Voltage Drop Calculations

In 2008, I have written some articles on voltage drop calculations as a tool in the selection of the correct cable sizes.

  1. Voltage Drop Calculation;
  2. Voltage Drop Calculation Part 2;
  3. Voltage Drop Calculation Part 3;

This tutorial is an update of above-mentioned tutorials combined into single article complete with a downloadable pdf. The calculations will be based on IEC standards or its derivatives. However, the calculations will likewise be applicable to North American standards using the correct cable parameters.

The selection of cables depends on several factors

  1. Current carrying capacity of conductor with derating factors applied;
  2. Conductor operating temperature as an effect of the load current;
  3. Voltage drop during normal operation is within acceptable limits;
  4. Voltage dip during motor starting, if applicable, is within acceptable limits;
  5. Short-circuit withstand to ensure that conductor will not melt during a short-circuit condition.

Only item 4—voltage drop will be considered in this tutorial. At the end of this tutorial, the electrical engineer will be able to select the correct cable size taking into account the effect of voltage drop.

A complete version of this tutorial is available for download using this link.