1. What is the 3-Phase Cable Size Formula?

The 3-phase motor cable size formula calculates the minimum cross-sectional area of a cable needed to limit voltage drop to an acceptable level. Proper cable sizing ensures efficient power transmission and prevents overheating.

2. How Does the Calculator Work?

The calculator uses the formula:

Where:

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

Explanation: The formula accounts for current carrying capacity, cable length, material properties, and acceptable voltage drop to determine minimum cable size.

3. Importance of Proper Cable Sizing

Details: Correct cable sizing prevents excessive voltage drop (which can cause motor performance issues), reduces energy loss, and minimizes heat generation that could damage insulation.

4. Using the Calculator

Tips:

• Enter full load current of the motor
• Use one-way cable length (not round-trip)
• Typical resistivity: 0.0000000172 Ω·m for copper, 0.0000000282 Ω·m for aluminum
• Voltage drop should typically be 3-5% of supply voltage

5. Frequently Asked Questions (FAQ)

Q1: Why multiply length by 2 in the formula?
A: For 3-phase systems, this accounts for the vector sum of voltage drops in all three conductors.

Q2: What's the typical voltage drop allowance?
A: Generally 3-5% of supply voltage. For 400V systems, this would be 12-20V.

Q3: How does temperature affect cable sizing?
A: Higher temperatures increase resistance. For hot environments, use a higher resistivity value.

Q4: Should I round up the calculated cable size?
A: Yes, always select the next standard cable size larger than your calculation.

Q5: Does this account for starting current?
A: No, for motors with high starting current, you may need to size cables for starting conditions rather than running current.