Voltage Drop Calculator (NEC) | Maker Label Studio

Project Inputs

Distances are one-way feet; conductor sizes use standard circular mil values.

System voltage

Volts, line-to-line for three-phase.

Phase

Load current

Amps.

One-way distance

Feet from source to load.

Conductor material

Conductor size

AWG and larger kcmil sizes by circular mil area.

Results

Enter valid inputs to calculate voltage drop.

Awaiting inputs

Voltage drop

Volts

Percent drop

Of system voltage

3% branch target

NEC informational target

5% total target

Feeder plus branch target

Selected conductor

Material constant

Formula multiplier

Input summary

Suggested upsize

Complete the inputs to see conductor sizing guidance.

Formula: single-phase Vdrop = 2 x K x I x D / CM; three-phase Vdrop = 1.732 x K x I x D / CM. Percent drop = Vdrop / systemV x 100.

Self-Tests

Runs golden checks against the voltage-drop calculation functions.

Self-tests have not been run.

About the Voltage Drop Calculator (NEC)

Electricians, engineers, solar installers, and maintenance teams use a voltage drop calculator to estimate conductor loss before pulling wire or troubleshooting long runs. Enter voltage, phase, current, distance, conductor material, and wire size to calculate volts lost and percentage drop. It supports NEC-informed design decisions for feeders, branch circuits, motors, and low-voltage equipment.

How it works

Enter source voltage, load current, circuit length, and phase type.

Select copper or aluminum and the conductor size.

Calculate voltage drop in volts and as a percentage.

Compare the result with project limits and NEC informational note guidance.

Confirm ampacity, terminals, temperature rating, and overcurrent protection separately.

Frequently asked questions

What voltage drop does the NEC recommend?

NEC informational notes commonly reference a maximum 3% drop for branch circuits and 5% total for feeders plus branch circuits for reasonable efficiency. Informational notes are guidance unless adopted by a specification or local rule.

Is voltage drop the same as conductor ampacity?

No. Ampacity is the safe current-carrying capacity of a conductor, while voltage drop is performance loss over distance. A conductor can be code-compliant for ampacity but still have excessive voltage drop.

Why does circuit length matter so much?

Longer conductors have more resistance, so voltage drop increases with distance and current. Single-phase calculations include the full circuit path, while three-phase formulas use the appropriate phase relationship.

Can I fix voltage drop by increasing breaker size?

No. A larger breaker does not reduce conductor resistance and may create an unsafe or noncompliant installation. Use larger conductors, shorter runs, adjusted voltage, or redesigned loads where appropriate.

Does the calculator replace NEC conductor sizing?

No. Final design must also check ampacity, correction factors, terminal ratings, grounding, conduit fill, equipment instructions, and local code adoption.