Formula audit
See the path multiplier, resistance/reactance, power factor and exact phasor terms behind the result.
OneFreePlace · Tool #152
Voltage drop with the cable physics exposed.
Calculate drop, plan a minimum conductor size, or find a maximum one-way run. Use copper or aluminum with temperature-adjusted resistance, AWG/kcmil or metric sizes, parallel conductors, or enter a cable datasheet's R/X directly for a power-factor-aware AC phasor check.
✓ DC + 1φ + balanced 3φ✓ AWG / kcmil / mm²✓ Cu + Al temperature correction✓ Custom R + X✓ Size + distance planners
Voltage Drop Calculator
drop · minimum size · maximum distance · exact phasor check
Calculation engine
Solve the constraint that matters.
Circuit and loadAC power-factor calculations assume a lagging/inductive load. Three-phase mode assumes a balanced line-to-line system.
Current is used directly.
Cable runLength is one-way from source to load, not the round-trip conductor length.
Conductor modelMaterial mode calculates DC resistance from cross-sectional area and temperature. Datasheet mode accepts cable R/X directly.
Copper uses ρ20 = 1.7241×10⁻⁸ Ω·m and α20 = 0.00393/K. Aluminum uses ρ20 = 2.8264×10⁻⁸ Ω·m and α20 = 0.00403/K. Temperature correction is linear around 20°C.
Enter resistance/reactance at the operating condition from the cable or conductor datasheet. Values are divided by the number of parallel conductors.
Voltage-drop result
Calculating—
voltage drop
Enter valid circuit and conductor values.
Drop percentage—exact phasor magnitude where AC applies
Load-end voltage—calculated terminal voltage
Load current—used by the drop calculation
Conductor resistance—per conductor, one-way run
Resistive line loss—I²R heating in line conductors
Target / headroom—user-selected planning target
Voltage-drop modelVoltage drop is only one conductor-sizing constraint. Verify ampacity, insulation, protection and local rules separately.
Approximation vs phasor result
For AC, the common R·cosφ + X·sinφ approximation is shown beside the exact sending/receiving voltage phasor check used for the primary result.
Size sensitivity
Material mode compares nearby standard conductor sizes. This is voltage-drop analysis only and does not assert ampacity compliance.
| Size | Area | R @ temp | Drop | Drop % | Load V | Line loss |
|---|
Planning diagnostics
See theoretical area, parallel-path effect, line efficiency and the assumptions that materially affect the result.
What changes the answer?
Conductor temperatureMetal resistance rises as conductor temperature rises. Material mode corrects resistance from the 20°C reference.
R changesPower factor and reactanceOn AC circuits, cable reactance and load power factor affect the sending-to-receiving voltage relationship. Datasheet mode exposes both R and X.
AC effectParallel conductorsIdentical parallel paths divide conductor R and X by the number of paths, assuming approximately equal current sharing.
1 / NImportant boundaries
Not an ampacity calculatorA conductor can meet a voltage-drop target and still be unsuitable for current, temperature, fault duty or installation conditions.
Separate checkBalanced 3-phase assumptionThree-phase calculations assume balanced phase currents and a line-to-line source voltage.
Model limitCustom impedance quality mattersFor large conductors, long AC runs or steel raceways, cable datasheet/table R and X can be more representative than a geometry-only resistance model.
Use datai
This tool deliberately separates voltage drop from code-based conductor selection.The minimum-size result means “smallest built-in standard area meeting the entered drop target under this electrical model.” It does not mean the conductor is acceptable for ampacity, short-circuit protection, installation method or any jurisdiction's electrical code.