Engineering & Physics CalcyZone Calculator

Voltage Drop Calculator

Calculate voltage drop in a copper or aluminium cable run for single-phase/DC or three-phase circuits.

Voltage drop

6.451 V

Drop %

2.8%

Voltage at load

223.55 V

Step-by-step working

R (one conductor) = ρL/A = 1.68e-8 × 30 / 2.5e-6 = 0.2016 Ω
Vd = 2 × I × R = 6.451 V

Mathematical Formula

R = ρ L / A (one conductor). Single-phase/DC: Vd = 2 I R. Three-phase: Vd = √3 I R. Drop % = Vd / V × 100. (Resistive only, 20 °C.)

Overview & Explanation

Current flowing through cable resistance loses voltage. Long runs and small conductors increase the drop.

How It Works

Compute one-conductor resistance from resistivity.
Multiply by 2 (go-and-return) or √3 (three-phase).
Compare with the supply voltage.

Practical Applications

Sizing cables for pumps, EV chargers, solar.
Checking long garden or farm runs.

Example 1: 30 m, 16 A, 2.5 mm² Cu, 230 V

Domestic circuit.

Inputs

One-way cable length (m): 30 · Load current (A): 16 · Conductor cross-section (mm²): 2.5 · Conductor: Copper (ρ = 1.68×10⁻⁸ Ω·m) · System: Single-phase / DC (2 wires) · Supply voltage (V): 230

= entered

Step 1

R (one conductor) = ρL/A = 1.68e-8 × 30 / 2.5e-6 = 0.2016 Ω

Step 2

Vd = 2 × I × R = 6.451 V

Voltage drop

Result

= 6.451 V

Example 2: 100 m, 40 A, 16 mm² Al, 415 V 3-phase

Feeder.

Inputs

One-way cable length (m): 100 · Load current (A): 40 · Conductor cross-section (mm²): 16 · Conductor: Aluminium (ρ = 2.65×10⁻⁸ Ω·m) · System: Three-phase (balanced) · Supply voltage (V): 415

= entered