In aircraft electrical systems, automatic reset circuit breakers

Question

BlackTom AI · Accepted Answer

Automatic-reset circuit breakers are not considered acceptable primary circuit protection in aircraft because they can automatically reapply power after a fault, potentially allowing a persistent or intermittent fault to continue heating wiring or components and create a fire hazard.

Relevant concepts:
- Circuit protection in aircraft must prevent sustained overloads or faults from causing wiring or component damage and fire. 
- Circuit breakers interrupt current when an overload or short occurs; manual-reset or thermomagnetic breakers that stay open until manually reset are preferred for safety-critical systems. 
- Automatic-reset (self-resetting) breakers close again once the overload clears, which can mask intermittent faults and allow repeated energizing of a faulted circuit.

Step-by-step reasoning:
1. A fault (overload/short) causes a breaker to trip and open the circuit. With an automatic-reset breaker, when the fault current reduces (or the breaker cools), it will reclose without human intervention.
2. If the fault is intermittent or only partly cleared, the breaker may cycle repeatedly, repeatedly energizing the faulty circuit. Each cycle allows heating and stress to continue on wiring or insulation.
3. Repeated cycling increases the risk of overheating, insulation breakdown, arcing, and fire—unacceptable risks in aircraft where wiring and systems must remain reliable and safe.
4. Aviation practice therefore avoids automatic-reset breakers as the primary protection; manual reset or lockout breakers keep the circuit open until inspected and repaired.

Why the correct answer is correct:
Because of the risk of continuous re-energizing of a faulty circuit and the associated fire hazard, automatic-reset breakers should not be used as circuit protection devices in aircraft.

Why the other choices are incorrect:
- “Must be used in all circuits essential to safe operation” is false; essential circuits require reliable protection and manual intervention after a trip.  
- “Are useful where only temporary overloads are normally encountered” may describe some ground or consumer uses, but in aircraft even temporary faults can escalate; using self-resetting breakers for protection is not acceptable practice.

Conclusion: Automatic-reset circuit breakers should not be used as circuit protection devices (the provided correct answer).

In aircraft electrical systems, automatic reset circuit breakers单项选择题

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