Formula Used
Current from power: I = P / V for DC or single phase AC.
Three phase current: I = P / (sqrt(3) × V × PF).
Allowed voltage drop: Vdrop = system voltage × drop percent / 100.
DC or single phase area: A = 2 × rho × L × I / Vdrop.
Three phase area: A = sqrt(3) × rho × L × I / Vdrop.
Design current: Id = I × continuous factor × margin factor.
Derated ampacity: ampacity × ambient derate × conduit derate × parallel conductors.
Here, rho is conductor resistivity. Copper uses 0.017241 ohm mm2 per meter. Aluminum uses 0.028264 ohm mm2 per meter.
How to Use This Calculator
Enter the project name first. Select DC, single phase, or three phase. Add system voltage and load current. If current is unknown, enter watts. Enter the one way cable length. Pick feet or meters. Choose the allowed voltage drop. Then set material, insulation rating, derating values, and parallel conductors. Press Calculate. The result appears above the form.
Example Data Table
| Use Case |
Voltage |
Current |
One Way Length |
Drop Target |
Material |
| Panel string to controller |
150 V |
12 A |
60 ft |
2% |
Copper |
| Battery to inverter |
48 V |
125 A |
8 ft |
1% |
Copper |
| Combiner to equipment room |
300 V |
32 A |
120 ft |
3% |
Aluminum |
Solar Cable Planning Basics
Solar wire sizing protects energy yield and equipment. A cable can carry current and still waste power. Long runs make this worse. A small conductor adds resistance. Resistance creates heat and voltage drop. The calculator compares both limits. It helps choose a practical conductor before final design review.
Why Voltage Drop Matters
Panels, charge controllers, batteries, and inverters work best inside voltage limits. If voltage drops too far, a controller may harvest less power. A battery cable may heat during high current. An inverter may alarm during surge loads. Keeping drop near two or three percent is common for many solar runs. Critical battery leads often need an even lower value.
Ampacity and Derating
Ampacity is the current a conductor can carry safely. It depends on conductor size, metal, insulation rating, ambient temperature, conduit fill, and local rules. Derating reduces the listed ampacity when heat cannot escape well. Solar circuits are often continuous loads, so designers add a safety multiplier. This tool applies a continuous factor, margin, and two derating entries.
Copper and Aluminum
Copper has lower resistance than aluminum. It normally gives a smaller conductor for the same drop. Aluminum can cost less for large feeders, but it needs correct terminals, antioxidant practices, and careful torque. The calculator supports both metals. It reports area in square millimeters and a common gauge label.
Practical Use
Enter the one way distance, not the round trip length. Choose the circuit type. Add voltage and current. You may enter watts instead of current. For three phase AC, include power factor. Pick the allowed voltage drop. Then set material, insulation rating, and derating values. The result shows the minimum area and the first listed size that passes voltage drop and ampacity checks.
Result Review
Review the loss percentage beside the selected size. If energy loss is high, shorten the route, raise system voltage, or choose a larger cable before ordering wire or trenching conduit.
Design Reminder
This calculator is for planning and education. It does not replace electrical code, conductor temperature tables, equipment labels, or a licensed installer. Solar systems can produce dangerous current. Confirm overcurrent protection, terminal ratings, grounding, conduit fill, temperature corrections, and local inspection rules before installation.
FAQs
What wire size should I use for solar panels?
It depends on current, voltage, distance, material, and allowed voltage drop. Enter those values in the calculator. The result gives a planning size that passes voltage drop and ampacity checks.
Should solar wire sizing use one way or round trip distance?
Enter one way distance. The calculator handles round trip resistance for DC and single phase circuits. Three phase circuits use the standard square root of three voltage drop factor.
Is copper better than aluminum for solar wiring?
Copper has lower resistance, so it usually needs a smaller conductor. Aluminum may cost less for large feeders. It needs compatible lugs, correct torque, and proper installation practices.
What voltage drop is acceptable for solar cables?
Many designers target two or three percent. Battery and inverter cables may need lower drop. Sensitive equipment, long runs, or high current circuits need closer review.
Why does derating change the recommended size?
Derating lowers usable ampacity when heat builds up. High ambient temperature, conduit fill, and bundled conductors can require larger wire even when voltage drop looks acceptable.
Can I enter watts instead of amps?
Yes. Leave current blank and enter watts. The calculator estimates current from voltage. For three phase AC, it also uses the power factor value.
Does this calculator replace electrical code?
No. It is a planning tool. Always confirm conductor ampacity, overcurrent protection, terminal temperature ratings, grounding, conduit fill, and local inspection rules before installation.
What are parallel conductors?
Parallel conductors share current in larger circuits. The calculator divides area and ampacity needs across them. Use parallel conductors only when allowed by code and equipment ratings.