Recommended Wire Size
| Item | Value |
|---|
Advanced Wire Sizing Tool
Enter load, distance, material, phase, derating, and raceway details. The calculator compares ampacity sizing and voltage-drop sizing, then recommends the larger conductor.
Example Data Table
| Example | Load | Voltage | Length | Material | Target Drop | Typical Result |
|---|---|---|---|---|---|---|
| Small branch circuit | 20 A | 120 V | 50 ft | Copper | 3% | 12 AWG estimate |
| Workshop feeder | 60 A | 240 V | 125 ft | Copper | 3% | 4 AWG estimate |
| Long aluminum feeder | 100 A | 240 V | 175 ft | Aluminum | 3% | 1/0 AWG or larger estimate |
Formula Used
The calculator first converts the entered load into amperes. For single phase AC, it uses
I = P ÷ (V × PF). For three phase AC, it uses
I = P ÷ (√3 × V × PF). For DC, it uses I = P ÷ V.
Continuous loads are multiplied by 125% when selected. Corrected ampacity is calculated as
Corrected Ampacity = Table Ampacity × Ambient Factor × Conductor Count Factor × Custom Factor.
Voltage drop is estimated with conductor resistance. For DC and single phase circuits, the path multiplier is 2.
For three phase circuits, the multiplier is √3. AC voltage drop may include the entered reactance value:
VD = Multiplier × I × L × (R × PF + X × sinθ) ÷ 1000.
How to Use This Calculator
- Select the load input type and enter the load value.
- Enter voltage, phase type, power factor, and length.
- Choose copper or aluminum and the temperature rating column.
- Add ambient temperature and current-carrying conductor count.
- Select a maximum voltage-drop target, such as 3%.
- Enter raceway details for a basic fill estimate.
- Click calculate and review the larger required size.
- Download CSV or PDF for records and design notes.
Wire Size Planning Guide
Why Wire Size Matters
Wire size affects safety, performance, and energy loss. A conductor must carry the expected current without overheating. It must also keep voltage drop within a useful range. Long runs need special attention. Small conductors have more resistance. More resistance creates more heat and more voltage loss. That can reduce motor starting torque. It can also make lights dim and equipment run poorly.
Ampacity Comes First
Ampacity is the safe current capacity of a conductor under stated conditions. Material, insulation temperature, ambient heat, and raceway grouping all affect it. Copper usually carries more current than aluminum of the same gauge. Higher temperature insulation may allow a higher table value. Terminals may still limit the usable column. This is why field verification is important.
Voltage Drop Comes Next
Voltage drop is not the same as ampacity. A wire can be safe by ampacity and still lose too much voltage on a long run. The calculator checks both requirements. It finds the first size that meets derated ampacity. It also finds the first size that meets the selected voltage-drop limit. The final recommendation is the larger of those two sizes.
Derating and Raceway Fill
Multiple current-carrying conductors in one raceway can trap heat. Hot ambient conditions can also reduce capacity. This tool applies common adjustment factors for planning. It also estimates raceway fill using stored conductor areas. Treat this as an early check, not a final installation schedule.
Practical Design Notes
Use actual load data whenever possible. Use nameplate current for motors and equipment. Use expected continuous loading when the circuit runs for long periods. Select conservative values when details are uncertain. Confirm breaker size, equipment terminals, insulation type, grounding conductors, raceway fill, and local code rules before installation.
FAQs
1. What does this wire size calculator estimate?
It estimates a conductor size from load current, distance, voltage, material, derating, and voltage drop. It compares ampacity and voltage-drop needs.
2. Is the result a final code approval?
No. It is a planning result only. Final approval depends on the adopted code, local amendments, equipment ratings, and inspection requirements.
3. Why does length change the result?
Longer conductors have more total resistance. More resistance creates more voltage drop. A larger conductor can reduce that drop.
4. Why can voltage drop require a larger wire?
A wire may carry current safely but still lose too much voltage. Long circuits often need upsizing for performance, not only heat.
5. Why choose copper or aluminum?
Copper has lower resistance and higher ampacity for many sizes. Aluminum is lighter and often cheaper, but usually needs a larger size.
6. What is continuous load sizing?
A continuous load runs for a long duration. Many designs size conductors and overcurrent protection at 125% of that load.
7. What does current-carrying conductor count do?
Grouped conductors create more heat. The calculator applies an adjustment factor when several current-carrying conductors share a raceway.
8. Can I download the result?
Yes. Use the CSV button for spreadsheet records. Use the PDF button for a printable design summary.