THHN is building wire, plastic insulated, rated 90 degrees C and 600 volts, with a nylon jacket, used in dry locations.
THHN is a common type of building wire with thermoplastic insulation and an outer nylon jacket, rated at 90 degrees C and 600 volts for use in dry locations. The letters indicate Thermoplastic, High Heat-resistant, and Nylon-jacketed, marking its heat rating and construction. The thermoplastic insulation provides the dielectric, while the tough nylon jacket adds abrasion and chemical resistance and allows the wire to pull easily through conduit.
The 90 degree C rating in dry locations makes THHN suitable for general building wiring where heat resistance is needed, and the nylon jacket improves durability and pulling. THHN is frequently produced as a dual-rated wire, also meeting THWN for wet locations, broadening its use.
In commercial and industrial construction, building wire like THHN carries branch-circuit and feeder power within conduit and raceways. Recognizing the designation helps in selecting wire matched to the location and temperature.
Because the 90 degree C rating in dry locations makes THHN suitable for general building wiring where heat resistance is needed, and the nylon jacket improves durability and pulling, it is frequently produced dual-rated, also meeting THWN for wet locations, broadening its use.
At Windy City Wire, an understanding of building wire designations, including THHN, supports clear communication about power wire. Recognizing how THHN's heat rating and nylon jacket suit it to dry-location wiring helps customers interpret references when specifying conductors for commercial and industrial construction.
THHN (Thermoplastic, High Heat-resistant, Nylon-jacketed)
NEC (National Electrical Code) and UL, which define building wire types