Final answer:
A door-type cutout contains the main contacts, fuse, and circuit breaker within a porcelain container. Fuses break the circuit by melting a metal strip due to excessive current, while circuit breakers can be reset after breaking the circuit due to overheating.
Step-by-step explanation:
On a door-type cutout, the (a) main contacts, the fuse, and the(b) circuit breaker are housed inside a porcelain container. A fuse, as illustrated in related figures, contains a metal strip with a low melting point and is placed between two contacts. When an excessive current passes through this strip, it generates enough heat to melt the strip, permanently disrupting the electrical connection to the voltage source, thus protecting the circuit from damage. A circuit breaker functions differently than a fuse.
It acts as an automatic but restorable electric switch. One type of circuit breaker includes a bimetallic strip that bends when overheated; this action, aided by a spring, forces the metal strip to move and break the circuit connection at designated points. While a fuse must be replaced after it blows, a circuit breaker can be reset, allowing for continued use without replacement.