Voltage Drop Calculator
Calculate the voltage drop in a cable run for single-phase or three-phase circuits.
Voltage Drop
3.45 V
Voltage Drop vs Load Current (I)
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.
Exemplo Resolvido
Single phase, 30 A load, 50 m cable run, cable resistance 1.15 ohm/km.
- 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.
Perguntas Frequentes
What is the maximum allowable voltage drop?
Most electrical codes allow 3% for branch circuits, 2% for feeders, and 5% total from service entry to final outlet. Some critical equipment may require tighter limits (1-2%).
How do I find cable resistance per km?
Cable manufacturers publish tables of resistance per km for each cable size and conductor material. Copper is about 60% less resistive than aluminium. Resistance increases with temperature.
What if voltage drop is too high?
Increase the cable size (lower resistance per km), reduce the cable length (relocate the panel closer), or increase the voltage (use 400V three-phase instead of 230V single-phase).
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