A brief look at the operating principle
The IMD reports deteriorating insulation; an EDS system helps identify the faulty circuit using a compatible locating current and current transformers installed on outgoing feeders.
EDS: device, system and locating current
Bender ISOSCAN® EDS devices locate insulation faults in IT systems. Bender uses “insulation fault locator” for the device and “insulation fault location system” for the complete system. They operate with a compatible locating current injector and measuring current transformers. The IMD monitors the overall system insulation resistance; the EDS helps identify the faulty outgoing circuit. The EDS designation does not imply an RCD protective function.
First the alarm, then circuit identification
When insulation resistance falls below the alarm level in an IT system, the first question is which outgoing circuit contains the fault. In a panel serving multiple loads, total resistance alone does not answer this. An EDS system complements insulation monitoring with circuit-level fault location. Fixed systems can start searching automatically; portable solutions can support maintenance investigations in existing installations or further downstream.
Locating current identifies the faulty path
A compatible generator applies a limited locating current to the system. This signal travels from the live conductors to the insulation fault and returns via PE. Measuring current transformers on the outgoing circuits detect the signal, and the EDS evaluator identifies the relevant channel. Correct mapping between channels and panel feeders makes the displayed information useful for maintenance. Under suitable system conditions, this approach allows searching during operation.
Check generator, EDS and sensor compatibility together
According to the manufacturer's description, EDS440 is used with an iso685-D-P or PGH locating current injector. Selection must therefore not assume that every IMD variant has an integrated generator. In the EDS440 example, one device evaluates multiple measuring channels and can send information to a supervisory system. Main circuits and sensitive control circuits may require different test currents and sensor specifications. Fault current limits, system capacitance, wiring and channel mapping must be verified in product documents; identical detection times or settings cannot be promised for every installation.
Fault location chain: generator, EDS and current transformer
A locating current injector, evaluator and measuring current transformer work together to identify the faulty outgoing feeder in main circuits. In the example below, iso685-D-P, EDS440 and compatible standard CTAC models perform different tasks.
ISOMETER® iso685-…-P
iso685-…-P monitors IT system insulation resistance and supports a fault location system with compatible EDS44x components. The EDS440 product page specifies iso685-D-P as a compatible locating current source.
The P variant is required; do not assume the standard iso685 has the same generator function. The S-P version is used with FP200.Explore the model and documents
ISOSCAN® EDS440
Evaluates the locating signal from iso685-D-P or a compatible PGH generator through measuring current transformers. Mapping its twelve channels to panel feeders helps identify the faulty circuit.
EDS440 is intended for main circuits; its sensor and test current selection differs from EDS441, which is intended for sensitive control circuits.Explore the model and documents
LINETRAXX® CTAC series
A compatible standard CTAC measuring current transformer converts the outgoing circuit's locating current into a signal that EDS440 can evaluate. Transformer size and conductor layout are selected for the monitored feeder.
Standard CTAC models are used with EDS440; CTAC20/01 and CTAC35/01 are specified for other evaluators such as EDS441.Explore the model and documentsThe components are not independent equivalents; generator, test current, sensor variant and channel mapping must be verified together. Product images belong to Bender.
Bender technical explanations
This English summary is based on the Bender technical sources listed below.
- Bender — Insulation fault location: The concept ↗
- Bender — ISOSCAN EDS440: functions and compatible generators ↗
Sources checked: 2026-10-22. Diagrams belong to Bender; Turkish explanations summarised by ADEO Teknik.