What is the insulation temperature rating of type THHN wire in a damp location?

What is the insulation temperature rating of type THHN wire in a damp location?

• A. 60°F
• B. 140°F
• C. 75°C
• D. 90°C

Answer: (D)

THHN insulation is rated for 90°C. That temperature rating applies whether the conductor is in a damp location, because THHN is designed to handle high temperatures in conduit installations, including damp environments. The other options don’t fit because 60°F isn’t a standard insulation rating, 140°F would exceed the rated capability, and 75°C is the lower rating used for some other insulation types (like THWN/THWN-2) rather than THHN.

THHN insulation is rated for 90°C. That temperature rating applies whether the conductor is in a damp location, because THHN is designed to handle high temperatures in conduit installations, including damp environments. The other options don’t fit because 60°F isn’t a standard insulation rating, 140°F would exceed the rated capability, and 75°C is the lower rating used for some other insulation types (like THWN/THWN-2) rather than THHN.