Final answer:
The two main types of overcurrent protective devices are fuses, which are one-time use devices that melt and break the circuit, and circuit breakers, which are resettable devices that trip to break the circuit.
Step-by-step explanation:
The two main types of overcurrent protective devices are fuses that melt when current reaches critical levels, and circuit breakers that trip when current reaches critical levels.
A fuse contains a metal strip with a low melting point that permanently breaks the connection of a circuit to a voltage source when overheated by excessive current. This is a one-time protection method that needs replacement after it operates. In contrast, a circuit breaker is an automatic, resettable switch. One common type uses a bimetallic strip that bends when overheated due to excessive current, triggering a mechanism that breaks the circuit connection, which can then be reset.
Both fuses and circuit breakers are essential for preventing thermal hazards by interrupting excessive currents. They act like automatic switches that open to stop current flow, hence protecting electrical systems and preventing potential electrical fires.