Formula Used
Current per run = total current ÷ parallel runs.
Required ampacity = current per run × continuous current factor.
Corrected ampacity = reference ampacity × material factor × temperature factor × conduit fill factor.
DC or single phase voltage drop = 2 × current × ohms per 1000 ft × one way feet ÷ 1000.
Three phase voltage drop = √3 × current × ohms per 1000 ft × one way feet ÷ 1000.
Voltage drop percent = voltage drop ÷ system voltage × 100.
Power loss = current² × conductor path resistance.
How to Use This Calculator
- Enter the expected array current from module or inverter data.
- Enter the nominal circuit voltage used for drop checks.
- Measure one way cable distance, not round trip distance.
- Select copper or aluminum conductor material.
- Set the allowed voltage drop target.
- Add ambient temperature and conductor count for derating.
- Press calculate and review the result above the form.
- Export the record with the CSV or PDF button.
Example Data Table
| Current |
Voltage |
Length |
Material |
Drop Limit |
Recommended Size |
Drop |
Loss |
| 10 A |
48 V |
50 ft |
Copper |
3% |
10 AWG |
2.08% |
9.99 W |
| 16 A |
150 V |
120 ft |
Copper |
2% |
8 AWG |
1.61% |
38.58 W |
| 28 A |
240 V |
80 ft |
Aluminum |
3% |
6 AWG |
1.21% |
81.16 W |
Understanding PV Wire Size
PV wire size affects safety, voltage quality, and energy yield. A solar array can make steady current for many hours. That current heats the conductor. Long cable runs also add resistance. Resistance creates voltage drop and wasted power. Good sizing keeps both effects within safe limits.
Why Ampacity Matters
Ampacity is the current a conductor can carry without unsafe heating. It changes with insulation rating, ambient temperature, conductor material, and conduit fill. Copper usually carries more current than aluminum at the same size. Hot roofs reduce available ampacity. Bundled circuits inside conduit also need derating. The calculator applies these common planning adjustments. It then compares corrected ampacity with design current.
Why Voltage Drop Matters
Voltage drop is not only a comfort issue. In photovoltaic circuits, extra drop can reduce inverter input voltage. It can lower charge controller performance. It also converts solar energy into heat along the wire. Designers often target two percent or three percent on important runs. Lower drop usually needs a larger conductor. Larger wire costs more, but saves energy over time.
How This Tool Helps
The calculator checks several conductor sizes. It estimates resistance from wire data. It multiplies one way distance by the circuit path factor. Direct current and single phase circuits use a two conductor path. Three phase circuits use a square root of three factor. The tool finds the first size that passes ampacity and voltage drop limits. It also reports power loss, voltage loss, and margin.
Practical Example
A rooftop string may carry ten amps across sixty feet. Small conductors may pass ampacity, yet fail the drop target. A larger gauge can cut losses during operation. The table below shows how input changes affect the recommended size and calculated waste and heat.
Design Notes
Use the result as an engineering estimate. Real projects may require local electrical code review. Terminal ratings can limit conductor temperature. Roof exposure can need special cable ratings. Overcurrent devices must match the final design. Always verify array current from module labels and inverter documentation. Measure actual routing length, including bends and service loops. When uncertain, choose the larger listed conductor. A careful wire size protects equipment, improves production, and supports cleaner maintenance records.
FAQs
What is a PV wire size calculator?
It estimates a suitable conductor size for photovoltaic circuits. It checks voltage drop, resistance, ampacity, material, length, and basic derating factors.
Should I use one way length or round trip length?
Enter one way length. The calculator applies the circuit path multiplier for DC, single phase, or three phase voltage drop.
Why does a longer cable need a larger wire?
Longer cable has more resistance. More resistance causes higher voltage drop and power loss. Larger conductors reduce that resistance.
What voltage drop limit should I choose?
Many designers use two or three percent for important solar runs. Use stricter limits when voltage margin is small or energy loss matters.
Does copper perform better than aluminum?
Copper normally has lower resistance and higher ampacity for the same size. Aluminum can still work when sized correctly and installed properly.
Why is ambient temperature included?
High temperature reduces safe current capacity. Roof and conduit conditions can be hot, so derating gives a more cautious planning result.
Can this replace an electrical code review?
No. It is a planning calculator. Final conductor size should follow local electrical codes, product listings, terminals, and professional design review.
What does parallel runs mean?
Parallel runs split current across multiple conductor sets. The calculator divides current by the number of runs before checking each conductor path.