1. What is the Cable Size Formula?

The cable size formula calculates the minimum cross-sectional area required for electrical cables supplying motors, considering current, cable length, material resistivity, and allowed voltage drop.

2. How Does the Calculator Work?

The calculator uses the formula:

Where:

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

Explanation: The formula accounts for both the outgoing and return paths (hence the ×2 factor) and ensures the voltage drop stays within acceptable limits.

3. Importance of Proper Cable Sizing

Details: Correct cable sizing prevents excessive voltage drop (which can cause motor performance issues), overheating, and potential fire hazards. It also ensures energy efficiency and compliance with electrical codes.

4. Using the Calculator

Tips:

• For motors, use the full load current rating
• Typical resistivity values: Copper = 0.0172 Ω·mm²/m, Aluminum = 0.0282 Ω·mm²/m
• Standard voltage drop allowance is 3% of supply voltage (e.g., 3V for 100V supply)
• The calculator recommends the next standard cable size up from the calculated value

5. Frequently Asked Questions (FAQ)

Q1: Why is voltage drop important for motors?
A: Excessive voltage drop can cause motors to run hotter, reduce starting torque, and decrease efficiency.

Q2: What are common standard cable sizes?
A: Common sizes (in mm²): 1, 1.5, 2.5, 4, 6, 10, 16, 25, 35, 50, 70, 95, 120.

Q3: Should I consider other factors beyond this calculation?
A: Yes, also consider ambient temperature, installation method, short-circuit protection, and mechanical strength requirements.

Q4: How does cable length affect the calculation?
A: Longer cable runs require larger cross-sections to maintain the same voltage drop percentage.

Q5: What if my calculated size is between standard sizes?
A: Always round up to the next standard size for safety and performance.