CONDUCTORS · CALCULATOR

Maximum wire length (voltage drop)

Free maximum wire length (voltage drop): get maximum one-way length from voltage, current, conductor area, resistivity at operating temperature and drop limit.

Written by Chameera Sampath · Not yet reviewed by a licensed electrician. See the methodology.

US (NEC) only · NFPA 70 / NEC — locally adopted editionDefaults are US values. Verify the locally adopted NEC edition and project data.Official reference ↗

Project inputs

Measurements

Voltage

Current

Conductor area

kcmil

Resistivity at operating temperature

Ω·cmil/ft

Drop limit

Supply

Set area from AWG (geometric equivalent)

Resistivity starting point:Override with project temperature / manufacturer data.

Updates as inputs change. Unit changes preserve the same physical values.

THE MATH BEHIND THE ANSWER

Method & assumptions

Lmax = A × V × limit / (100 × k × I × ρ)

Resistance-only, voltage-drop limit. Separately verify protection and ampacity.

Results do not check every aspect of an electrical installation. The calculators follow US (NEC) practice only; a regional preset changes defaults such as voltage and units, and no result certifies NEC compliance.

Sources and validation →

Worked example

Voltage: 120 V · Current: 20 A · Conductor area: 6.53 kcmil · Resistivity at operating temperature: 12.9 Ω·cmil/ft · Drop limit: 3 % · Supply: Single phase

Maximum one-way length: 45.558 ft

This example uses the stated inputs; results for the entered values appear above.

Explore the conductors branch →See the related electrical concepts →

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