DC Solar Cable Size Calculator
Calculate PV string cable size using solar panel current, number of parallel strings and cable distance. Determine proper DC solar wire size and voltage drop instantly.
🌞 Free Tool · No Signup · Instant Results
DC Solar String Cable Size Calculator
Calculate DC cable size between solar panel strings and inverter or combiner box using solar module current and installation distance.
Results follow NEC 690 solar installation standards. Use UV resistant solar PV cable rated for outdoor installation.
How to Use DC Solar Cable Size Calculator
Correctly sizing the cables in your photovoltaic system prevents energy loss, reduces heat generation, and ensures compliance with local electrical codes. Getting your DC cable size took less than a minute. Follow these simple steps:
- Step 1: Open solar panel datasheet. Locate the parameters for maximum power current (Imp) and short circuit current (Isc).
- Step 2: Enter panel Isc value. Type in the Short Circuit Current (Isc) in Amps.
- Step 3: Enter panel Imp value. Input the Maximum Power Current (Imp) in Amps.
- Step 4: Enter number of panels per string. Specify the panels wired in series in a single string.
- Step 5: Enter number of parallel strings. Input the total number of parallel solar strings merging onto the main DC run.
- Step 6: Input cable distance. Enter the one-way distance between the solar panel array and the inverter or combiner box, choosing meters or feet.
- Step 7: Choose cable material. Select Copper or Aluminum depending on your conductor specifications.
- Step 8: Select voltage drop. Select your allowable voltage drop (1%, 2%, or 3%). Keeping voltage drop under 2% is ideal for DC power transmission.
- Step 9: Click calculate. Hit the calculate button to see the required cable size in mm², recommended AWG wire gauge, design currents, and actual operating voltage drops instantly.
⚠️ Note Box
More parallel strings increase current and usually require larger cable size to handle the combined amperage safely and maintain low voltage drop.
How to Calculate DC Solar Cable Size
Solar cable sizing depends mainly on string current, cable run length and voltage drop limits. The engineering calculations follow standard physical equations to determine the minimum cable cross-sectional area that prevents thermal losses and excessive voltage drops.
1. Calculate Solar String Current
When wiring panels in series, the current remains constant. However, combining multiple strings in parallel sums their currents:
2. Calculate Design Current
The National Electrical Code (NEC) requires sizing conductors for 125% of continuous load currents to provide a safe buffer for intense sun conditions:
3. Cable Size Formula
The copper or aluminum cross-sectional area (A) in square millimeters is determined using the two-way loop run length, design current, material resistivity, and maximum allowable voltage drop:
Where:
- A: Required cable cross-section in mm²
- L: One-way cable run distance (converted to meters)
- ρ (Resistivity): Conductor electrical resistivity. Copper = 0.01724 Ω·mm²/m; Aluminum = 0.0282 Ω·mm²/m
- Vd: Allowable voltage drop in volts ($V_{string} \times \text{allowable drop percentage}$)
Step-by-Step Calculation Example
Let's take a practical solar installation with the following specifications:
- Panel Imp: 13 A
- Parallel Strings: 3
- Panels per String: 6
- Panel Vmp: 35 V
- Cable Distance: 25 m (Copper conductor, 2% allowable drop, 1.25 safety factor)
Step 1: Calculate String & Design Current
Idesign = 39 A × 1.25 = 48.75 A
Step 2: Calculate String Voltage & Voltage Drop Limit
Vd_allowable = 210 V × (2 / 100) = 4.2 V
Step 3: Calculate Cross-Sectional Area (A)
Rounding up to the next commercial size yields a 10 mm² PV cable, which maps exactly to an 8 AWG wire. This matches the target requirements perfectly.
Factors Affecting Cable Size
To avoid fire hazards and high system losses, several parameters must be evaluated together during sizing:
- Parallel Strings: Adding strings in parallel multiplies current, which requires significantly thicker conductors.
- Panel Current: Higher power modules release more amps under standard testing, raising requirements.
- Cable Distance: Longer cables cause higher resistance, amplifying voltage drops and requiring oversized wires.
- Voltage Drop: Choosing stricter drop limits (1% instead of 3%) increases efficiency but requires larger cable sizes.
- Material Type: Aluminum has higher electrical resistance than copper, meaning an aluminum conductor needs to be approximately 60% larger in cross-sectional area to carry the same current.
- Ambient Temperature: Outdoor PV wires exposed to hot roofs undergo thermal resistance increases and require thermal de-rating factors.
Solar String Cable Size Chart
Use this reference chart to identify typical recommended copper solar string cable sizes based on string amperage and run length. Sizing is designed to maintain a voltage drop below 2% for a standard 240V DC solar array using premium copper conductors.
| Current (A) | Cable Length (m) | Cable Size (mm²) | Recommended AWG |
|---|---|---|---|
| 10 A | 15 m | 4 mm² | 12 AWG |
| 20 A | 20 m | 6 mm² | 10 AWG |
| 40 A | 25 m | 10 mm² | 8 AWG |
| 60 A | 30 m | 16 mm² | 6 AWG |
| 80 A | 35 m | 25 mm² | 4 AWG |
| 100 A | 40 m | 35 mm² | 2 AWG |
| 125 A | 50 m | 50 mm² | 1/0 AWG |
* Always verify cable size with local electrical code requirements and manufacturer recommendations. Ground-mount and roof-mount systems have distinct thermal exposure conditions.
DC Solar Cable Size Calculator FAQs
Cable size depends on solar string current, cable distance and allowable voltage drop. Sizing is based on the formula: A = (2 × L × Idesign × ρ) / Vd, where A is the required cable cross-section in mm², L is the distance, Idesign is the operating current multiplied by a safety factor (typically 1.25), ρ is the conductor material resistivity, and Vd is the maximum allowable voltage drop in Volts.
Imp (maximum power current) represents the operating current of the solar panel under peak load conditions. Since the solar panel operates near Imp during peak sunlight, it is the most accurate value to determine the actual continuous current running through the solar string cables.
Parallel strings combine current from multiple strings, increasing the total current running through the main DC run to the inverter or combiner box. Because current increases while voltage remains constant in parallel configurations, a larger cable size is required to handle the higher amperage and keep voltage drop within safe limits.
A 1% to 3% voltage drop is commonly used for sizing solar PV systems. Keeping the voltage drop at 2% or less is recommended to maximize system efficiency, minimize power losses, and ensure optimal performance of the solar inverter.
Yes, this calculator is suitable for solar string cable sizing applications, including the cables between individual solar panels in series, as well as the main DC feed cables between a combiner box and the solar inverter.