Southwire Cable Size Calculator

Southwire Cable Size Formula:

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

Length (L):

Current (I):

Resistivity (ρ):

Ω·m

Voltage Drop (Vd):

Cable Size (A):

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1. What is the Southwire Cable Size Formula?

The Southwire cable size formula calculates the minimum cross-sectional area of a cable needed to carry a specific current over a certain distance while maintaining an acceptable voltage drop. This ensures electrical systems operate efficiently and safely.

2. How Does the Calculator Work?

The calculator uses the Southwire formula:

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

Where:

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

Explanation: The formula calculates the minimum cable size needed to ensure the voltage drop doesn't exceed the specified limit, maintaining proper voltage at the load.

3. Importance of Proper Cable Sizing

Details: Proper cable sizing is crucial for electrical safety, preventing overheating, ensuring efficient power transmission, and maintaining equipment performance. Undersized cables can cause voltage drops, overheating, and potential fire hazards.

4. Using the Calculator

Tips: Enter cable length in meters, current in amperes, resistivity in ohm-meters (copper is typically 1.68×10⁻⁸ Ω·m), and maximum allowable voltage drop in volts. All values must be positive numbers.

5. Frequently Asked Questions (FAQ)

Q1: Why is the factor 2 used in the formula?
A: The factor 2 accounts for the round trip length of the circuit (both the hot and neutral/return conductors).

Q2: What is a typical acceptable voltage drop?
A: For most applications, a voltage drop of 3% or less is acceptable for branch circuits, and 5% or less for feeder circuits.

Q3: How does temperature affect cable sizing?
A: Higher temperatures increase conductor resistance, which may require larger cable sizes. The calculator uses resistivity at standard temperature (usually 20°C).

Q4: Are there other factors to consider besides voltage drop?
A: Yes, also consider ampacity (current-carrying capacity), short-circuit protection, installation method, and ambient temperature when selecting cable size.

Q5: Can this calculator be used for both AC and DC systems?
A: This formula works for both AC and DC systems, though for AC systems, additional factors like power factor and skin effect may need consideration for precise calculations.