THHN (Thermoplastic High Heat-resistant Nylon-coated) wire is designed with a PVC (polyvinyl chloride) insulated nylon sheath. Most THHN building wire comes with the dual rating THHN/THWN, meaning it is usable in both wet and dry conditions, as well as both indoor and outdoor use.
THHN carries a UL rating of 90 degrees Celsius in dry environments and 75 degrees Celsius in wet environments. The conductor can either be copper or aluminum and either stranded or solid. It is available in 12 colors and is generally used in electrical applications of 600V or less.
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