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Wire size calculation of PV system

Question asked by on Oct 15, 2018
Latest reply on Oct 25, 2018 by charlespicard32

Recently a solar PV systems sales outfit sent me a drawing for a 1500w PV system, comprised of 2 parallel strings of 3 250w  panels in series going to a combiner box. Each string developed 105v at just under 7.4a each, for a total combined amperage of 14.7a. Section 690.8 states that the sum of the amperage of all modules in parallel times 125% be used to calculate the conductor size. 14.7  X 1.25 = 18.375a. To be safe I would use #10 THHN in the conduit to carry the current the 50 ft to the charge controller. The sales outfit claims that each collector is a module at 7.4a, and all 6 taken in parallel develope roughly 44a. 44a X 125% = 55a which requires #6 wire to the charge controller. In this case, what does section 690.8 require, #10 or #6 to the controller? Remember that the actual output of the array, as wired is 14.7a. Isn't that the value times 125% used to calculate the wire size?