Which of the following is a common type of circuit protection device?

A fuse is a common type of circuit protection device designed to protect electrical circuits from overcurrent conditions, which can lead to overheating and potential damage to the circuit or connected devices. The principle behind a fuse is relatively straightforward: it contains a metal wire or strip that melts when the current exceeds a predetermined level, interrupting the circuit and stopping the flow of electricity. This simple yet effective means of protection is critical for maintaining safety and preventing electrical fires.

In contrast, a transformer is used to change the voltage level in an AC circuit, which does not provide protection against overcurrent. A capacitor serves to store electrical energy temporarily and can be used in various applications such as filtering and smoothing out voltage variations, but it does not protect circuits against overloads. A relay, while it can control a circuit, typically plays a role in switching applications and does not inherently provide protection against overcurrents like a fuse does. Thus, the fuse stands out as the primary device for circuit protection in this context.