Wire Gauge Calculator - AWG Size & Voltage Drop | SolarRatio
Calculate the correct wire gauge (AWG) for your solar system. Enter current, wire length, and voltage to find recommended gauge and voltage drop.
Wire gauge sizing prevents voltage drop, overheating, fires, and inefficient charging in DC solar and battery circuits. The correct AWG depends on current (A), one-way run length (ft or m), system voltage, and the acceptable voltage drop percentage (typically 3% for branch circuits, 1% for charge-controller-to-battery leads). Undersized wire wastes power as heat, throttles charge current, and can trigger melted insulation or breaker failure. This tool produces a copper AWG recommendation that meets both ampacity and voltage-drop constraints under NEC 690 conduit/temperature derates. NEC 2023 Article 690 requires solar source and output circuit conductors to be rated for 1.25× the panel short-circuit current — a derating that often bumps the calculated AWG up one size from the raw voltage-drop result.
How it Works
The calculator uses Ohm's law with copper resistivity (10.4 ohm-circular-mil/ft at 20°C) to compute voltage drop: Vdrop = 2 × current × length × resistance. Round-trip length matters because current flows both ways. Compare voltage drop against system voltage to get drop percentage; if higher than the 3% target, the tool upsizes AWG one step at a time. It also cross-checks ampacity tables (NEC Table 310.16 for THWN-2 in conduit, with 1.25x continuous-load factor for solar circuits). Higher-voltage systems carry less current for the same power — a 1,000 W load at 12V draws 83 A (AWG 2 minimum), but at 48V draws only 21 A (AWG 10 sufficient). This is the dominant reason serious off-grid installations move to 48V.
Usage Scenarios
Off-grid installers run AWG 2/0 copper from a 600 Ah 48V bank to a 6,000 W inverter located 1 m away, keeping voltage drop under 1% during 125 A continuous draw. Rooftop residential PV installers size AWG 10 USE-2 between modules and combiner, then AWG 8 PV wire to the inverter with appropriate temperature and conduit derate per NEC 690 — wire sizing is typically reviewed at the AHJ permit inspection before interconnection approval. RV builders run AWG 6 between a 200 Ah LiFePO4 bank and a 2,000 W inverter, plus AWG 4 for the DC-DC alternator charger circuit. Boat builders use tinned marine cable (AWG-spec but with corrosion-resistant strands) sized one or two gauges larger to compensate for ABYC marine derating rules. Submersible pump installers calculate AWG for the entire well-head-to-pump run, often AWG 10 or 12 over 100 m for a 1 HP 240V pump.
Frequently Asked Questions
What is the maximum acceptable voltage drop for a solar system?
Keep voltage drop below 3% for efficiency. For a 12V system, that's 0.36V maximum drop. Higher voltage drop wastes energy and can cause equipment to malfunction or shut down.
Why is DC wire sizing different from AC wire sizing?
DC circuits carry current in both directions through separate positive and negative conductors, so total wire length is 2× the one-way distance. DC systems also operate at lower voltages, requiring higher current for the same power, which demands thicker wire.
What wire gauge should I use between my solar panels and charge controller?
Use the wire gauge calculator with your panel's short-circuit current (Isc) and the distance from panels to controller. Typically AWG 10–6 for runs under 30 feet at 20–40A.
Should I use copper or aluminum wire for solar systems?
Copper wire is strongly preferred for solar systems. Aluminum wire has higher resistance (requires 2 gauges thicker), is prone to oxidation at connections, and is not suitable for most solar connectors. Always use copper for DC wiring.
How do I handle wire sizing for a 48V system vs 12V?
Higher voltage systems carry less current for the same power (P=V×I), allowing thinner wire. A 1,000W load at 12V draws 83A (needs AWG 2), while at 48V it draws only 21A (AWG 10 suffices). This is a major advantage of higher voltage systems.
How to Use the Wire Gauge Calculator
Enter current (A), one-way wire length (m), system voltage (V), and maximum allowed voltage drop (%). Formula: VD = (2 × L × I × ρ) / A, where ρ = 0.0172 Ω·mm²/m for copper.
Keep voltage drop below 3% for efficiency. Higher voltage drop wastes energy and can affect device performance. Use thicker wire for long runs or high-current circuits.
DC circuits use both positive and negative conductors, so the total wire length is 2× the one-way distance. Always use the next gauge up from the calculated minimum for safety margin.