What does the letter H in Type THWN insulation represent?

The letter H in Type THWN insulation specifically designates that the insulation is heat resistant. This classification is essential for understanding the thermal performance of the wire used in electrical applications. THWN stands for Thermoplastic Heat and Water-resistant Nylon-coated, where the "H" signifies that the insulation can withstand high temperatures, making it suitable for environments where heat may be a concern. This capability to resist heat is crucial for maintaining the integrity and safety of electrical installations, especially in scenarios where wires may be exposed to elevated temperatures.

Understanding the properties represented by the letters in wire insulation types helps in selecting the appropriate wiring for specific applications, ensuring both compliance with safety standards and optimal performance in various conditions.