Breakdown, also called puncture, is a disruptive electrical discharge that happens when insulation can no longer withstand the applied voltage.
In cable systems, breakdown is the failure point of insulation when its dielectric strength is exceeded. At this stage, electricity arcs through the insulation, creating a direct path between the conductor and external surfaces. This puncture compromises safety, leading to overheating, system failure, or equipment damage. Factors that influence breakdown include insulation thickness, material quality, defects, and environmental stressors such as heat, moisture, or chemicals. Manufacturers use breakdown voltage testing to identify the maximum voltage insulation can resist before failure, ensuring safe operation and compliance with industry standards.
Insulation breakdown performance is tested and defined by UL (Underwriters Laboratories), ASTM (American Society for Testing and Materials), IEC (International Electrotechnical Commission), and IEEE (Institute of Electrical and Electronics Engineers).
The study of insulation breakdown grew in importance with the expansion of high-voltage power distribution in the late 19th and early 20th centuries. Engineers developed dielectric strength testing to measure material limits, a practice that remains central to modern cable design and certification.