Voltage monitoring relay 3-phase Monitoring relays protect expensive electrical equipment from damage caused by changes in electrical control values in the power grid and from the indirect effects of voltage changes. For example, cold rooms are equipped with compressors that are powered by electric motors. These devices cannot withstand operational disruptions, as this would cause the coolant to burn in the compressor and damage the refrigeration equipment. In the event of a disruption, the relay monitoring the network can simultaneously start up a backup power generator, for example. Phase and current monitoring relays also protect loads during long start-ups or if the motor rotor jams and there is a risk that the resulting overload will damage the equipment. Current limiting relays protect circuits from overload in order to optimize cables and connections.