Motor Wire Sizing Calculator

Wire Size Formula:

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

Current (I):

amps

Length (L):

feet

Correction Factor (K):

Voltage Drop (V_drop):

volts

Conductivity (σ):

Ω⁻¹·mm²/m

Wire Size (A_w): mm²

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1. What is a Motor Wire Sizing Calculator?

Definition: This calculator determines the appropriate wire size for electric motors based on current, wire length, and electrical properties.

Purpose: It helps electricians and engineers select the correct wire gauge to ensure safe and efficient motor operation.

2. How Does the Calculator Work?

The calculator uses the formula:

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

Where:

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

Explanation: The formula calculates the minimum wire size needed to limit voltage drop to acceptable levels for proper motor operation.

3. Importance of Proper Wire Sizing

Details: Correct wire sizing prevents excessive voltage drop, overheating, and ensures motor efficiency and longevity.

4. Using the Calculator

Tips: Enter motor current, wire length, correction factor (default 1.25), maximum voltage drop (default 3V), and conductivity (default 58 for copper). All values must be > 0.

5. Frequently Asked Questions (FAQ)

Q1: Why is voltage drop important?
A: Excessive voltage drop can cause motors to run hotter, lose torque, and operate inefficiently.

Q2: What's a typical voltage drop allowance?
A: 3% of circuit voltage is common (3V for 120V circuits, 6V for 240V).

Q3: When would I change the correction factor?
A: Adjust for temperature (higher for hot environments) or for aluminum wires (use 0.61 instead of 1.25).

Q4: How do I convert mm² to AWG?
A: Use a wire gauge chart to find the nearest standard AWG size equal to or larger than the calculated mm².

Q5: Does this account for startup current?
A: No, for motors consider using 125% of full load current to account for startup surges.