AC Wire Size Calculator
Formula Used
Single phase voltage drop: VD = 2 × I × D × R × PF
Three phase voltage drop: VD = √3 × I × D × R × PF
Voltage drop percent: VD% = VD ÷ Voltage × 100
Continuous load current: Design Current = Load Current × 1.25
I is current. D is one way distance. R is conductor resistance. PF is power factor. The calculator checks ampacity and voltage drop.
How to Use This Calculator
- Enter the AC circuit voltage.
- Enter the load current in amperes.
- Add one way cable distance.
- Select single phase or three phase power.
- Choose copper or aluminum conductor material.
- Set the allowed voltage drop percentage.
- Adjust derating factors if needed.
- Press the calculate button.
Example Data Table
| Voltage | Current | Distance | Phase | Material | Max Drop | Suggested Size |
|---|---|---|---|---|---|---|
| 120 V | 15 A | 50 ft | Single | Copper | 3% | 10 AWG |
| 240 V | 25 A | 75 ft | Single | Copper | 3% | 8 AWG |
| 480 V | 40 A | 100 ft | Three | Aluminum | 3% | 4 AWG |
Wire Size for AC Circuits
Why Wire Size Matters
Wire size is important in every AC circuit. A small conductor can heat quickly. A long run can also lose voltage. Both problems reduce safety and performance. This calculator gives a practical estimate before final design.
Current and Distance
Current is the main load value. Higher current needs a larger conductor. Distance also matters because resistance increases with length. A short branch circuit may pass ampacity rules. A long feeder may still need a larger wire because the voltage drop becomes too high.
Single Phase and Three Phase
AC systems are commonly single phase or three phase. Single phase calculations use the out and return path. Three phase calculations use a different multiplier. The calculator applies the selected phase method automatically.
Voltage Drop
Voltage drop is the difference between source voltage and load voltage. Motors, heaters, lights, and tools may work poorly when voltage is low. Many designers target a small drop for branch circuits and feeders. This calculator lets you choose your own percentage.
Material Choice
Copper usually carries current with less resistance than aluminum. Aluminum can still be useful in feeders and larger services. The calculator adds a material factor to reflect higher aluminum resistance. Always use terminals rated for the selected conductor.
Derating Factors
Heat, conduit fill, bundling, and continuous load rules can reduce usable ampacity. This tool includes simple derating fields. They help you estimate a safer design current. Use local electrical codes for final approval.
Best Use
Use the result as a planning guide. Check breaker size, insulation rating, ambient temperature, installation method, and code tables before buying wire. A licensed electrician should verify critical installations.
FAQs
What is an AC wire size calculator?
It estimates a suitable conductor size for an AC circuit. It checks current, distance, phase, material, derating, and voltage drop.
Does this calculator replace electrical code tables?
No. It is a planning tool. Always compare the result with local code, breaker rating, insulation rating, and installation rules.
Why does distance affect wire size?
Longer wire has more resistance. More resistance creates more voltage drop. A longer run may need a larger conductor.
What voltage drop should I use?
Many designs use 3% as a common target. Sensitive equipment or long runs may need a lower value.
Why is continuous load multiplied by 1.25?
Continuous loads run for long periods. A safety margin helps reduce overheating risk and supports common electrical design practice.
Is copper better than aluminum?
Copper has lower resistance for the same size. Aluminum can be economical for larger feeders when properly installed.
Can I use this for motors?
Yes, for rough planning. Motors may need special rules for starting current, overload protection, and branch circuit sizing.
Why is my suggested wire larger than expected?
The calculator may increase size because of voltage drop, derating, continuous load adjustment, or aluminum conductor resistance.