If an MCB protects from overcurrent, which device protects from overvoltage?
Over-voltage protection is mostly provided in the design of the generation, transmission and distribution system. There are over-voltage, under-voltage, phase-loss, frequency deviation and other protections provided at the substation level. Large industrial facilities may have such protections at the utilization level, but they essentially have their own substations and may be serviced by more than one transmission line. Residential, commercial and most residential installations depend on the utility to provide that protection. Some facilities with emergency power generation have such protections.

The protection devices are generally called protection relays. Protection relays may interrupt power through the use of shunt-trip or motor-operated circuit breakers. The overall design of power distribution protection systems is an extensive area of study.