What specific characteristic defines the insulation of THWN wires?

The insulation of THWN (Thermoplastic Heat and Water-resistant Nylon-coated) wires is characterized primarily by its resistance to moisture and oil, as well as its flame resistance. This dual capability makes THWN wires particularly suitable for various applications where both environmental factors and fire safety are concerns.

Moisture resistance is crucial for ensuring that the wire can withstand exposure to water and humid conditions without degrading, helping to maintain the integrity of the electrical system. Additionally, oil resistance allows the wire to perform well in environments where it may come into contact with oil or other corrosive substances, which is essential in industrial settings.

Flame resistance further enhances safety by preventing the wire from igniting easily when exposed to high temperatures or open flames, thus reducing the risk of fire hazards in electrical installations.

The combination of moisture, oil, and flame resistance makes THWN wires versatile and reliable for many low voltage communication systems. Therefore, the specific characteristic that defines THWN wire insulation includes both its flame resistance and its moisture and oil resistance.