THHN Wire vs. THWN wire
THHN stands for Thermoplastic High Heat-Resistant Nylon coated. It is the most popular wire for use in construction but can also be used to wire control circuits, machine tools and certain electrical appliances.
THWN stands for Thermoplastic Heat and Water resistant Nylon coated. Water resistance is the major reason for its use. The stand alone cables are not coated in vinyl but rather in PVC for water resistance. They are used in areas where a conduit is not a must.
Both THHN and THWN are available in solid or stranded conductors depending on the size and are manufactured in aluminum or copper and covered in polyvinyl chloride (PVC) insulation with a nylon jacket. They are commonly alternating current electrical distribution systems at voltage levels of between 110 and 600 volts.