Solar Calculator
Solar Wire Size Calculator
Created By
Willmar Furgesin
Choosing the correct wire size for your solar system is essential for safety, efficiency, and performance. Our Solar Wire Size Calculator helps you find the ideal wire gauge based on your system voltage, load current, cable length, and allowable voltage drop. Whether you’re wiring a 12V DC solar setup, 24V, or 240V AC system, this tool ensures you use the right wire size for your installation.
How to Use the Cable Size Calculator
Using the solar wire size calculator is simple. Just enter the values for each field below:
1. Load Current (Amps)
Enter the total current your circuit will carry. If you don’t know the amps, use the formula:
Amps = Watts ÷ Volts
For example, a 240W solar panel running at 12V draws 20A (240 ÷ 12 = 20A).
2. Length
Add the total cable run length — from the power source (solar panel, inverter, or battery) to the device. For DC circuits, always use the round-trip distance (out and back).
3. Units
Select the measuring unit (feet or meters) for your cable length.
4. System Voltage (V)
Choose your system’s voltage — common values are 12V, 24V, 48V, 120V, or 240V. Higher voltage systems generally allow thinner wire for the same power level.
5. Allowable Voltage Drop (%)
Voltage drop is the small amount of voltage lost as electricity flows through the wire. Most solar setups use 2–3% as a safe limit. The calculator adjusts the wire size automatically based on your chosen percentage.
6. Circuit Type
Select whether it’s a DC system or an AC system. For DC systems, both positive and negative conductors are considered in voltage drop calculations.
7. Ambient Temp (°C)
Enter the average operating temperature. Higher temperatures reduce wire capacity. The calculator applies NEC (National Electrical Code) correction factors.
8. Wire Bundle Size
If multiple wires are grouped together, heat buildup occurs. The calculator will automatically derate ampacity based on the number of conductors bundled.
Once you enter all the details, click Calculate, and you’ll instantly get the recommended wire size (AWG) suitable for your system.
How to Calculate Wire Size (Formula)
For DC systems, wire sizing is based on the voltage drop formula:
A=2×L×I×ρΔVA = \frac{2 × L × I × ρ}{ΔV}
Where:
A = Wire cross-sectional area (m²)
L = One-way cable length (meters)
I = Load current (amps)
ρ = Resistivity of conductor (ohm·meter)
ΔV = Allowable voltage drop (volts)
This formula is used internally by the solar wire size calculator to ensure your setup meets safe voltage drop and ampacity limits.
DC Cable Sizing Formula (Practical Example)
Let’s say you have:
System Voltage: 12V DC
Load Current: 20A
Length: 30 feet (round-trip 60 ft)
Voltage Drop: 3% (0.36V)
Using the formula, the calculator determines that 8 AWG copper wire will safely handle this load with minimal voltage loss.
This same principle applies to 24V and 48V systems. higher voltages mean lower current, which allows smaller gauge wire.
Rated Amps for Wire Size (Copper, 60°C Rating)
| Wire Gauge (AWG) | Max Amps | Typical Use Case |
|---|---|---|
| 14 AWG | 15A | Small DC loads, lighting |
| 12 AWG | 20A | Medium 12V solar circuits |
| 10 AWG | 30A | Inverter connections, 12V/24V |
| 8 AWG | 40A | Long 12V runs, small inverters |
| 6 AWG | 55A | High-load DC systems |
| 4 AWG | 70A | 24V/48V battery connections |
| 2 AWG | 95A | Large inverter cables |
| 1/0 AWG | 125A | 48V heavy-duty solar wiring |
12 Volt Wiring Size Chart (3% Voltage Drop, Copper)
| Amps | 10 ft | 20 ft | 30 ft | 40 ft | 50 ft |
|---|---|---|---|---|---|
| 5A | 16 AWG | 14 AWG | 14 AWG | 12 AWG | 12 AWG |
| 10A | 14 AWG | 12 AWG | 10 AWG | 10 AWG | 8 AWG |
| 15A | 12 AWG | 10 AWG | 8 AWG | 8 AWG | 6 AWG |
| 20A | 10 AWG | 8 AWG | 6 AWG | 6 AWG | 4 AWG |
This chart helps you visually match your system current, distance, and voltage drop allowance.
For 24V or 48V systems, wire size requirements decrease proportionally because current halves or quarters at higher voltages.
240 Volt Wire Size Chart (NEC Reference)
| Load Current (A) | Wire Gauge (AWG) | Typical Use |
|---|---|---|
| 15A | 14 AWG | Standard lighting |
| 20A | 12 AWG | Receptacles, outlets |
| 30A | 10 AWG | Small appliances |
| 40A | 8 AWG | Electric water heater |
| 50A | 6 AWG | Electric range |
| 70A | 4 AWG | Sub-panel feeder |
| 100A | 2 AWG | Main breaker feeder |
For long-distance 240V runs, increase the wire size to limit voltage drop under 3% (≈7.2V).
How to Calculate Wire Size for Amps?
Divide watts by volts to get current. Then use the calculator or chart to pick the wire gauge that supports that current with acceptable voltage drop.
What Is the DC Cable Sizing Formula?
The DC formula calculates wire area based on voltage drop:
A = (2 × L × I × ρ) / ΔV.
Our calculator automates this for copper and aluminum conductors.
Why Is Voltage Drop Important?
Excessive voltage drop wastes power and reduces system performance. Keeping it below 3% ensures efficient energy transfer.
Can I Use Aluminum Wires?
Yes, but aluminum wires have higher resistance. Always size aluminum one step larger than copper for the same amp load.
What’s the Safety Margin?
he NEC recommends wires be rated 125% of your continuous current to prevent overheating.
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Ready to Optimize Your Solar Panels?
There are several online calculators can help you simplify solar instalation and mentainance. Among the most accurate calculators, SolarSCalculator.com is the best resource to offer online calculators.