Wire Gauge Calculator

Voltage drop is the loss of electrical pressure as current flows through wire. In solar systems, excessive voltage drop wastes energy as heat and can prevent charge controllers and inverters from operating correctly.

NEC guidelines recommend: maximum 3% voltage drop for branch circuits, and 5% total for feeder + branch combined. For low-voltage DC systems (12V and 24V), keeping drop under 3% is critical since every volt matters.

The calculator uses round-trip distance (wire runs to the load and back) and NEC Table 310.16 ampacity ratings at 75°C. It applies a 125% continuous load safety factor per NEC 210.20 when sizing both wire and breakers.

Pro tip: If voltage drop is too high, consider increasing your system voltage (e.g., 24V or 48V instead of 12V) before upsizing wire. Doubling voltage cuts current in half, which reduces voltage drop by 75%.

For full AWG reference tables and NEC ampacity ratings, see our solar wire gauge chart. If you're wiring panels and need help choosing between series and parallel configurations, our panel wiring guide explains how each configuration affects current and wire sizing.