Voltage drop calculator

Calculate voltage drop and size wires appropriately

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The Voltage Drop Calculator helps electrical engineers and electricians determine voltage drop in electrical circuits and verify wire sizes meet code requirements. Calculate voltage loss based on wire size, length, and current load.

Excessive voltage drop causes equipment to operate inefficiently and can damage motors and electronics. Electrical codes limit voltage drop to 3-5% depending on circuit type. Proper wire sizing ensures adequate voltage at load points.

Enter system voltage, current load, wire length, and wire size to calculate voltage drop percentage. The calculator helps select appropriate wire sizes to maintain acceptable voltage levels and ensures code-compliant electrical installations.

Features

Everything you need

Voltage drop calculations
Wire size recommendations
Multiple voltage system support
Round-trip distance calculations
Code compliance checking
Wire resistance database
Warning indicators for excessive drop

How it works

Simple workflow

1
Enter system voltage (120V, 208V, 240V, 480V)
2
Input current load in amperes
3
Specify wire length (one-way)
4
Select wire size (AWG)
5
Review calculated voltage drop percentage

Use cases

Built for real-world scenarios

Circuit design

Size wires for new electrical circuits to ensure acceptable voltage drop.

Code compliance

Verify voltage drop meets NEC requirements (3% for feeders, 5% total).

Motor circuits

Ensure adequate voltage for motor starting and operation.

Long circuit runs

Determine wire size requirements for circuits with long conductor lengths.

FAQ

Frequently asked questions

Voltage Drop = I × R × 2, where I is current, R is resistance per foot, and 2 accounts for round-trip (hot and neutral). Resistance depends on wire size and material (copper vs. aluminum).

NEC recommends maximum 3% drop for feeders, 5% total (feeder + branch). For 120V circuits: max 3.6V drop (3%) or 6V total (5%). Excessive drop causes equipment problems.

Larger wire (lower AWG number) has less resistance and lower voltage drop. Doubling wire size (e.g., 12 AWG to 10 AWG) approximately halves resistance and voltage drop.

Select wire size based on ampacity (current capacity) and voltage drop. If voltage drop exceeds limits, increase wire size even if ampacity is adequate. The calculator helps identify when upsizing is needed.

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We're always looking to improve our calculators. If you have ideas for new features, improvements, or found something that could work better, we'd love to hear from you.

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