Calculator Inputs
Example Data Table
| Load | Phase | Voltage | Current | Length | Material | Drop Limit | Typical Result |
|---|---|---|---|---|---|---|---|
| Outdoor pump | Single phase | 240 V | 32 A | 180 ft | Copper | 3% | Review larger conductors |
| Shop feeder | Three phase | 480 V | 80 A | 250 ft | Aluminum | 3% | Compare kcmil sizes |
| Battery circuit | DC | 48 V | 60 A | 35 ft | Copper | 2% | Short runs matter |
Formula Used
Single phase AC: Voltage drop = 2 × I × (R × PF + X × sinθ) × L / 1000.
Three phase AC: Voltage drop = √3 × I × (R × PF + X × sinθ) × L / 1000.
Direct current: Voltage drop = 2 × I × R × L / 1000.
Temperature correction: R adjusted = R table × [1 + α × (T − 75)].
Percent drop: Voltage drop % = Voltage drop ÷ source voltage × 100.
R is resistance in ohms per 1000 feet. X is reactance in ohms per 1000 feet. L is one way length in feet. PF is power factor. Parallel conductors divide resistance and increase total ampacity.
How To Use This Calculator
- Select single phase, three phase, or direct current.
- Choose copper or aluminum conductor material.
- Enter voltage, current, and one way circuit length.
- Set the allowed voltage drop percentage.
- Enter conductor temperature and power factor.
- Add reactance for AC runs when known.
- Enter parallel conductors if the run uses them.
- Press calculate and review the first passing wire size.
- Download CSV or PDF results for project records.
Voltage Drop And Wire Size Guide
Voltage drop is the loss of electrical pressure along a conductor. It rises when current, distance, or resistance increases. A small drop is normal. A large drop can reduce motor torque, dim lights, heat conductors, and waste energy. This calculator helps you compare conductor sizes before you buy cable or pull wire.
Why Wire Size Matters
Wire size affects both voltage drop and ampacity. A larger conductor has lower resistance. It can deliver a steadier voltage at the load. Long branch circuits, feeders, pumps, welders, chargers, and outdoor runs often need a larger conductor than the minimum ampacity size. The result should still be checked against local code, terminal ratings, insulation type, and protection devices.
How The Calculator Works
The tool starts with phase type, source voltage, load current, conductor material, run length, temperature, and power factor. It then tests each wire size in order. For alternating current, it can include a reactance value. For direct current, it uses resistance only. Parallel conductors are handled by dividing resistance and current between conductors. The first size that meets the selected voltage drop limit is shown as the recommended size.
Choosing A Drop Limit
Many designers use three percent for branch circuits and five percent for feeders plus branches. Sensitive electronics, lighting, and starting motors may need a tighter limit. Remote loads may need a budget balance. Larger wire costs more, but it can lower losses and improve performance. The calculator shows voltage lost, percent drop, load voltage, estimated loss, and annual energy cost, so you can compare options.
Practical Design Notes
Use one way circuit length, not round trip length. Select copper or aluminum carefully. Aluminum needs compatible terminals and proper workmanship. Choose the temperature near the conductor operating condition. Enter a realistic power factor for motors and transformers. Treat results as planning help. Final wire selection should follow electrical codes and a qualified professional review.
Reading The Output
The table lets you inspect smaller and larger sizes quickly. Green or warning colors are not required here, so the text states whether each choice passes. Save the CSV for spreadsheets. Save the PDF for simple job notes and customer files. Review assumptions before installation starts.
FAQs
1. What is voltage drop?
Voltage drop is the voltage lost as current moves through wire resistance. Longer wires, higher current, and smaller conductors usually increase the drop.
2. What voltage drop limit should I use?
Many designs use 3% for branch circuits. Feeders plus branch circuits are often kept near 5%. Sensitive loads may need less.
3. Should I enter one way length?
Yes. Enter the one way distance from source to load. The calculator applies the return path factor for single phase and direct current.
4. Does this replace electrical code?
No. It is a planning tool. Final conductor selection must follow local code, protection rules, terminal ratings, and qualified review.
5. Why include power factor?
Power factor affects AC voltage drop. Motors and transformers often have lower power factors than heaters or simple resistive loads.
6. What does reactance mean?
Reactance is opposition caused by AC magnetic effects. It matters more on larger feeders, long runs, and three phase systems.
7. Why does temperature matter?
Conductor resistance changes with temperature. Hotter conductors usually have higher resistance, which can increase voltage drop.
8. Can I use parallel conductors?
Yes. Enter the number of parallel conductors per phase. Installations must use matching lengths, materials, sizes, and proper terminations.