Continuous load must not exceed 80% of the derated ampacity (or conversely, the derated ampacity must be ≥ 125% of the continuous load).
NEC Table 310.15(B)(2)(a) for 45°C ambient, 90°C insulation = 0.87 55A × 0.87 = 47.85A derating wire
Introduction: The Silent Killer of Electrical Systems Every year, fires, motor failures, and power supply meltdowns trace their root cause to a single, overlooked design step: failing to derate a wire. Continuous load must not exceed 80% of the
Table 310.15(C)(1): 7–9 conductors = 70% 47.85A × 0.70 = 33.5A derating wire
Required ampacity = 45A continuous × 1.25 = 56.25A