Here's why:

* Color Coding: Electrical wires are color-coded for safety. The hot wire (the one carrying the electrical current) is usually red or black.

* Symbol Meaning: The circle represents a wire, and the diagonal line indicates that it is "live" or carrying current.

Important Note: While the red circle with a diagonal line is a common symbol for a hot wire, specific symbols may vary depending on the industry and the specific application.