Voltage Drop Calculator — Formula
## 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.
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.
Exemplo Resolvido
Single phase, 30 A load, 50 m cable run, cable resistance 1.15 ohm/km.
- V_drop = 2 x 30 x 50 x 1.15 / 1000 = 3.45 V
- Percentage = 3.45 / 230 x 100 = 1.50%
- This is within the typical 3% limit.