Thermoplastic-insulated wire is rated 600V and is designated as follows:
TW
Flame-retardant, moisture-resistant thermoplastic insulation. Rated 60°C wet or dry.
THHN
Flame-retardant and heat-resistant thermoplastic insulation with a jacket of extruded nylon. Rated 90°C dry only.
THW
Flame-retardant, moisture- and heat-resistant thermoplastic insulation. Rated 75°C wet or dry.
THW-2
Same as THW, except the wire is rated 90°C wet or dry.
THHW
Flame-retardant, moisture- and heat-resistant thermoplastic insulation. Rated 90°C dry and 75°C wet.
THWN
Flame-retardant, moisture- and heat-resistant thermoplastic insulation with a jacket of extruded nylon. Rated 75°C wet or dry.
THWN-2
Same as THWN, except the wire is rated 90°C wet or dry.
ASTM B8
Standard Specification for Concentric-Lay-Stranded Copper Conductors, Hard, Medium-Hard, or Soft
ASTM B3
Standard Specification for Soft or Annealed Copper Wire
UL 1581
Reference Standard for Electrical Wires, Cables, and Flexible Cords
UL 2556
Wire and Cable Test Methods
UL 83
Thermoplastic-Insulated Wires and Cables