Which of the following insulation types is NOT moisture resistant?

The correct answer is that THHN insulation is not moisture resistant. THHN (Thermoplastic High Heat-resistant Nylon-coated) is primarily designed for use in dry and wet locations, but it is not rated specifically for moisture resistance like other types. The nylon coating provides some degree of protection and allows it to function well in dry environments, but it is not as robust against moisture as other insulation types.

In contrast, THW (Thermoplastic Heat and Water-resistant), THWN (Thermoplastic Heat and Water-resistant Nylon-coated), and THHW (Thermoplastic Heat and Water-sensitive) are specifically designed to have moisture-resistant properties, making them suitable for use in wet locations. These types of insulation can handle exposure to moisture and are commonly used in applications where water exposure is likely.

Understanding the characteristics of different insulation types is essential for ensuring that the wiring is suitable for its intended environment, helping to prevent failures and enhance safety in electrical installations.