Which device is used to open and close a circuit automatically in response to overcurrent?

A circuit breaker is designed to open and close a circuit automatically in response to conditions such as overcurrent. Its primary function is to protect an electrical circuit by interrupting the flow of electricity when it detects an overload or a short circuit, thus preventing damage to equipment and reducing the risk of fire or electrical hazards.

When the current exceeds a predetermined limit, the circuit breaker trips, effectively breaking the circuit and stopping the flow of electricity. This resettable nature allows it to be restored to its normal operation without needing to replace a component, unlike a fuse, which must be replaced after it blows. This capability makes circuit breakers a crucial safety device in electrical systems, ensuring reliable and efficient operation while protecting both the infrastructure and users.

In contrast, fuses serve a similar protective purpose but operate by melting a wire within them when an overload occurs, requiring replacement after a fault. Switches simply control the flow of electricity manually, and transformers are used to change voltage levels without controlling current flow directly.