Define puncture voltage.

• A. The voltage at which the insulator glows.
• B. The voltage at which dielectric breakdown occurs through the material or internal paths during testing.
• C. The voltage at which the insulator melts completely.
• D. The voltage at which surface leakage becomes visible.

Answer: (B)

Puncture voltage is the voltage level at which the insulating material loses its dielectric strength and a breakdown path forms through the thickness of the insulator during a test. It marks the point where current can flow through the body of the insulation, rather than along its surface. This is different from surface leakage (which occurs along the surface) and from melting (which is a thermal failure). In a puncture test, the voltage is elevated until a through-insulation breakdown occurs, and that voltage value is the puncture voltage.