Red Seal Electrician Practice
Wiring and componentsQuestion 65 of 1506

A contact is rated for a given current. Why is the same contact worn more by switching DC than by switching AC?

  1. A DC arc does not die out, but an AC arc passes through zero
  2. DC has a higher voltage than AC at the same rating, so it arcs more
  3. AC arcs are hotter and shorter than DC arcs, so they wear the contacts more
  4. DC is switched only at slower speeds, which lets the arc grow longer
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Correct answer: A DC arc does not die out, but an AC arc passes through zero

At 60 Hz, the current stops 120 times per second, which helps the arc go out.

Source: Lessons in Electric Circuits IV: Digital (Kuphaldt), 4.2: Switch Contact Design

Practice wiring and components

Questions last reviewed: 18 October 2026