Red Seal Electrician Practice
Motor controlsQuestion 21 of 1506

A fire alarm is redesigned with normally closed switches in series feeding a relay that keeps the siren off. A wire in the switch string breaks. What happens?

  1. The relay drops out and the siren sounds as a fault warning
  2. The siren stays silent, but the control relay overheats until it burns out
  3. Only the switch on the broken wire stops working, while the others still work
  4. The siren turns off if it was already sounding, and the relay stays latched
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Correct answer: The relay drops out and the siren sounds as a fault warning

A break acts like a pressed switch, so the failure shows up as a false alarm. This is fail-safe design.

Source: Lessons in Electric Circuits IV: Digital (Kuphaldt), 6.5: Fail-safe Design

Practice motor controls

Questions last reviewed: 18 October 2026