Conductors operating at higher ambient temperatures require a correction factor from NEC Table 310. The correction factor reduces the usable ampacity of a conductor in proportion to how far the operating environment exceeds 30°C. Properly sizing PV conductors and their associated Overcurrent Protection Devices (OCPDs) is a foundational skill for any electrician in the solar industry, governed by the solar panel wiring code found in NEC Article 690. Correct calculations are not just for performance; they are a critical. The section covers how to calculate maximum circuit current, how to set minimum conductor ampacity, and what correction factors apply before you land on a wire gauge. Solar conductor sizing under 690. The factors in the table are applicable. For XLPE cable at 45°C ambient: k_temp = √ [ (90−45)÷ (90−30)] = √ [45÷60] = 0. Grouping / Bundling Derating Factor (k_group): When n cables are installed in mutual contact (bundled in tray, conduit, or duct), the mutual thermal heating effect reduces each cable's effective ampacity.
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