Which component is essential for protecting circuits from overloads?

A fuse or circuit breaker is essential for protecting circuits from overloads because these devices are specifically designed to interrupt the flow of electricity when the current exceeds a certain threshold. This interruption helps prevent overheating and potential fire hazards that can occur when circuits are overloaded.

Fuses operate by melting a metal wire when the current exceeds the safe limit, effectively breaking the circuit. Circuit breakers perform a similar function, but instead of melting, they automatically trip to open the circuit and can be reset once the fault is cleared. These safety features are crucial for maintaining the integrity of electrical systems and protecting both equipment and users.

The other options do not serve this protective role. A switch is used to control the flow of electricity but does not inherently provide protection against overloads. A capacitor is mainly used to store energy and smooth out electrical signals, while a rheostat is used to control resistance and current flow but does not offer protection against overloads.