Wire Sizing Calculator

Proper wire sizing is critical to ensure that your electrical systems operate safely and efficiently. This calculator helps you determine the appropriate wire size based on the allowable voltage drop, system voltage, current load, distance, and wire insulation temperature rating. For more detailed guidance on wiring for campervans and van conversions, check out this comprehensive guide.

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Assumptions and Key Points

• Copper Wire: The calculator assumes that the wire material is copper, with a resistivity of 1.68 µΩ·cm (1.68 x 10-8 Ω·m).

• Temperature: The resistivity of copper increases with temperature. The calculator adjusts for temperature using a temperature coefficient of 0.00404 per °C.

• Voltage Drop: The allowable voltage drop can be selected as 3% or 10%, based on typical industry standards.

• Distance: The distance is the one-way length of the conductor. The calculator automatically doubles this distance to account for the round trip (there and back).

• Cross-Sectional Area: The calculator outputs the wire's cross-sectional area in square millimeters (mm²).

• Wire Gauge (AWG): The calculator provides the recommended American Wire Gauge (AWG) size based on the correct conversion table.

 

Formulas Used

The primary formulas used in this calculator are:

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1. Calculate Resistivity at Operating Temperature:
ρ₂ = ρ₁ × (1 + α × (t₂ - t₁))

Where:

ρ₂ = Resistivity at temperature t₂
ρ₁ = Resistivity at reference temperature t₁ (20°C)
α = Temperature coefficient of resistivity for copper (0.00404 per °C)
t₂ = Operating temperature (°C)
t₁ = Reference temperature (20°C)

 

2. Calculate Cross-Sectional Area (A):

A = (I × ρ × 2 × L) / V

 

Where:

I = Load current (Amps)
ρ = Adjusted resistivity (Ω·m)
L = Distance (one-way) in meters
V = Voltage drop (Volts)

 

3. Convert Area from Square Meters to Square Millimeters:

A_mm² = A × 1,000,000

 

Why Correct Wire Sizing Matters

Proper wire sizing prevents excessive voltage drop, which can lead to inefficiency, overheating, or even electrical fires. This calculator ensures that the selected wire size can safely carry the current over the specified distance, considering the operating temperature and voltage drop.