1. What is the Southwire Equation?

The Southwire equation calculates the minimum wire cross-sectional area needed to maintain a specified voltage drop over a given length for a particular current. This is crucial for electrical system design to ensure proper voltage at the load.

2. How Does the Calculator Work?

The calculator uses the Southwire equation:

Where:

• \( A \) — Cross-sectional area (m²)
• \( I \) — Current (A)
• \( \rho \) — Resistivity of copper (1.68 × 10⁻⁸ Ω·m)
• \( L \) — Length of wire (m)
• \( V_{drop} \) — Maximum allowable voltage drop (V)

Explanation: The equation accounts for the round-trip length of wire (hence ×2) and the material's resistivity to determine the minimum wire size that will keep voltage drop within acceptable limits.

3. Importance of Proper Wire Sizing

Details: Correct wire sizing prevents excessive voltage drop (which can cause equipment malfunction), reduces energy loss, and minimizes fire hazards from overheating.

4. Using the Calculator

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

5. Frequently Asked Questions (FAQ)

Q1: What resistivity value is used?
A: The calculator uses 1.68 × 10⁻⁸ Ω·m for copper at 20°C. For aluminum, use 2.65 × 10⁻⁸ Ω·m.

Q2: Why multiply length by 2?
A: The factor of 2 accounts for the round-trip path of current (out to load and back).

Q3: What's a typical acceptable voltage drop?
A: For most applications, 3% for branch circuits and 5% for feeder circuits is recommended.

Q4: Does this account for temperature effects?
A: No, this uses resistivity at 20°C. For higher temperatures, resistivity increases by about 0.4% per °C.

Q5: How do I select standard wire gauge?
A: Round up to the nearest standard wire size (AWG or mm²) that meets or exceeds the calculated area.