What device automatically interrupts the circuit when overload conditions are detected?

A circuit breaker is a safety device specifically designed to automatically interrupt the flow of electricity in a circuit when it detects overload conditions. This function is crucial for preventing damage to the electrical system and reducing the risk of electrical fires.

When the current flowing through the circuit exceeds a predetermined limit, the circuit breaker trips, effectively opening the circuit. This action stops the flow of electricity, thereby protecting the equipment and wiring from potential overheating and damage due to excessive current.

Circuit breakers can be reset once the overload condition is resolved, allowing the circuit to be reactivated without needing to replace any components, unlike fuses, which would need to be replaced after blowing. This reset capability makes circuit breakers more convenient and reliable for modern electrical systems.

The other devices listed serve different functions: a fuse also protects circuits but must be replaced after it operates, a relay is used to control a circuit and often requires a separate control signal, and a transformer is used for changing voltage levels but does not perform any protective function.