Motor Power Cable Size Calculator (Polycab)

Polycab Cable Size Formula:

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

Current (I):

Amps

Length (L):

Meters

Resistivity (ρ):

Ω-m

Voltage Drop (Vd):

Volts

Calculated Cross-Section Area:

Recommended Polycab Cable Size:

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1. What is the Polycab Cable Size Formula?

The Polycab cable size formula calculates the minimum cross-sectional area required for motor power cables based on current, length, resistivity, and acceptable voltage drop. It ensures safe and efficient power transmission according to Polycab standards.

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 copper (0.0000000172 Ω-m)
\( Vd \) — Acceptable voltage drop (Volts)

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

3. Importance of Proper Cable Sizing

Details: Correct cable sizing prevents overheating, ensures voltage stability, maintains efficiency, and complies with safety standards. Undersized cables can cause dangerous overheating and voltage drops.

4. Using the Calculator

Tips:

Enter motor full load current in amps
Include total cable run length (one way)
Default resistivity is for copper (0.0000000172 Ω-m)
Typical voltage drop allowance is 3-5% of supply voltage
Calculator recommends nearest standard Polycab cable size

5. Frequently Asked Questions (FAQ)

Q1: What are standard Polycab cable sizes?
A: Standard sizes include 1, 1.5, 2.5, 4, 6, 10, 16, 25, 35, 50, 70, 95, 120, 150, 185, 240, 300, 400, and 500 mm².

Q2: How do I determine motor current?
A: Check motor nameplate for full load current (FLC), or calculate as: Current (A) = Power (W) / (Voltage (V) × Power Factor × Efficiency).

Q3: What's the typical voltage drop allowance?
A: Generally 3-5% of supply voltage (e.g., 5V drop for 415V supply). Critical applications may require tighter limits.

Q4: Does this work for aluminum cables?
A: No, use resistivity of 0.0000000282 Ω-m for aluminum and consult Polycab aluminum cable specifications.

Q5: Should derating factors be applied?
A: For high ambient temperatures or bundled cables, apply appropriate derating factors from Polycab technical documents.