Calculator Input
Formula Used
Base current = panel Isc × parallel strings, or direct array current.
Design current = base current × current factor × (1 + safety margin ÷ 100).
Allowed voltage drop = system voltage × voltage drop percent ÷ 100.
Resistance adjusted for temperature = ρ20 × [1 + α × (conductor temperature - 20)].
Required area = circuit factor × adjusted resistance × distance × design current ÷ allowed voltage drop.
The circuit factor is 2 for DC and single phase runs. It is √3 for three phase runs.
The final recommendation must pass both voltage drop and corrected ampacity checks.
How to Use This Calculator
- Choose whether current comes from panel Isc and strings, or a direct array current.
- Enter system voltage, one way route length, and the maximum voltage drop.
- Select copper or aluminum, circuit type, insulation rating, and temperatures.
- Enter the current factor, safety margin, and conductor grouping value.
- Press the calculate button and review the result above the form.
- Use the CSV or PDF button to save the result for project records.
Example Data Table
| Example | Voltage | Current | Distance | Drop Limit | Material | Likely Result |
|---|---|---|---|---|---|---|
| Small cabin array | 48 V | 28 A | 25 m | 3% | Copper | Check result with temperature settings |
| Long garden shed run | 120 V | 18 A | 55 m | 2% | Copper | Larger cable may be required |
| Aluminum feeder | 240 V | 50 A | 40 m | 3% | Aluminum | Compare ampacity and drop |
About Solar Cable Sizing
A solar panel cable size calculator helps you match wire area with current, distance, material, and allowed voltage drop. Correct sizing protects energy yield and reduces heat in long outdoor runs. It also supports better inverter performance because the inverter receives a steadier voltage under load.
Why Voltage Drop Matters
Every cable has resistance. When current flows, part of the panel voltage is lost as heat. A small drop is normal, but a high drop wastes generated power. Many designers target about one to three percent for important solar circuits. Shorter cables, thicker conductors, and higher system voltage can reduce the loss.
Current and Safety Factor
Solar conductors often carry current for many hours. That makes continuous current sizing important. This calculator lets you multiply array current by a user selected factor. A common design value is 1.25, but local rules may require a different method. Extra margin can also be added for future changes, aging, or warmer site conditions.
Material and Temperature
Copper and aluminum have different resistivity. Aluminum normally needs a larger area for the same voltage drop. Temperature also matters. Hot conductors resist current more than cool conductors. The tool adjusts resistance with conductor temperature and also checks ampacity using ambient temperature and grouped conductor correction factors.
Using the Result
The recommended size is selected only when it passes both voltage drop and corrected ampacity checks. The voltage drop check estimates the needed cross sectional area. The ampacity check compares design current with the corrected table value. If no size is found, reduce distance, raise voltage, lower drop demand, or use a larger cable table.
Good Installation Practice
Calculator results are design aids, not final approvals. Real projects must follow local electrical codes, product listings, terminal temperature limits, and inspection rules. Consider conduit fill, rooftop heat, combiner ratings, fuse sizes, and inverter manual limits. For large arrays or commercial work, ask a qualified solar professional to verify the design.
Planning Tips
Measure the real one way route, not a straight drawing distance. Include bends, drops, and service loops. Keep positive and negative conductors together where possible. Record assumptions beside the result so later maintenance teams clearly understand the chosen cable size safely.
FAQs
What does this calculator estimate?
It estimates cable size from current, distance, voltage, material, temperature, and allowed voltage drop. It also checks corrected ampacity, so the suggested cable is not based on voltage drop alone.
Can I use it for DC solar strings?
Yes. Select the DC two wire option and enter one way cable length. The calculator doubles the run length internally because current travels through positive and negative conductors.
Why is the current factor included?
Solar conductors can carry current continuously. The current factor lets you add a design multiplier, such as 1.25, before checking voltage drop and ampacity.
Why does aluminum need a larger cable?
Aluminum has higher resistivity than copper. For the same current and distance, it produces more voltage drop, so a larger cross sectional area is usually required.
What voltage drop should I choose?
Many small solar designs use one to three percent. Lower drop improves energy delivery, but it can require larger cable. Always follow project rules and local code.
Does this replace electrical code?
No. It is a design aid. Final cable selection must match local electrical code, equipment listings, terminal ratings, protection devices, and inspection requirements.
Why can no cable size be found?
The selected table may not contain a cable large enough for both voltage drop and corrected ampacity. Try lower distance, higher voltage, relaxed drop, or a larger conductor table.
What length should I enter?
Enter the one way physical route from the source to the load or inverter. Include bends, vertical drops, conduit paths, and service loops, not just map distance.