THWN and THHN are both insulation grades for wires used in building wiring. Both types of wire are made of copper conductors for excellent conductivity, with a thermoplastic insulation that provides durability and flexibility, and this insulation helps the wire resist heat and physical damage. And both have an outer nylon jacket, the nylon coating adds an extra layer of protection against abrasion, chemicals, and moisture. Typically, both THHN and THWN wires are rated for 600 volts, which are suitable for use in conduit or raceway for most standard electrical applications in residential, commercial, and industrial settings.
What is the difference between THWN and THHN?
THWN wire has the same thermoplastic coating as THHN, but is also water resistant. The "W" in the THWN stands for water resistance. THWN is suitable for wet or dry environments. It can withstand temperatures up to 75°C (167°F) in wet environments and up to 90°C (194°F) in dry environments. THHN is suitable for dry environments only. THHN can withstand higher temperatures (90°C) in dry environments. THWN is typically used where the wire may be exposed to moisture, such as outdoor or underground installations, while THHN is typically used indoors in dry environments.