1. What is the Motor Wire Sizing Formula?

The wire sizing formula calculates the minimum cross-sectional area of wire needed for an AC motor circuit based on current, length, material resistivity, and acceptable voltage drop. Proper wire sizing ensures safe operation and prevents excessive voltage drop.

2. How Does the Calculator Work?

The calculator uses the wire sizing equation:

Where:

• \( A \) — Wire cross-sectional area (mm²)
• \( I \) — Current in amps
• \( L \) — Length of wire in meters (one way)
• \( \rho \) — Resistivity of wire material (ohm-m)
• \( Vd \) — Acceptable voltage drop in volts

Explanation: The equation accounts for the round-trip distance (hence ×2), material properties, and ensures voltage drop stays within acceptable limits.

3. Importance of Proper Wire Sizing

Details: Correct wire sizing prevents overheating, ensures proper motor operation, maintains efficiency, and meets electrical code requirements. Undersized wires can cause dangerous voltage drops and overheating.

4. Using the Calculator

Tips: Enter current in amps, length in meters, material resistivity (default is 0.0000000172 ohm-m for copper), and maximum acceptable voltage drop. All values must be positive numbers.

5. Frequently Asked Questions (FAQ)

Q1: What's the typical voltage drop allowance?
A: For motors, 3% voltage drop is common for branch circuits, 5% for feeders. Check local electrical codes.

Q2: What resistivity value should I use?
A: Copper is ~0.0000000172 ohm-m, aluminum ~0.0000000282 ohm-m at 20°C.

Q3: Does this account for temperature effects?
A: No, this is a basic calculation. For high-temperature environments, consult more detailed references.

Q4: Should I round up the wire size?
A: Yes, always round up to the next standard wire gauge that meets or exceeds your calculated area.

Q5: What about three-phase systems?
A: For three-phase, the calculation differs slightly (multiply by √3 instead of 2). Use a three-phase specific calculator.