What type of test determines the voltage at which insulation between conductors fails?

• A. Dielectric Withstanding Test
• B. Insulation Resistance Test
• C. Continuity Test
• D. Dielectric Breakdown Test

Answer: (D)

The key idea is dielectric strength: you’re looking for the voltage level at which insulation between conductors stops acting as an insulator and begins to conduct, i.e., breaks down. A dielectric breakdown test does exactly that. In this test, voltage is gradually increased across the insulation while monitoring the current. As the voltage nears the material’s strength, the insulation can no longer resist the electric field, a conductive path forms, and current surges. The voltage at which this breakdown occurs is the dielectric strength of the insulation—the maximum voltage the material can safely withstand before failing.

This is different from the dielectric withstanding (hipot) test, which applies a high voltage for a set period to ensure the insulation can endure service-like stress without failing, but doesn’t necessarily identify the exact breakdown voltage. The insulation resistance test measures leakage current at a lower test voltage to gauge cleanliness and integrity, not the breakdown threshold. The continuity test checks whether a conductor path is complete, not insulation performance.