Three Phase Voltage Drop Calculator

Calculator

Enter values, press submit, then review results shown above this form.

System & load

Line-to-line voltage (V) Load entry mode

Current (A)

Power factor (0–1) Power factor type Allowable drop (%)

Run details

Length

Parallel runs per phase

Resistance and reactance are divided by this count.

Conductor material Conductor data method

For final design, prefer manufacturer impedance at operating temperature.

Cable impedance

Size unit

Conductor area (mm²)

Use nominal cross-sectional area.

Operating temperature (°C) Reactance assumption

R is estimated as DC resistance adjusted for temperature; X is a planning assumption unless you enter manufacturer data.

Reset

Tip: If you have cable datasheets, use Custom R/X for best accuracy.

Example data table

These sample rows show typical planning scenarios and rounded results.

System (V)	Load	Length	Cable	Vdrop (V)	Drop (%)
400	100 A, PF 0.85 lag	120 m	Copper 35 mm², X=0.08 Ω/km	10.13	2.53
480	60 kW, PF 0.90 lag, η 0.95	250 m	Aluminum 70 mm² @60°C, X=0.09 Ω/km	16.85	3.51
11000	150 A, PF 0.80 lag	2 km	Overhead planning, R=0.20 Ω/km, X=0.35 Ω/km	192.26	1.75
400	80 A, PF 0.90 lead	100 m	Copper 50 mm² @40°C, X=0.08 Ω/km	4.15	1.04

Formula used

Balanced three-phase voltage drop is estimated from line current and per-phase impedance.

Current from power:

I = P / ( √3 · V_LL · PF · η )

P in watts, V_LL in volts, PF is power factor, η is efficiency.

Three-phase voltage drop (line-to-line):

ΔV = √3 · I · ( R · cosφ ± X · sinφ )

Use + for lagging PF, − for leading PF. R and X are total per-phase values over the run.

Percent drop:

ΔV% = ( |ΔV| / V_LL ) · 100

Conductor losses:

P_loss = 3 · I² · R

Notes: Size-based resistance uses DC resistivity adjusted with a temperature coefficient. Reactance depends strongly on spacing, cable construction, and installation method.

How to use this calculator

Enter your system line-to-line voltage and the run length.
Select a load mode: current (A) or power (kW) with efficiency.
Set power factor and choose lagging or leading behavior.
Choose size-based estimate or enter custom R/X from your datasheet.
Set parallel runs if multiple conductors share each phase.
Press Submit to see voltage drop, percent drop, losses, and maximum length.
Use Download CSV or PDF to save the calculation record.

Article

Voltage drop targets in practice

Many facilities set a feeder drop target near 3% and a combined feeder-plus-branch target near 5%. At 400 V, a 3% limit equals 12 V. The calculator reports both volts and percent, so you can compare directly with project specifications and commissioning checks.

Current, power factor, and efficiency

When you enter kW, the tool converts to current using I = P /(√3·VLL·PF·η). For example, 60 kW at 480 V, PF 0.90, and η 0.95 produces about 84.2 A. A lower power factor increases current and raises both voltage drop and I²R losses.

Resistance, temperature, and material choice

Conductor resistance changes with operating temperature. Using copper at 40°C instead of 20°C increases resistance by roughly 7.9% with α≈0.00393/°C. Aluminum uses a higher resistivity and a slightly different temperature coefficient, so equal-area aluminum typically yields higher drop unless the size is increased.

Reactance assumptions and leading power factor

For planning, typical cable reactance ranges around 0.08–0.09 Ω/km for close-spaced cables, while overhead lines can be far higher depending on spacing. The drop term uses R·cosφ ± X·sinφ. With leading PF, the reactive term can reduce the net drop, and in rare cases the receiving voltage can rise slightly.

Parallel runs and scaling behavior

Parallel conductors divide both R and X by the number of runs, assuming equal sharing. Two identical runs halve impedance, cutting voltage drop roughly in half at the same current. Losses also drop because Ploss = 3·I²·R, and R falls with each added parallel path. If losses are 2 kW during 3,000 hours annually, wasted energy is 6,000 kWh, significantly impacting operating cost.

Using results for sizing decisions

The maximum-length output estimates how far you can run before reaching the allowable percent drop at the entered load. If your actual length exceeds that value, increase conductor size, add parallel runs, improve power factor, or raise system voltage. Always validate with manufacturer impedance data for final design.

FAQs

Plain answers for common design questions.

1. Should I enter one-way length or circuit length?

Enter the one-way route length from source to load. The three-phase formula already accounts for phase conductors; do not double the length unless your impedance data requires it.

2. Why does leading power factor reduce voltage drop?

With leading power factor, the reactive component of current is reversed. The X·sinφ term subtracts instead of adds, which can lower net drop when reactance is significant.

3. What R and X values should I use for final design?

Use manufacturer positive-sequence impedance at the operating temperature and installation method. Planning presets are useful early, but datasheet values improve accuracy and compliance.

4. Does the tool include harmonics or unbalance?

No. It assumes balanced sinusoidal current and steady-state conditions. If harmonics or unbalance are present, additional heating and neutral currents may change losses and voltage behavior.

5. How do parallel runs affect results?

Parallel runs reduce effective R and X by the number of identical conductors sharing each phase. This typically reduces voltage drop and losses, provided current shares evenly in practice.

6. Why can receiving voltage increase slightly?

If power factor is strongly leading and reactance is large, the reactive term can outweigh the resistive term, producing a negative ΔV. This indicates voltage rise at the load in the simplified model.