Cable Size for 30kW Motor Calculator

Cable Size Formula:

\[ A = \frac{I \times L \times 2 \times \rho}{Vd} \] \[ I = \frac{30,000}{\sqrt{3} \times V \times PF \times \eta} \]

Voltage (V):

Power Factor (PF):

Efficiency (η):

Cable Length (L):

meters

Resistivity (ρ):

ohm-m

Voltage Drop (Vd):

Calculated Current (I):

Required Cross-Section (A):

Recommended Cable Size:

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1. What is the Cable Size Calculation?

The cable size calculation determines the appropriate conductor cross-sectional area for a 30kW motor based on current, cable length, material resistivity, and allowable voltage drop. Proper sizing ensures safe operation and prevents overheating.

2. How Does the Calculator Work?

The calculator uses two main formulas:

\[ A = \frac{I \times L \times 2 \times \rho}{Vd} \] \[ I = \frac{30,000}{\sqrt{3} \times V \times PF \times \eta} \]

Where:

\( A \) — Cable cross-section area (mm²)
\( I \) — Current (A)
\( L \) — Cable length (meters)
\( \rho \) — Resistivity of conductor material (ohm-m)
\( Vd \) — Allowable voltage drop (V)
\( V \) — System voltage (V)
\( PF \) — Power factor
\( \eta \) — Motor efficiency

Explanation: First calculates the current drawn by the motor, then determines the minimum cable size needed to limit voltage drop.

3. Importance of Proper Cable Sizing

Details: Correct cable sizing prevents voltage drop issues, overheating, energy loss, and potential fire hazards. It also ensures motor starting and running performance.

4. Using the Calculator

Tips: Enter system voltage (typically 400V for 3-phase), power factor (usually 0.8-0.9), motor efficiency (typically 0.85-0.95), cable length, conductor resistivity (0.0000000172 ohm-m for copper), and acceptable voltage drop (typically 3-5% of system voltage).

5. Frequently Asked Questions (FAQ)

Q1: Why calculate for 30kW specifically?
A: This is a common motor size in industrial applications. The same method can be adapted for other motor sizes.

Q2: What's typical resistivity for copper?
A: 0.0000000172 ohm-m for copper at 20°C. For aluminum, use 0.0000000282 ohm-m.

Q3: What voltage drop is acceptable?
A: Generally 3-5% of nominal voltage (12-20V for 400V systems) for motors.

Q4: Why multiply length by 2?
A: This accounts for both the live and neutral conductors in single-phase systems. For 3-phase, the factor is actually √3 but we use 2 as a conservative estimate.

Q5: What are standard cable sizes?
A: Common sizes are 1.5, 2.5, 4, 6, 10, 16, 25, 35, 50, 70, 95, 120, 150, 185, 240, 300 mm².