Insulation resistance (R) monitoring
In ungrounded power system, the installation must either be ungrounded or must be grounded using a sufficiently high level of impedance.
In the event of only one ground or earth fault, the fault current is very low and interruption is unnecessary. However, given that a second fault could potentially cause the circuit breaker to trip, an insulation monitoring device has to be installed to indicate an initial fault. This device must trigger an audible and/or a visual signal.
By constantly monitoring the insulation resistance, you can keep track of the system quality, which is a form of preventive maintenance.