Solar Cable Sizing Guide: Which AWG Wire Do You Need?
- Undersized cable is a fire hazard — always size for the maximum current the fuse allows, not just your expected load.
- Two factors determine cable size: ampacity (how much current it can carry) and voltage drop (how much power you lose over distance).
- Keep voltage drop under 3% for DC runs. Use the calculator below to check your runs.
- Battery-to-inverter cables are the most critical — they carry the highest current in the system.
- Use tinned copper marine-grade wire for outdoor and engine bay installations.
AWG ampacity reference table
Ampacity is the maximum current a cable can carry continuously without overheating. Always size cable to handle the fuse protecting that circuit — not just your expected current.
| AWG size | Max amps (chassis) | Max amps (bundled) | Common use |
|---|---|---|---|
| 18 AWG | 16A | 10A | Small signal wires, sensor runs |
| 16 AWG | 22A | 13A | Lights, small 12V accessories |
| 14 AWG | 32A | 17A | Panel to controller (small systems) |
| 12 AWG | 41A | 23A | Panel strings, controller to battery (small) |
| 10 AWG | 55A | 33A | Controller to battery (medium systems) |
| 8 AWG | 73A | 46A | Battery to inverter (small inverters) |
| 6 AWG | 95A | 60A | Battery to inverter (1,000–2,000W) |
| 4 AWG | 125A | 80A | Battery to inverter (2,000–3,000W) |
| 2 AWG | 170A | 108A | Battery to inverter (3,000–4,000W) |
| 1/0 AWG | 215A | 137A | Battery to inverter (4,000–5,000W) |
| 2/0 AWG | 265A | 167A | Battery to inverter (5,000W+) |
Voltage drop calculator
Voltage drop wastes power and can prevent batteries from charging correctly. Keep all DC runs under 3% voltage drop. The formula: Drop% = (2 × length × current × resistance per foot) ÷ voltage × 100
Cable sizing by circuit
Battery to inverter — most critical run
This carries the highest current in your system. A 2,000W inverter on 12V draws up to 167A — requiring 2/0 AWG for runs over 3 feet. Keep this run as short as possible (under 3 feet ideal).
| Inverter size | 12V system | 24V system | 48V system |
|---|---|---|---|
| 1,000W | 4 AWG | 8 AWG | 10 AWG |
| 2,000W | 2/0 AWG | 4 AWG | 8 AWG |
| 3,000W | 3/0 AWG | 2 AWG | 6 AWG |
| 5,000W | 4/0 AWG | 1/0 AWG | 4 AWG |
Solar panels to charge controller
Current here is lower than battery cables. Use the short-circuit current (Isc) of your panel string × 1.25 safety factor to size this run. MC4 connectors are rated to 30A — if your string exceeds this, split into multiple strings.
Charge controller to battery
Size to the controller's maximum output current × 1.25. A 40A controller needs cable rated for 50A minimum — typically 8 AWG for short runs, 6 AWG for longer runs.
The 18-inch fuse rule
Every cable leaving a battery must be fused within 18 inches of the battery terminal. This includes the inverter cable, the charge controller cable and any DC loads. The fuse protects the cable from overheating if a fault occurs downstream.
Cable types for solar
| Cable type | Best for | Notes |
|---|---|---|
| PV Wire / USE-2 | Panel to controller outdoor runs | UV resistant, rated for direct burial |
| THWN-2 | Conduit runs indoors/outdoors | Standard for conduit installations |
| Welding cable | Battery to inverter | Flexible, high-strand count, easy to route |
| Marine tinned copper | Boats, coastal, humid environments | Tin coating prevents corrosion |
Frequently asked questions
Can I use regular household wire for solar?
Standard NM (Romex) household wire is not rated for outdoor UV exposure or DC high-current applications. Use PV wire for outdoor panel runs and welding cable or THWN-2 for battery connections.
How do I reduce voltage drop on long runs?
Three options: (1) upsize the cable, (2) increase system voltage (12V → 24V → 48V), (3) shorten the run by relocating components. Increasing system voltage is often the most cost-effective solution for long cable runs.
What size wire for MC4 connectors?
MC4 connectors are designed for 10–12 AWG wire. The connectors are rated to 30A — size your panel strings so each string stays under 30A short-circuit current.