What type of insulation rating is associated with Type THHN conductors?

Type THHN conductors are rated for a maximum operating temperature of 90°C when installed in dry locations. This high temperature rating is intended for use in various applications where higher thermal resistance is necessary, such as in conduit systems or where conductors may be bundled together.

The insulation used in THHN conductors is made from a combination of nylon and thermoplastic materials that can withstand elevated temperatures. This makes them suitable for use in residential, commercial, and industrial wiring applications, especially where heat generation and ambient conditions may necessitate a higher insulation temperature rating.

Other temperature ratings listed in the options correspond to different types of insulation. For instance, conductors rated at 60°C are generally limited to older or less demanding applications, whereas 75°C conductors might be applicable in some general-purpose settings. However, the 90°C rating of THHN makes it a versatile choice for various electrical installations, particularly in environments prone to heat.