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Formula For Cable Size Calculation Jun 2026

To size a cable for a 100 A load current, 30 meters long, with a 3% voltage drop allowed on a 230V supply, and assuming copper conductors:

This is the most common reason for needing a larger cable. Most standards allow a maximum drop of and 5% for other loads . The Voltage Drop Formula: formula for cable size calculation

Where:

A proper cable sizing calculation follows a step-by-step algorithm, not a single plug-and-play equation: To size a cable for a 100 A

The voltage drop ((\Delta V)) in a cable can be calculated using: [ \Delta V = \fracI \cdot L \cdot (R \cdot \cos(\phi) + X \cdot \sin(\phi))1000 ] Where: 30 meters long

The Ultimate Guide to the Formula for Cable Size Calculation

The general formula for voltage drop ($V_d$) is: