Red Seal Electrician Practice
Motor controlsQuestion 24 of 1506

For the protective relay trip circuit described in the text, what is the weakness of the closed-contact trip design?

  1. The breaker trips whenever the relay is tested, which causes false outages
  2. The trip coil overheats from the constant current that the relay supplies
  3. The breaker closes by itself after the fault and sends power back to the line
  4. An open wire is silent, so the relay cannot trip the breaker
Show answer

Correct answer: An open wire is silent, so the relay cannot trip the breaker

A silent open failure shows up only when protection is needed.

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

Practice motor controls

Questions last reviewed: 18 October 2026