The Siemens Insulation monitoring relays are used for monitoring the insulation resistance between ungrounded 1- or 3-phase AC supplies and a protective conductor. They measure insulation resistances between system cables and system ground. If the value falls below the threshold value, the output relays are switched to fault status. With these devices, which are suitable for both AC and DC networks, a pulsed test signal is fed into the network to be monitored and the isolation resistance is determined. The pulsed test signal changes its form according to insulation resistance and network loss capacitance. The changed form is used to predict the changed insulation resistance.

Monitoring of setting errors
Safety in use thanks to integrated system test after start-up
Option of resetting and testing
New predictive measurement principle allows very fast response times