Motor Power Cable Size Calculator (3 Phase)

3-Phase Cable Size Formula:

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

Current (I):

Amps

Cable Length (L):

meters

Resistivity (ρ):

Ω·m (Copper: ~0.0172)

Allowed Voltage Drop (Vd):

Volts

Required Cable Cross-Section Area (A):

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

The 3-phase cable size formula calculates the minimum cross-sectional area required for a cable to safely carry current over a specified distance while maintaining acceptable voltage drop levels. It considers current, cable length, material resistivity, and allowed voltage drop.

2. How Does the Calculator Work?

The calculator uses the formula:

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

Where:

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

Explanation: The formula accounts for both the forward and return paths (hence the factor of 2) in a 3-phase system, ensuring the voltage drop stays within acceptable limits.

3. Importance of Proper Cable Sizing

Details: Proper cable sizing is crucial for electrical safety, efficiency, and performance. Undersized cables can cause excessive voltage drop, overheating, and potential fire hazards, while oversized cables are unnecessarily expensive.

4. Using the Calculator

Tips:

Enter motor current in amps (check motor nameplate)
Measure actual cable run length (not straight-line distance)
Use 0.0172 Ω·m for copper or 0.0282 Ω·m for aluminum
Typical voltage drop limits are 3-5% of supply voltage

5. Frequently Asked Questions (FAQ)

Q1: What's the difference between 3-phase and single-phase calculations?
A: 3-phase calculations account for balanced loading across three conductors, while single-phase considers two conductors (line and neutral).

Q2: How does temperature affect the calculation?
A: Higher temperatures increase resistivity. For hot environments, use higher resistivity values (e.g., 0.0181 Ω·m for copper at 50°C).

Q3: Should I round up the calculated cable size?
A: Yes, always round up to the nearest standard cable size available (e.g., 2.5mm², 4mm², 6mm², etc.).

Q4: What about cable bundling or conduit fill?
A: These factors may require further derating. Consult electrical codes for grouping factors when multiple cables run together.

Q5: Does this account for starting current?
A: No, this is for continuous operation. For motors, you may need to check voltage drop during starting separately.