A visible sign that a porcelain insulator has flashed over is?

A visible white-glaze burn is a key indicator that a porcelain insulator has experienced a flashover. This occurrence happens when electrical current arcs over the surface of the insulator, leading to localized heating that causes the porcelain to generate a distinctive burn mark. The white-glaze burn signifies that the insulator has been subjected to high-voltage conditions that resulted in the breakdown of its insulating properties, affecting its functionality.

In contrast, while a failure of the attachment point, melting of the ball joint, and cracks on the top side of the insulator may indicate other types of stress or damage, they do not specifically denote that a flashover has occurred. The visible white-glaze burn is uniquely tied to the phenomenon of flashover, making it the most accurate choice in this context. Understanding this helps in both identifying insulator failures and ensuring the reliability of electrical systems.