What type of electrical device isolates line voltage from ground in case of a fault?

The device that isolates line voltage from ground in the event of a fault is the valve-type arrester. This type of arrester is specifically designed to protect electrical equipment by diverting excess voltage caused by surges, such as lightning strikes or switching operations. When a fault occurs, the valve-type arrester allows the surge of electricity to flow to the ground, effectively isolating the line voltage from the system. This helps to prevent damage to sensitive equipment and maintains system integrity.

In contrast, circuit breakers and fuses are protective devices used to interrupt current flow in overload or short-circuit conditions, but they do not specifically serve to isolate line voltage from ground during transient conditions. Relays are control devices that can automatically operate breakers or fuses but do not themselves isolate voltage from ground. Therefore, while they all play a role in protecting electrical systems, the valve-type arrester is uniquely designed for managing voltage surges and providing isolation in the event of a fault.