Wire Size Calculation Formula

Wire Size Formula:

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

Length (L):

Current (I):

Resistivity (ρ):

ohm m

Voltage Drop (Vd):

Wire Cross-Sectional Area (A):

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1. What is the Wire Size Calculation Formula?

The wire size calculation formula determines the minimum cross-sectional area of a conductor needed to limit voltage drop in an electrical circuit. It ensures proper electrical performance and safety by accounting for current, distance, material properties, and acceptable voltage drop.

2. How Does the Calculator Work?

The calculator uses the wire size formula:

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

Where:

\( A \) — Wire cross-sectional area (mm²)
\( L \) — Length of the wire (m)
\( I \) — Current flowing through the wire (A)
\( \rho \) — Resistivity of the wire material (ohm m)
\( Vd \) — Maximum allowable voltage drop (V)

Explanation: The formula calculates the minimum wire size needed to maintain voltage within acceptable limits over a given distance for a specific current load and material.

3. Importance of Wire Size Calculation

Details: Proper wire sizing is crucial for electrical safety, preventing overheating, ensuring efficient power transmission, and maintaining equipment performance by limiting voltage drop to acceptable levels.

4. Using the Calculator

Tips: Enter wire length in meters, current in amperes, material resistivity in ohm meters (copper: ~1.72×10⁻⁸), and maximum allowable voltage drop in volts. All values must be positive numbers.

5. Frequently Asked Questions (FAQ)

Q1: Why is the factor 2 included in the formula?
A: The factor 2 accounts for the round-trip length of the circuit (both positive and negative/neutral conductors).

Q2: What is typical resistivity for copper wire?
A: Copper has a resistivity of approximately 1.72×10⁻⁸ ohm meters at 20°C.

Q3: What is an acceptable voltage drop?
A: Generally, voltage drop should not exceed 3% for branch circuits and 5% for feeder circuits according to electrical codes.

Q4: Does temperature affect the calculation?
A: Yes, resistivity changes with temperature. The calculation assumes a standard temperature (usually 20°C).

Q5: How do I convert mm² to AWG?
A: Use standard conversion tables to translate the calculated cross-sectional area to American Wire Gauge (AWG) size.