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  • Insulation monitoring device for AC and DC IT systems
  • Application control circuits
  • According to IEC 61557-8
  • Two separately configurable response values
  • Multi-functional LC display

The ISOMETER® of the IR425 series is designed to 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-energized systems to be monitored too.


  • 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)


  • 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

ISOMETER® IR425-D4 Variant(s)

TypeNominal system voltage* UnSupply voltage* USResponse value RanSystem leakage capacitance CeArt. No.**
IR425-D4-1DC/AC 0…300 V,
15…460 Hz
DC 9,6…94 V/
AC 16…72 V, 15…460 Hz
1…200 kΩ< 20 µFB71036403
IR425-D4-2DC/AC 0…300 V,
15…460 Hz
DC 70…300 V/
AC 70…300 V, 15…460 Hz
1…200 kΩ< 20 µFB71036402

* Absolute values
**(B7… = push-wire terminal / B9… = screw-type terminal)

Optional Accessories for ISOMETER® IR425-D4

TypeArt. No.
Mounting clip for screw mounting (one piece per device)B98060008
Mounting frame XM420B990994 

Downloads for ISOMETER® IR425-D4

Declarations of Conformity IR42x - UKCA 140.6 KB 2022/12/20 05:59:3520.12.2022 05:59:35
CE Declarations of conformity IR42x 94.2 KB 2022/08/12 06:17:2412.08.2022 06:17:24
Manuals IR425-D4 1.1 MB DE2019/05/13 10:31:4113.05.2019 10:31:41D00039
Manuals IR425-D4 1.1 MB EN2019/05/13 10:31:4113.05.2019 10:31:41D00039
Manuals IR425-D4 932.3 KB ES2019/05/13 10:31:5413.05.2019 10:31:54D00039
Manuals IR425-D4 385.4 KB IT2019/05/13 10:31:5513.05.2019 10:31:55D00039
Datasheets IR425-D4 323.8 KB DE2019/05/13 10:31:3413.05.2019 10:31:34D00039
Datasheets IR425-D4 276.8 KB EN2019/05/13 10:31:3613.05.2019 10:31:36D00039
Datasheets IR425-D4 314.2 KB ES2019/05/13 10:31:3713.05.2019 10:31:37D00039
Datasheets IR425-D4 452.6 KB ZH2019/05/13 10:31:3313.05.2019 10:31:33D00039
Datasheets XM420-Schnittstellenoptionen 264.1 KB DE2019/05/13 10:31:3513.05.2019 10:31:35
Datasheets XM420 interface options 223.5 KB EN2019/05/13 10:31:3613.05.2019 10:31:36D00051
Manuals IR425-D4 1.2 MB FR2019/05/13 10:31:5413.05.2019 10:31:54D00039
Technical information Changed variants of relays from goldplated to silver-plated contacts 166.3 KB EN2022/06/27 09:03:0827.06.2022 09:03:08
Technical information Geänderte Relaisvarianten von vergoldeten Kontakten auf versilberte Kontakte 166.3 KB DE2022/06/27 09:03:0827.06.2022 09:03:08