Cable Size for 7.5kW 3 Phase Motor

Cable Size Formula:

\[ A_w = \frac{I \times L \times K}{V_{drop} \times \sigma} \]

Current (I):

amps

Cable Length (L):

Correction Factor (K):

Voltage Drop (V_drop):

volts

Conductivity (σ):

Ω⁻¹·mm²/m

Cable Size (A_w):

Unit Converter ▲

Unit Converter ▼

From:	To:

1. What is Cable Size Calculator for 7.5kW 3 Phase Motor?

Definition: This calculator determines the appropriate cable size (cross-sectional area) needed for a 7.5kW three-phase motor installation.

Purpose: It helps electricians and engineers select the correct cable gauge to ensure safe operation and acceptable voltage drop.

2. How Does the Calculator Work?

The calculator uses the formula:

\[ A_w = \frac{I \times L \times K}{V_{drop} \times \sigma} \]

Where:

\( A_w \) — Cable cross-sectional area (mm²)
\( I \) — Current (amps)
\( L \) — Cable length (ft)
\( K \) — Correction factor (typically 1.25 for motors)
\( V_{drop} \) — Acceptable voltage drop (volts)
\( \sigma \) — Conductivity of copper (58 Ω⁻¹·mm²/m)

Explanation: The formula calculates the minimum cable size needed to carry the motor current while maintaining acceptable voltage drop over the cable length.

3. Importance of Proper Cable Sizing

Details: Correct cable sizing prevents overheating, ensures efficient operation, and maintains motor performance by limiting voltage drop.

4. Using the Calculator

Tips: Enter motor current (typically 15A for 7.5kW at 400V), cable length, correction factor (default 1.25), acceptable voltage drop (default 3V), and conductivity (default 58 for copper).

5. Frequently Asked Questions (FAQ)

Q1: How do I find the motor current?
A: For 7.5kW at 400V 3-phase: \( I = \frac{7500}{400 \times \sqrt{3} \times 0.85} \approx 15A \) (PF assumed 0.85)

Q2: Why is voltage drop important?
A: Excessive voltage drop causes motor overheating and reduces starting torque.

Q3: When would I change the correction factor?
A: Adjust for ambient temperature (>30°C use 1.1), cable grouping, or insulation type.

Q4: What's typical conductivity for cables?
A: Copper: 58 Ω⁻¹·mm²/m, Aluminum: 36 Ω⁻¹·mm²/m.

Q5: Does this include safety margins?
A: The correction factor provides some margin, but consult local regulations for full requirements.