BENDER IR425-D4-1

The ISOMETER®s of the IR425 series monitor the insulation resistance of unearthed AC/DC 

control circuits (IT systems) 0…300 V. DC components existing in AC/DC systems do not 

influence the operating characteristics. An external supply voltage allows de-energised 

systems to be monitored too.

Application

• AC/DC control circuits in the industrial sector, mechanical engineering, power plants, 

elevators, automation systems etc.

• AC/DC control and auxiliary circuits in accordance with DIN EN 60204-1 

“Electrical equipment of machines”, IEC 60204-1, EN 60204-1

• AC/DC auxiliary circuits in accordance with DIN VDE 0100-725 (VDE 0100-725)

• Smaller AC/DC IT systems such as lighting systems

• Insulation monitoring for AC/DC control 

circuits 0…300 V

• Two separately adjustable response values

• Preset function 

(automatic setting of basic parameters)

• Connection monitoring system/earth

• LEDs: Power On, Alarm 1, Alarm 2

• Internal/external test/reset button

• Two separate alarm relays 

(one changeover contact each)

• N/O or N/C operation, selectable

• Fault memory behaviour, selectable

• Self monitoring with automatic alarm

• Multi-functional LC display

• Adjustable response delay

• Two-module enclosure (36 mm)

• Push-wire terminal 

(two terminals per connection)

Product description

The ISOMETER®s of the IR425 series monitor the insulation resistance of unearthed AC/DC 

control circuits (IT systems) 0…300 V. DC components existing in AC/DC systems do not 

influence the operating characteristics. An external supply voltage allows de-energised 

systems to be monitored too.

Application

• AC/DC control circuits in the industrial sector, mechanical engineering, power plants, 

elevators, automation systems etc.

• AC/DC control and auxiliary circuits in accordance with DIN EN 60204-1 

“Electrical equipment of machines”, IEC 60204-1, EN 60204-1

• AC/DC auxiliary circuits in accordance with DIN VDE 0100-725 (VDE 0100-725)

• Smaller AC/DC IT systems such as lighting systems

Function

The currently measured insulation resistance is indicated on the LC display. In this way 

any changes, for example when circuits are connected to the system, can be recognised 

easily. When the value falls below the preset response values, the response delay “ton” 

starts. Once the response delay “ton” has elapsed, the alarm relays “K1/K2” switch and the 

alarm LEDs “AL1/AL2” light up. Two separately adjustable response values/alarm relays 

allow a distinction to be made between prewarning and alarm. If the insulation resistance 

exceeds the release value (response value plus hysteresis), the alarm relays return to their 

initial position. Insulation faults are distinguished according to AC and DC faults (indication ±). 

In the event of insulation faults on the plus or minus conductor, the corresponding +/- symbol is 

activated on the display. If the fault memory is enabled, the alarm relays remain in the 

alarm state until the reset button is pressed or until the supply voltage is switched off. 

The device function can be tested using the test button. The parameterisation of the device 

can be carried out via the LC display or the function keys integrated in the front plate.

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