Solar Wire Size Calculator — Free Online Calculator
Size wire for solar panel installations. Accounts for NEC 690 requirements including 125% continuous load factor.
How to Use This Calculator
Enter the module short-circuit current (Isc from the panel datasheet), system voltage, wire run distance, and conductor material. The calculator applies NEC 690 factors (1.25 × 1.25 = 1.5625) and limits voltage drop to 2%.
The Formula Explained
NEC 690.8 requires solar conductors be sized for 125% of Isc for continuous duty, and 690.9 requires overcurrent protection at 125% of that value, resulting in a total factor of 1.5625× Isc. Wire must also keep voltage drop under 2% for DC circuits to maintain inverter efficiency.