Solar System Designer Tools
Solar Wire Sizing Calculator
Determine the correct AWG wire gauge for every DC circuit in your solar system — battery cables, charge controller wiring, inverter cables, and PV strings — based on current load, run length, and NEC voltage drop limits.
Why Wire Sizing Is Critical for Solar Safety
Safety Warning: Undersized wires overheat, degrade insulation, and can start fires. In DC solar systems, arcs are harder to extinguish than AC arcs. Always size wires conservatively and include appropriate overcurrent protection.
Wire sizing in solar systems follows two criteria — current carrying capacity (ampacity) and voltage drop. The larger wire required by either criterion is the one you must use.
Voltage Drop Limits
- 3% max for most DC circuits — the NEC recommended limit for branch circuits
- 1–2% for critical battery-to-inverter runs to minimize power loss
- 2% max for PV source circuits per NEC 690.8
AWG Wire Sizing Reference Table
Maximum current (amps) at 3% voltage drop for various wire gauges and run lengths at 12V:
| AWG | 5 ft run | 10 ft run | 15 ft run | 20 ft run | Ampacity (90°C) |
|---|
| 14 AWG | 29A | 14A | 10A | 7A | 25A |
| 12 AWG | 46A | 23A | 15A | 12A | 30A |
| 10 AWG | 74A | 37A | 25A | 18A | 40A |
| 8 AWG | 118A | 59A | 39A | 29A | 55A |
| 6 AWG | 188A | 94A | 62A | 47A | 75A |
| 4 AWG | 299A | 149A | 99A | 75A | 95A |
| 2 AWG | 475A | 237A | 158A | 119A | 130A |
| 1/0 AWG | 755A | 378A | 252A | 189A | 170A |
These are round-trip run length values (total wire length for both positive and negative conductors).
Frequently Asked Questions
What wire size do I need for a 2,000W inverter at 12V?
A 2,000W inverter at 12V draws up to 167A (2,000 ÷ 12 = 167A). For a 3-foot run, you need at least 2/0 AWG cable. For a 5-foot run, use 3/0 AWG. This is why 12V is not recommended for inverters over 1,000W — the required cable size and cost becomes impractical. Use 48V systems for large inverters.
How do I calculate the total run length for wire sizing?
Total run length is the round-trip distance — the length of the positive conductor plus the length of the negative conductor. If your battery is 6 feet from the inverter, the total run is 12 feet (6 ft positive + 6 ft negative). Always use this total length in the calculator.
Can I use regular household wire for solar?
No. Household NM (Romex) cable is rated for AC use and typically only 600V. Solar PV wiring requires USE-2 or PV-wire rated for wet conditions, UV exposure, and the specific voltages in your system. For DC battery circuits, use marine-grade or fine-stranded welding cable for flexibility and high-current handling.
What fuse size should I use for my solar wiring?
Fuses protect the wire, not the device. The fuse should be rated at 125% of the circuit's continuous current, and must not exceed the wire's ampacity. Install fuses as close to the positive terminal of the battery bank as possible — within 18 inches for safety.