Southwire Cable Sizing Calculator

Southwire Cable Sizing Formula:

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

Length (L):

Current (I):

Resistivity (ρ):

Ω·m

Voltage Drop (Vd):

Cross-Sectional Area (A):

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1. What is the Southwire Cable Sizing Formula?

The Southwire cable sizing formula calculates the minimum cross-sectional area of a cable needed to limit voltage drop to an acceptable level. It's based on the fundamental electrical principles of resistance and voltage drop in conductors.

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 (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 conductor size needed to maintain voltage drop within acceptable limits for a given current and cable length.

3. Importance of Proper Cable Sizing

Details: Proper cable sizing is crucial for electrical safety, efficiency, and compliance with electrical codes. Undersized cables can cause excessive voltage drop, overheating, and potential fire hazards.

4. Using the Calculator

Tips: Enter cable length in meters, current in amperes, conductor 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: What is the typical resistivity value for copper?
A: The resistivity of copper at 20°C is approximately 1.68×10⁻⁸ Ω·m.

Q2: What is an acceptable voltage drop for electrical circuits?
A: Most electrical codes recommend a maximum voltage drop of 3% for branch circuits and 5% for feeder circuits.

Q3: Does this formula account for temperature variations?
A: The basic formula uses resistivity at standard temperature. For precise calculations, temperature correction factors should be applied.

Q4: Why is there a factor of 2 in the formula?
A: The factor of 2 accounts for the round-trip path of current (both the hot and neutral/ground conductors).

Q5: Can this calculator be used for both AC and DC systems?
A: This formula is primarily for DC systems. For AC systems, additional factors like power factor and skin effect should be considered.