Red Seal Electrician Practice
Motor controlsQuestion 254 of 1506

A solid-state relay has no mechanical contacts. What does it use to switch the load?

  1. A mercury tube in a glass body
  2. An SCR, TRIAC or transistor
  3. A reed switch in a glass capsule
  4. A spring-loaded armature with pads
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Correct answer: An SCR, TRIAC or transistor

These semiconductor devices replace the mechanical contacts, and they are optically coupled to the input LED.

Source: Lessons in Electric Circuits IV: Digital (Kuphaldt), 5.5: Solid-state Relays

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Questions last reviewed: 18 October 2026