However, running 3-4 single wires can be difficult for the installer because they’ll have to run each one individually or tie all 3 together and try to run them as one. where can Thhn wire be used? THHN wires are used for damp and dry locations only. When you need wiring for a wet location, the THWN wire is more suitable. It is important to know than today many of the wires on the markets are dual-rated for both the THWN and THHN, this means both types of wires can be utilized in wet, dry and damp locations. Consequently, what kind of wire do you use for outdoor conduit? Type UF cable is the most commonly used nonmetallic cable for residential outdoor wiring runs. UF cable can be direct-buried (without conduit) with a minimum of 24 inches of earth cover.Is Thhn wire waterproof?Thermoplastic, high heat, Nylon coated. THHN wire without a dual approval of THWN is not water resistant. The added “W” stands for water resistant so that it could be installed outdoors and in conduit when THHN wire could not. However, again, remember that they’re all combined into a universal wire now.