Red Seal Electrician Practice
Wiring and componentsQuestion 581 of 1506

What does a varistor do when the voltage across it rises above its breakdown (firing) voltage?

  1. Its resistance rises sharply, and it must be replaced after one event.
  2. Its resistance stays the same, and it only changes with temperature.
  3. Its resistance drops sharply, and it is permanently damaged after one event.
  4. Its resistance drops sharply, and it is built to do this again and again.
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Correct answer: Its resistance drops sharply, and it is built to do this again and again.

A varistor has high resistance below its firing voltage and low resistance above it. Unlike a damaged insulator, it is designed to recover.

Source: Lessons in Electric Circuits I: DC (Kuphaldt), 2.6: Nonlinear Conduction

Practice wiring and components

Questions last reviewed: 18 October 2026