PV Circuit Maximum Current and Ampacity (NEC 690.8, the 156% Rule)
Sizes the PV source/output-circuit maximum current = module Isc x paralleled strings x 125% (690.8(A)(1)) and the minimum conductor ampacity = that maximum x another 125% (690.8(B)(1)), the two factors stacking to 156% of Isc, before any conditions-of-use derate. The conductor must also satisfy 690.8(B)(2) and the greater governs; the engineer governs.
Formula and source
max_current = Isc x strings x 1.25 (690.8(A)(1)); min_ampacity = max_current x 1.25 (690.8(B)(1)); the factors stack to 1.5625 (156%) of Isc, before conditions-of-use derate; also size for 690.8(B)(2) and take the greater.
PV source/output-circuit current and conductor ampacity, NEC 2023 690.8(A) and 690.8(B), by name.
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