PV Conductor Ampacity Calculator

Smallest copper size that passes both ampacity tests for a PV string, combiner output or inverter AC circuit.

Design aid, not a substitute for the adopted code, the equipment manual or your AHJ. Copper, 90°C-rated wire, ampacities as printed by Southwire and LugsDirect (Table 310.16, 2020 and 2023 values agree for these sizes), ambient and adjustment factors as printed by Elliott Electric (2020 NEC). It does not check voltage drop, conduit fill area, the overcurrent device or the equipment grounding conductor.
Examples:

Method. Step 1: maximum circuit current is Isc × 1.25 for each string, multiplied by the number of parallel strings; for AC it is the inverter's continuous output current. Test 1: the terminal-column ampacity (no derating) must be at least 125% of that current. Test 2: the 90°C ampacity × ambient factor × adjustment factor must be at least that current. The size must pass both. Whole-degree bands: a fractional temperature moves to the next band up. Sizes 3 AWG and 1 AWG are skipped because only one source printed them. 60°C column values come from LugsDirect (2020) and agree with the two sizes IAEI (2011) prints.