Where should a fuse or circuit breaker be installed in a 120V AC power circuit?

In a standard 120V AC power circuit, the 'hot' wire carries the voltage relative to ground, while the 'neutral' wire is tied to ground at the main service panel. A fuse or circuit breaker must be installed in series with the hot conductor to safely disconnect the voltage source when an overcurrent event occurs. If the fuse were placed in the neutral wire instead, a blown fuse would stop the device from functioning, but the internal circuitry would still be fully energized with 120 volts from the unbroken hot wire. This creates a severe and hidden shock hazard for anyone opening the equipment. Fuses must always be installed in series, never in parallel. A parallel installation would simply cause a direct short circuit across the power lines the moment the device was plugged in.