Question T0A08
From subelement T0 - T0A
Where should a fuse or circuit breaker be installed in a 120V AC power circuit?
Why is this correct?
A fuse or circuit breaker must be installed in series with the hot conductor only because this ensures that when the overcurrent protection device operates, it disconnects the live voltage source from the circuit. Installing it in the neutral would leave the hot conductor energized, creating a shock hazard. Parallel installation (options C and D) would create a bypass path around the protective device, rendering it useless for overcurrent protection.
Memory tip
Remember the safety principle: always break the power source, not the return path. The hot conductor carries the dangerous voltage from the source, so that's what needs disconnection. Think 'hot = hazard' – protect by breaking the hazard path, not the neutral return.
Learn more
In residential and amateur radio station wiring, the hot conductor (typically black wire) connects to the source voltage at the electrical panel's main breaker. Proper overcurrent protection follows the NEC principle of interrupting the ungrounded conductor to ensure complete de-energization. This same concept applies to DC circuits where fuses protect the positive lead. Understanding this fundamental safety practice helps when designing power distribution for amateur radio equipment and ensures compliance with electrical safety standards.
Think about it
Why do you think installing a fuse in the neutral conductor would still leave a dangerous condition even though it would stop current flow when it blows?