The HRN-3 Monitoring Relay is used to monitor the voltage level in single-phase systems. The monitored voltage is also the supply voltage. With the relay it is possible to set 2 independent levels. The HRN-35 variant uses a separate relay for each level, which is switched off in the normal state. In case of exceeding the upper level (e.g. overvoltage) the first relay switches on, in case of falling below the lower level (e.g. undervoltage) the second relay switches on. However, it is still possible to clearly identify the fault state. In order to avoid short-term peaks, there is a delay that can be set in the range 0-10s. This comes into effect when the device changes from the normal state to the fault state and avoids unnecessary flickering of the output relays. When resetting to the normal state, the delay is no longer effective, but the hysteresis (2-6% depending on the set voltage) is. Through the change-over contacts, further configurations and functions result depending on the current requirements of the application.