THHN wire is rated for 90°C, but is typically used at 75°C for the following reasons: National Electrical Code (NEC): The NEC requires that THHN wire be used at 75°C or less in wet or damp locations. This is because the insulation on THHN wire can deteriorate at higher temperatures in the presence of moisture. Safety Margin: Using THHN wire at 75°C provides a safety margin to account for potential temperature fluctuations and overloads. Operating the wire at a lower temperature reduces the risk of insulation failure and electrical fires. Longer Wire Life: Running THHN wire at a lower temperature extends its life expectancy. Insulation degradation is accelerated at higher temperatures, so operating the wire at 75°C can help to extend its service life. Compatibility with Other Components: Many electrical components, such as circuit breakers and switches, are designed for use with THHN wire rated at 75°C. Using THHN wire at a higher temperature could damage these components.Therefore, while THHN wire is rated for 90°C, it is generally used at 75°C to comply with safety codes, provide a safety margin, extend wire life, and ensure compatibility with other electrical components. Flag for review