Red Seal Electrician Practice
Wiring and componentsQuestion 817 of 1506

How does a slow-blow fuse achieve its time delay at the same current rating?

  1. Its element has more mass, so it heats slower.
  2. Its element is longer, so it has more resistance.
  3. Its element is made of a higher-melting metal that never opens.
  4. It has a small spring that holds the contacts closed.
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Correct answer: Its element has more mass, so it heats slower.

More mass takes longer to heat, but it reaches the same final temperature for a given current, so the current rating is unchanged.

Source: Lessons in Electric Circuits I: DC (Kuphaldt), 12.4: Fuses

Practice wiring and components

Questions last reviewed: 18 October 2026