TW is the UL designation for thermoplastic-insulated wire for use in conduit, underground, and wet locations, a common building wire with a bare soft copper conductor, solid or stranded.
TW is a UL designation for a common building wire insulated with thermoplastic and rated for use in conduit, underground, and wet locations. The letters indicate Thermoplastic and Water-resistant (W), marking it as moisture-resistant building wire. It uses a bare soft copper conductor, which may be either solid or stranded, and its moisture-resistant insulation allows it to be installed where dampness or water is present.
As a moisture-resistant building wire, TW carries power circuits in the conduit and raceways of a structure, including wet and underground locations within its rating. Its thermoplastic insulation provides the dielectric, moisture resistance, and durability expected of general building wire.
In commercial and industrial construction, building wire like TW carries branch-circuit and feeder power. Recognizing the designation helps in selecting wire matched to the location and conditions.
Because it is a moisture-resistant building wire, TW carries power circuits in the conduit and raceways of a structure, including wet and underground locations within its rating, with its thermoplastic insulation providing the dielectric, moisture resistance, and durability expected of general building wire.
At Windy City Wire, an understanding of building wire designations, including TW, supports clear communication about power wire. Recognizing how TW's moisture resistance suits it to conduit, underground, and wet locations helps customers interpret references when specifying conductors for commercial and industrial construction.
TW (Thermoplastic, Water-resistant building wire)
NEC (National Electrical Code) and UL, which define building wire types