Voltage Drop Calculator Formula
Understand the math behind the voltage drop calculator. Each variable explained with a worked example.
Formulas Used
Voltage Drop
vdrop = factor * current * cable_length * resistance / 1000Voltage Drop %
vdrop_pct = factor * current * cable_length * resistance / 1000 / supply_voltage * 100Variables
| Variable | Description | Default |
|---|---|---|
current | Load Current (I)(A) | 30 |
cable_length | One-Way Cable Length(m) | 50 |
resistance | Cable Resistance(ohm/km) | 1.15 |
supply_voltage | Supply Voltage(V) | 230 |
phases | Phase Configuration | 1 |
factor | Derived value= (phases == 1) ? 2 : sqrt(3) | calculated |
How It Works
Cable Voltage Drop
Voltage drop occurs as current flows through the resistance of cable conductors.
Formulas
Single phase: V_drop = 2 I L R_cable / 1000
Three phase: V_drop = sqrt(3) I L R_cable / 1000
where I is current, L is one-way length in metres, and R_cable is resistance in ohms/km. The factor of 2 in single-phase accounts for the return conductor. Most codes limit voltage drop to 3-5% of supply voltage.
Worked Example
Single phase, 30 A load, 50 m cable run, cable resistance 1.15 ohm/km.
current = 30cable_length = 50resistance = 1.15supply_voltage = 230phases = 1
- 01V_drop = 2 x 30 x 50 x 1.15 / 1000 = 3.45 V
- 02Percentage = 3.45 / 230 x 100 = 1.50%
- 03This is within the typical 3% limit.
Ready to run the numbers?
Open Voltage Drop Calculator