Most tables break down derating into two primary categories: 1. Ambient Temperature Derating

Standard ampacity ratings are usually based on an ambient temperature of 30∘C30 raised to the composed with power C 86∘F86 raised to the composed with power F

Standard tables usually assume an ambient air temperature of 30°C (86°F) or a ground temperature of 20°C (68°F). If the surrounding environment is hotter, the cable cannot carry as much current before hitting its thermal limit.