What is the main function of a relay?

A relay's primary function is to act as an electrically operated switch. It allows a low-power circuit to control a high-power circuit without any direct electrical connection between the two. This is accomplished through an electromagnetic coil that, when energized, creates a magnetic field that moves a switch arm to either complete or break a circuit.

Relays are used in a variety of applications, including automation systems, motor controls, and safety devices, enabling control of large electrical loads with a small control signal, which enhances safety and reliability in electrical systems. This function is critical in many electrical designs, especially where safety or isolation is a concern.

The other options relate to different functions in electrical systems: measuring voltage pertains to voltmeters, serving as a fuse is related to overcurrent protection, and providing insulation involves materials that prevent electrical conduction. None of these functions align with the primary role of a relay in circuit operation.