12 AWG Solar Installation Wire Run-Length and Power-Loss Cheat Sheet

Why Voltage Drop Matters

• Efficiency & Performance: Every foot of wire adds electrical resistance, causing some voltage to be “lost” as heat rather than delivered to your inverter, charge controller, or batteries.
• Lower Voltage Circuits Are More Affected: At 12 V or 24 V, even a few volts dropped can represent a large percentage of the total.
• High Current & Long Runs Amplify Losses: Doubling the distance roughly doubles the voltage drop, while higher current also increases the drop proportionally.

Assumptions & Key Points

1. Wire Resistance: Based on Solar Super Sonic 12 AWG (UL4703, 2 kV) PV wire with max. resistance @ 1.60 Ω per 1000 ft.
2. Distances Listed: 6 ft, 10 ft, 20 ft, 30 ft, 50 ft, 100 ft, 150 ft, 200 ft, and 400 ft (one-way). The round-trip distance is 2 × (one-way).
3. Currents: Showcasing with 5 A, 10 A, 15 A, 20 A, and 30 A systems. Actual current will vary by scenario. Wire gauges should be calculated using maximum anticipated currents and should be protected with fuses or other safety devices
4. Voltage Drop Formula: $$V_{\text{drop}} = I \;\times\; R_{\text{wire}}\;\times\;\frac{\text{Round-Trip Distance}}{1000}$$ where $R_{\text{wire}}$ = 1.60 Ω/1000 ft (for 12 AWG).
5. Percentage Drop: $$\%\text{Drop} = \Bigl(\frac{V_{\text{drop}}}{V_{\text{system}}}\Bigr)\times 100\%$$ We show columns for 12 V, 24 V, 48 V, 100 V, 240 V, 600 V, 1000 V, 1500 V
   
6. Disclaimers:
   • Real-world factors (e.g., temperature, humidity) will impact the actual voltage drop.
   • Always consult the National Electrical Code (NEC) or local guidelines for safe and compliant installations.
   • These tables illustrate trends. If you see very high percentages, you likely need thicker wire or higher system voltage.

Table A: 12 AWG @ 5 A

Table B: 12 AWG @ 10 A

Table C: 12 AWG @ 15 A

Table D: 12 AWG @ 20 A

• (100 ft @12 V => 53.33% is still <100, so it remains.
• (200 ft @12 V => 106.67% => “>99%”; 24 V => 53.33% => <100.
• (400 ft @12 V => 213.33% => “>99%”; 24 V => 106.67% => “>99%”.)

Table E: 12 AWG @ 30 A

Conclusions & Tips

1. Beware of High % Drops at 12 V & 24 V

   • Even moderate distances become impractical above ~20 A if you want to keep voltage drop under 3–5%.

2. Increasing System Voltage Decreases % Loss

   • If you’re designing larger or commercial PV systems, consider 48 V, 100 V, or even higher DC bus voltages.

3. Use Thicker Wire for Long Runs

   • If these tables show excessive losses, you may need 10 AWG or 8 AWG (or thicker) for acceptable efficiency.

4. Check Code Requirements

   • The National Electrical Code (NEC) and local regulations have ampacity, overcurrent, and conduit fill rules that might require larger gauges regardless of voltage-drop considerations.

By consulting these cheat-sheets, you can quickly see whether 12 AWG wire is suitable for your run length, current, and voltage. Generally, NEC recommends a voltage drop of 3% or less. If higher drop observed than desired, it’s time to shorten the cable runs, bump up wire size, or raise the system voltage to keep your solar installation efficient and code-compliant.