Insulation fault location in coupled systems

ISOMETER® iso685-D-P insulation monitoring device with EDS44x insulation fault locator and IOM441 input/output module

With the ISOMETER® iso685-D-P, Bender is providing an innovative range of insulation monitoring devices which comply with state-of-the-art technology in terms of reliability, measuring methods, usability and design. In addition to performing the central function of continuously monitoring a system’s insulation to earth, the iso685 version of the range offers many additional features which can help increase the level of safety even further, and save costs.

Insulation monitoring and insulation fault location

The larger the unearthed system (IT system) to be monitored, the more difficult it is to locate possible insulation faults. With the aid of automatic insulation fault location systems, precisely this challenge can be addressed while the system is in operation. As a result, system availability is considerably increased while downtimes are minimized. Additional electrical components are required for insulation fault location systems.

The iso685-D-P version of theiso685 seriescan be used for systems with insulation fault location. A built-in locating current generator creates a limited locating current to earth when an insulation fault occurs. This locating current can be variably adjusted. With insulation fault locators from the ISOSCAN® series, this locating current can be assigned to a defective load using a measuring current transformer. The iso685-D-P communicates with the EDS440 and EDS441 insulation fault locators via an RS-485 sensor bus or top-hat rail bus. All settings for the EDS44x devices can be operated and configured via the iso685-D-P web server. It is possible to configure the parameters for each channel separately or all channels at the same time. 

… in coupled systems

The iso685-D-P insulation monitoring device can also be used in applications with coupled systems. Thanks to the EDSsync function, all iso685-D-P devices in a group and consequently also all EDS devices connected to it participate in the insulation fault location. This function is independent of whether the insulation monitoring in the coupled systems is performed via ISOnet or by the disabling of a digital input.

Insulation fault location in coupled systems

EDSsync function

With the ISOnet function, in the example illustrated above, both iso685-D-P devices measure alternately one after the other, completely irrespectively of whether the coupling switch between the systems is closed or open. There is no need for elaborate wiring of an auxiliary contact on the coupling switch. If one of the two devices detects an insulation fault, it automatically switches to insulation fault location operating mode. When the EDSsync function is activated, a search for insulation faults is performed simultaneously on both sides of the coupling switch. In large systems with several ISOnet participants, it can take several minutes for an iso685-D-P to be granted authorisation to measure, and subsequently to perform the measurement. Any device in the ISOnet group can be granted authorisation to measure and perform a manual insulation measurement, or start up manual insulation fault location, using the ISOnet priority function. In the event of a disturbance in the ISOnet system, communication errors can be assigned to a relay in order to receive a message.

ISOloop function

If the iso685-D-P device is disabled by a digital input, permanent insulation monitoring is carried out on both sides. One of the two insulation monitoring devices will only be disabled if both systems are coupled. This ensures a short insulation resistance measuring time and rapid insulation fault location in the event of a fault without a time delay.

Ring systems are regularly used aboard ships. To ensure short measuring times and rapid insulation fault location here too, disabling via a digital input is often selected. These systems have a special characteristic: the ISOloop function can be activated to ensure insulation monitoring and insulation fault location even if all coupling switches are closed. If all coupling switches are closed, one io685-D-P always remains active if the ISOloop function is activated. There is no need for an elaborate control system via a PLC. The insulation monitoring devices must simply be connected via Ethernet and have their parameters configured. This ensures that even insulation faults in loads that are only switched on briefly can be detected.

Insulation monitoring in ring systems

IOM441 input/output module

Up to 50 EDS can be connected to an iso685-D-P. By combining EDS44x with the IOM441 input/output module, a potential-free contact can be made available for each EDS44x measurement channel. This enables messages to be generated or outputs with unimportant loads  to be disconnected so that the IT system can maintain high availability for important loads.

Input/output module of the EDS44x-S with IOM441

Plain text messages simplify the search

New measuring methods also make it possible to locate high-impedance faults with high system leakage capacitances and low locating currents. The faulty channels are indicated on the display of the iso685-D-P and can be replaced by plain text messages. For example, in the event of an insulation fault on a motor, the message “Insulation fault compressor 1” could be displayed. This allows fault location without having to study a wiring diagram, further facilitating insulation fault location.


The iso685-D-P can communicate via Modbus TCP, Modbus RTU and isoData. If the iso685-D-P is used together with an EDS44x-L, communication with a higher-level control system must take place via Modbus TCP.

In DC systems, the iso685-D-P can be triggered and issue a prior warning if a DC zero sequence voltage to earth is measured. The corresponding response values for this prior warning and the shutdown can be adjusted in 5 V increments.


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