The ER 100ims type protection is used to control isolation status in isolated low-voltage electrical networks. Depending on the method of connecting the protection to the controlled network, it may perform the following functions:

• Central-interlocking leakage safety device of the three-phase alternating voltage network. In this case, three ED 100i chokes connected at one end to the three phases of the network and at the other end connected at one point to form the “artificial zero” system to which the ER 100ims measuring relay of the protection is connected,
• Central-interlocking leakage safety device of the single-phase alternating voltage network. In this case, two ED 100i chokes connected at one end to the phases conductors of the network and at the other end connected at one point to which the ER 100ims measuring relay of the protection is connected,
• Blocking leakage protection of the three-phase and single-phase alternating voltage networks,

Measurement circuit of the measuring relay ER 100ims can only operate with the controlled network via the ED 100i, ED 100i.2p or ED 100i.3p chokes.

The following functions are fulfilled in these applications:

• Signalling and/or tripping when the insulation condition falls below the set reference value, the controlled release time relay is released, whose contacts signal tripping and/or disconnects a circuit breaker or a contactor,
• Measurement and indication of insulation condition, where an intrinsically safe analogue output can be connected to an intrinsically safe voltage indicator (0÷10V) scaled to the reading of insulation resistance, e.g. ER 100ws and/or an intrinsically safe voltage converter to another analogue signal to transmit this information to other control and monitoring systems,

The non-intrinsically safe circuit consists of contacts and relay coil as well as power supply for the protection. The analogue output can be connected to intrinsically safe circuits of the ia rated protection (e.g. ER 100ws or to an intrinsically safe signal separator), and its measuring circuit sends an intrinsically safe signal ia through a system of ED 100i chokes to the controlled network.

The device in the front part is equipped with a switch to select whether the tripping status after the occurrence of earth fault is to be reset manually or automatically.