1. What is the Cable Size Formula?

The cable size formula calculates the minimum cross-sectional area required for an electric motor cable based on current, length, material resistivity, and acceptable voltage drop. Proper sizing ensures safe operation and prevents excessive voltage drop.

2. How Does the Calculator Work?

The calculator uses the cable size formula:

Where:

• \( A \) — Cross-sectional area (mm²)
• \( I \) — Current (Amps)
• \( L \) — Cable length (meters)
• \( \rho \) — Resistivity of conductor material (Ω·mm²/m)
• \( Vd \) — Acceptable voltage drop (Volts)

Explanation: The formula accounts for both the outgoing and return paths (hence the ×2 factor) and ensures the voltage drop doesn't exceed acceptable limits.

3. Importance of Proper Cable Sizing

Details: Correct cable sizing prevents overheating, ensures proper motor operation, maintains efficiency, and reduces fire risks. Undersized cables can cause excessive voltage drop leading to motor performance issues.

4. Using the Calculator

Tips:

• For copper conductors, use ρ ≈ 0.0172 Ω·mm²/m
• For aluminum conductors, use ρ ≈ 0.0282 Ω·mm²/m
• Typical voltage drop limits are 3-5% of supply voltage
• Always round up to the nearest standard cable size

5. Frequently Asked Questions (FAQ)

Q1: Why is voltage drop important?
A: Excessive voltage drop can cause motors to run hotter, reduce efficiency, and potentially fail to start under load.

Q2: What's the typical resistivity for copper?
A: Pure copper at 20°C has ρ ≈ 0.0172 Ω·mm²/m, but this increases with temperature.

Q3: Should I include safety factors?
A: Yes, consider adding 20-25% margin to the calculated size for future loads and safety.

Q4: How does temperature affect the calculation?
A: Higher temperatures increase resistivity. For high-temp environments, use resistivity values at operating temperature.

Q5: What about three-phase systems?
A: For three-phase, the formula changes to \( A = \frac{\sqrt{3} \times I \times L \times \rho}{Vd} \).