Cable Size Calculator
Calculate the minimum required cable cross-sectional area (mm²) to ensure safe current carrying capacity and keep voltage drop within acceptable limits.
How to Calculate Cable Size
Sizing a cable correctly is crucial for electrical safety and efficiency. If a cable is too small, it will overheat and cause a severe voltage drop, leading to equipment failure. The cross-sectional area is determined primarily by the resistivity of the metal and the maximum allowable voltage drop.
The Voltage Drop Formula
For standard electrical installations, the minimum cross-sectional area (A) is calculated using the following formulas.
For DC and Single-Phase AC Systems:
$$A = \frac{2 \cdot L \cdot I \cdot \rho}{V_d}$$For Three-Phase AC Systems:
$$A = \frac{\sqrt{3} \cdot L \cdot I \cdot \rho}{V_d}$$Where:
- A = Minimum cross-sectional area in mm²
- L = Length of the cable in meters
- I = Load current in Amps
- ρ = Resistivity of the conductor (Copper ≈ 0.01724, Aluminum ≈ 0.0282)
- Vd = Allowable voltage drop in Volts (e.g., 3% of 230V = 6.9V)
Frequently Asked Questions
What is a standard acceptable voltage drop?
According to standard electrical codes (like the NEC and IEC), a voltage drop of 3% is recommended for branch and lighting circuits, and up to 5% is acceptable for overall power circuits.
Should I choose Copper or Aluminum?
Copper has lower resistivity and handles more current for the same physical size, making it standard for residential wiring. Aluminum is cheaper and lighter, making it ideal for long utility transmission lines or heavy industrial feeders.