THW is building wire, plastic insulated, heat, flame, and moisture resistant, rated 75 degrees C.
THW is a building wire with thermoplastic insulation that is heat, flame, and moisture resistant, rated at 75 degrees C. The letters indicate Thermoplastic, Heat-resistant, and Water-resistant (W), marking its suitability for both wet and dry locations. The moisture-resistant thermoplastic insulation allows THW to be used where dampness or water may be present, broadening its application compared with dry-only building wire.
The 75 degree C rating and moisture resistance make THW a versatile general building wire for power circuits in a range of locations. Its flame resistance contributes to the fire performance expected of building wire in a structure.
In commercial and industrial construction, building wire like THW carries branch-circuit and feeder power in conduit and raceways, including wet locations. Recognizing the designation helps in selecting wire matched to the location and temperature.
Because the 75 degree C rating and moisture resistance make THW a versatile general building wire for power circuits in a range of locations, its flame resistance contributes to the fire performance expected of building wire in a structure, suiting it to wet and dry installations.
At Windy City Wire, an understanding of building wire designations, including THW, supports clear communication about power wire. Recognizing how THW's moisture resistance and heat rating suit it to wet and dry locations helps customers interpret references when specifying conductors for commercial and industrial construction.
THW (Thermoplastic, Heat- and Water-resistant)
NEC (National Electrical Code) and UL, which define building wire types