Rooftop Conduit Sunlight Ambient Adder (NEC 310.15(B)(2))
Applies the NEC 310.15(B)(2) rooftop sunlight adder, 33 C (60 F) where a raceway is less than 7/8 in above the roof, to a measured ambient and then the 90 C-column temperature correction (a #8 at 55 A in a 95 F ambient on the roof -> 155 F design ambient -> ~0.58 -> ~32 A). Raising the raceway onto standoffs at or above 7/8 in removes the adder and recovers most of the ampacity. The AHJ-adopted edition governs.
Formula and source
adder = 60 F (33 C) where height above roof < 7/8 in (0.875 in), else 0; design_ambient = measured + adder; corrected = base_ampacity x (90 C-column correction factor at the design ambient).
Raceways and cables exposed to sunlight on or above rooftops, NEC 2020/2023 310.15(B)(2), with the 310.15(B)(1) 90 C-column ambient correction, by name.
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