Thermal Derating

Category: science

The mechanical reduction of allowable current inside conductors passing through high ambient heat zones.

Distinct from wire grouping derating, thermal derating explicitly factors in environmental conditions—such as a rooftop conduit exposed to blazing direct sunlight. Ambient roof temperatures can soar far past standard air readings, requiring wire adjustments to prevent insulation failure.

Common Examples

• We applied a strict thermal derating multiplier to our commercial rooftop solar line calculations to account for the extreme 120°F deck heat.
• Failing to track thermal derating limits across unconditioned attic runs violates long-term building safety and inspection covenants.