What is the purpose of a fuse or circuit breaker in an electrical system?

A FUSE or CIRCUIT BREAKER protects the circuit by INTERRUPTING current flow if it exceeds a safe level — preventing overheating, damage, and fire. ASVAB Electronics Information tests safety devices. A FUSE contains a thin wire that melts (blowing) when current is too high, breaking the circuit (one-time, must be replaced); a CIRCUIT BREAKER trips and can be reset. Both prevent dangerous overcurrent (from shorts or overloads). They're rated for a specific current (amps). Knowing fuses/breakers protect against overcurrent (preventing fire) is commonly tested.