Voltage Drop Wire Size Calculator

Advanced Wire Size Form

Example Data Table

Formula Used

DC voltage drop: Vd = 2 × I × L × R

Single phase voltage drop: Vd = 2 × I × L × (R × PF + X × sinθ)

Three phase voltage drop: Vd = √3 × I × L × (R × PF + X × sinθ)

Drop percentage: Drop % = Voltage Drop ÷ System Voltage × 100

Resistance is adjusted for conductor temperature. Parallel conductors reduce effective resistance.

How to Use This Calculator

Enter voltage, current, and one way conductor length. Select the circuit type, material, power factor, temperature, and allowed drop. Choose a specific wire size when you want to review it. Leave that field blank when you want automatic selection. Press the calculate button. The result appears below the header and above the form.

Voltage Drop Wire Size Guide

Why Voltage Drop Matters

Voltage drop is the loss of voltage across a conductor. It happens because every wire has resistance. Long runs and heavy loads increase this loss. A small drop is normal. A large drop can reduce performance. Motors may run hotter. Lights may dim. Equipment may fail to start correctly.

Choosing a Better Wire Size

This calculator compares common wire sizes. It checks resistance, length, current, material, and circuit type. It then finds the first size that meets the selected drop limit. Copper usually gives lower resistance than aluminum. Aluminum often needs a larger size for similar performance.

Single Phase and Three Phase Loads

Different systems use different equations. A direct current circuit uses the outgoing and return conductor path. A single phase circuit also considers the full loop path. A three phase circuit uses the square root of three. Power factor is included for alternating current loads.

Temperature and Parallel Runs

Conductor resistance changes with heat. Hot conductors have higher resistance. That can increase voltage drop. The calculator adjusts resistance by temperature. Parallel conductors share current. They reduce effective resistance. They can improve voltage drop on large feeders.

Practical Design Notes

Many designers aim for three percent on branch circuits. Feeders may use a separate design target. Local rules can vary. Always compare the result with code requirements. Ampacity, insulation rating, terminals, conduit fill, and protection devices also matter. This tool supports planning. It should not replace a qualified electrical review.

Exporting Results

The CSV button saves the comparison table. The PDF button creates a simple report. These exports help with records, estimates, and design checks. You can test different currents, lengths, and materials. Then compare the recommended sizes before choosing a final conductor.

FAQs

What is voltage drop?

Voltage drop is voltage lost as current moves through wire resistance. It increases with longer length, higher current, and smaller conductor size.

Why does wire size affect voltage drop?

Larger wire has lower resistance. Lower resistance reduces voltage loss and helps connected equipment receive better operating voltage.

Does copper perform better than aluminum?

Copper has lower resistance than aluminum. For the same current and length, copper usually gives lower voltage drop.

What is a good voltage drop limit?

Many designs use three percent as a practical target. Some sensitive equipment may need a lower drop target.

Does the calculator check ampacity?

Yes. It compares estimated ampacity with load current. Still, final ampacity must follow local electrical rules.

Why is power factor included?

Power factor affects alternating current voltage drop. Motors and inductive loads often need this extra adjustment.

Can I use this for three phase feeders?

Yes. Select the three phase option. The calculator then applies the three phase voltage drop equation.

Is this result final for installation?

No. Use it for planning. Final conductor selection should include code, terminals, insulation, conduit, and protection checks.