Cable Size Calculator Southwire

Cable Size Equation:

\[ A = \frac{2 \times L \times I \times \rho}{Vd} \]

Length (L):

Current (I):

Resistivity (ρ):

ohm m

Voltage Drop (Vd):

Cable Size (A):

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1. What is the Cable Size Equation?

The Cable Size Equation calculates the appropriate cable cross-sectional area based on voltage drop considerations. It ensures that the voltage drop in an electrical circuit remains within acceptable limits for proper equipment operation.

2. How Does the Calculator Work?

The calculator uses the cable size equation:

\[ A = \frac{2 \times L \times I \times \rho}{Vd} \]

Where:

\( A \) — Cable cross-sectional area (mm²)
\( L \) — Length of the cable (m)
\( I \) — Current flowing through the cable (A)
\( \rho \) — Resistivity of the conductor material (ohm m)
\( Vd \) — Maximum allowable voltage drop (V)

Explanation: The equation calculates the minimum cable size needed to maintain voltage drop within specified limits, considering the cable length, current load, and material properties.

3. Importance of Cable Size Calculation

Details: Proper cable sizing is essential for electrical safety, energy efficiency, and preventing equipment damage due to excessive voltage drop. It ensures compliance with electrical codes and standards.

4. Using the Calculator

Tips: Enter cable length in meters, current in amperes, resistivity in ohm meters, and maximum allowable voltage drop in volts. All values must be positive numbers.

5. Frequently Asked Questions (FAQ)

Q1: What is the typical resistivity value for copper?
A: The resistivity of copper is approximately 1.724 × 10⁻⁸ ohm m at 20°C.

Q2: What is the typical resistivity value for aluminum?
A: The resistivity of aluminum is approximately 2.82 × 10⁻⁸ ohm m at 20°C.

Q3: What is an acceptable voltage drop percentage?
A: Most electrical codes recommend a maximum voltage drop of 3-5% for branch circuits and 1-2% for feeder circuits.

Q4: Why is the factor 2 included in the formula?
A: The factor 2 accounts for the round-trip path of current (both out and return conductors) in a single-phase AC or DC circuit.

Q5: Does this formula work for three-phase systems?
A: For balanced three-phase systems, the formula becomes \( A = \frac{\sqrt{3} \times L \times I \times \rho}{Vd} \), using the same units.