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

The best practice for installing a fuse or circuit breaker is to place it in series with the hot conductor only. This setup is crucial because it allows the fuse or circuit breaker to interrupt the flow of current when an overcurrent condition occurs, protecting the wiring and connected devices from potential damage or fire hazards.

When a fuse blows or a circuit breaker trips due to excessive current, it effectively breaks the circuit, stopping the flow of electricity. If the fuse or breaker were installed in series with both the hot and neutral conductors, it could complicate the circuit's operation and increase the risk of unsafe conditions.

Moreover, installing the protective device in parallel poses significant safety risks. In a parallel configuration, the protective device would not effectively interrupt the circuit in the event of a fault because current could continue to flow through the other path, leaving the circuit unprotected.

Thus, placing the fuse or circuit breaker in series with the hot conductor ensures that any overcurrent condition results in a complete interruption of power, enhancing safety for both users and equipment.