Wire Derating |best| -

For example, a wire rated for 20 Amps at 30°C (86°F) might only be rated for 16 Amps if the ambient temperature rises to 40°C (104°F). If you are running wires through a boiler room, a hot attic, or a rooftop in direct sunlight, you must derate based on temperature.

is the practice of reducing a conductor's allowable ampacity—its maximum current-carrying capacity—to account for environmental factors that hinder heat dissipation. In electrical engineering, current flowing through a wire generates heat due to resistance; if this heat cannot escape, it can melt insulation, cause short circuits, or lead to fires.

In this setup, the wire—which is normally safe at 30A—is now only safe up to . Common Consequences of Ignoring Derating

#12 THHN, 9 conductors in conduit, ambient 45°C. Base @90°C = 30A Bundling (9 wires) = 0.70 Temp (45°C) = 0.82 Final = 30 × 0.70 × 0.82 = 17.22A

Excessive heat turns flexible insulation brittle, causing it to crack and expose live wires.