Where should a fuse or circuit breaker be installed in a 120V AC power circuit?
The correct answer is A: In series with the hot conductor only. A fuse or circuit breaker should be installed in series with the hot conductor only in a 120V AC power circuit. The hot conductor is the ungrounded conductor that can shock you, so it's the one that needs protection. The neutral is grounded and doesn't need a fuse. For amateur radio operators, understanding proper fuse placement is essential for safe electrical installations. Fuses protect against overcurrent in the hot conductor.
Exam Tip
Fuse = in series with hot conductor only. Think 'F'use = 'F'ollows 'H'ot conductor in series. Protects against overcurrent. Never fuse neutral - creates shock hazard. Must be in series, not parallel.
Memory Aid
"Fuse = in series with hot conductor only. Think 'F'use = 'F'ollows 'H'ot in series. Protects against overcurrent in the ungrounded (hot) conductor. Never fuse neutral."
Real-World Application
You're wiring a 120V circuit. The fuse goes in series with the black (hot) wire only. Current flows: hot wire → fuse → load → neutral. If overcurrent occurs, the fuse in the hot wire opens, stopping all current. Fusing the neutral would be dangerous because the circuit could appear off while the hot wire is still live.
Key Concepts
Why Other Options Are Wrong
Option B: Incorrect. Fusing the neutral is wrong and dangerous - if the neutral fuse blows, the circuit appears off but the hot conductor is still live, creating a shock hazard.
Option C: Incorrect. Fuses must be in series (part of the current path), not in parallel. Parallel connection would short-circuit the circuit.
Option D: Incorrect. Fuses must be in series, not parallel, and only on the hot conductor, not both conductors.
题目解析
The correct answer is A: In series with the hot conductor only. A fuse or circuit breaker should be installed in series with the hot conductor only in a 120V AC power circuit. The hot conductor is the ungrounded conductor that can shock you, so it's the one that needs protection. The neutral is grounded and doesn't need a fuse. For amateur radio operators, understanding proper fuse placement is essential for safe electrical installations. Fuses protect against overcurrent in the hot conductor.
考试技巧
Fuse = in series with hot conductor only. Think 'F'use = 'F'ollows 'H'ot conductor in series. Protects against overcurrent. Never fuse neutral - creates shock hazard. Must be in series, not parallel.
记忆口诀
Fuse = in series with hot conductor only. Think 'F'use = 'F'ollows 'H'ot in series. Protects against overcurrent in the ungrounded (hot) conductor. Never fuse neutral.
实际应用示例
You're wiring a 120V circuit. The fuse goes in series with the black (hot) wire only. Current flows: hot wire → fuse → load → neutral. If overcurrent occurs, the fuse in the hot wire opens, stopping all current. Fusing the neutral would be dangerous because the circuit could appear off while the hot wire is still live.
错误选项分析
Option B: Incorrect. Fusing the neutral is wrong and dangerous - if the neutral fuse blows, the circuit appears off but the hot conductor is still live, creating a shock hazard. Option C: Incorrect. Fuses must be in series (part of the current path), not in parallel. Parallel connection would short-circuit the circuit. Option D: Incorrect. Fuses must be in series, not parallel, and only on the hot conductor, not both conductors.
知识点
Fuse placement, AC circuits, Hot conductor, Electrical safety
Verified Content
Question from official FCC Technician Class question pool. Explanation reviewed by licensed amateur radio operators.