Electric Motor Wire Size Calculator (AWG)

Wire Size Formula:

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

Current (I):

Amps

Length (L):

Meters

Resistivity (ρ):

Ω·m (Copper: 1.68×10⁻⁸)

Voltage Drop (Vd):

Volts

Recommended Wire Size:

Cross-sectional Area:

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1. What is the Wire Size Calculation?

The wire size calculation determines the appropriate American Wire Gauge (AWG) for electric motor circuits based on current, length, material resistivity, and allowable voltage drop. Proper sizing ensures safe operation and prevents excessive voltage drop.

2. How Does the Calculator Work?

The calculator uses the wire size formula:

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

Where:

\( A \) — Cross-sectional area (mm²)
\( I \) — Current in amps
\( L \) — Length in meters (round-trip distance)
\( \rho \) — Resistivity of material (Ω·m)
\( Vd \) — Allowable voltage drop (volts)

Explanation: The formula calculates the minimum conductor size needed to maintain voltage drop within acceptable limits, then converts to AWG.

3. Importance of Proper Wire Sizing

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

4. Using the Calculator

Tips:

For motors, use full load current (FLA) from motor nameplate
Length should be one-way distance (calculator automatically doubles it)
Standard copper resistivity is 1.68×10⁻⁸ Ω·m
Typical voltage drop allowance is 3% of circuit voltage (3.6V for 120V, 6V for 240V)

5. Frequently Asked Questions (FAQ)

Q1: Why is wire size important for motors?
A: Motors require sufficient voltage to start and run properly. Undersized wiring causes excessive voltage drop, leading to poor performance, overheating, and reduced motor life.

Q2: What's the difference between AWG and mm²?
A: AWG is the American standard, while mm² is metric. Higher AWG numbers mean smaller wires, while higher mm² means larger wires.

Q3: When should I use aluminum instead of copper?
A: Aluminum is used for cost savings in large installations (requires larger size for same current). Use resistivity 2.65×10⁻⁸ Ω·m for aluminum.

Q4: How does temperature affect wire sizing?
A: Higher temperatures increase resistance. For hot environments, use next larger wire size or consult temperature correction factors.

Q5: What about multiple motors on one circuit?
A: Size wire for the total current of all motors plus 25% of the highest-rated motor current (NEC requirements).