Which of the following can be used for protection of electrical circuit overcurrent?

Using a fuse or circuit breaker for the protection of an electrical circuit from overcurrent is essential in ensuring safety and preventing damage. A fuse is designed to melt and break the circuit if the current exceeds a certain threshold, thereby stopping the flow of electricity before it can cause overheating or damage to wiring and other components.

Similarly, a circuit breaker serves a comparable function; it automatically interrupts the circuit when it detects an overload or short circuit, allowing it to be reset once the issue is resolved. Both devices are specifically engineered for the purpose of overcurrent protection, making them vital components in electrical systems.

In contrast, a standard switch is primarily used to control the flow of electricity in a circuit, not to protect it. A voltage regulator is designed to maintain a steady voltage level within a system, rather than to safeguard against excessive current. An isolation transformer primarily serves to isolate different sections of an electrical system and does not provide overcurrent protection. Thus, the option referring to the fuse or circuit breaker is the most appropriate for overcurrent protection.