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

The ISOMETER® IR420-D4 monitors the insulation resistance of unearthed AC control circuits (IT systems) 0…300 V. If the systems to be monitored include DC components, such as switched-mode power supplies or solenoid valves, the display and operating characteristics may be affected.
The display and response values apply to pure AC systems. An external supply voltage allows de-energised systems to be monitored too.


  • Insulation monitoring for IT control circuits AC 0…300 V
  • Two separately adjustable response values
  • Preset function (automatic assignment 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 message
  • Multi-functional LC display
  • Adjustable response delay
  • Two-module enclosure (36 mm)
  • RoHS-compliant
  • Push-wire terminal (two terminals per connection)


  • AC control circuits in the industrial sector, mechanical engineering, power plants, elevators, automation systems etc.
  • AC control and auxiliary circuits in accordance with IEC 60204-1 / DIN EN 60204-1 Electrical equipment of machines
  • AC auxiliary circuits in accordance with DIN VDE 0100-725 (VDE 0100-725)
  • Smaller AC IT systems such as lighting systems, mobile generators

ISOMETER® IR420-D4 Variant(s)

TypeNominal system voltage* UnSupply voltage* USResponse value RanSystem leakage capacitance CeArt. No.**
IR420-D4-1AC 0…300 V, 42…460 HzDC 9,6…94 V /
AC 16…72 V, 42…460 Hz
1…200 kΩ< 20 µFB71016409
IR420-D4-2AC 0…300 V, 42…460 HzDC 70…300 V /
AC 70…300 V, 42…46 Hz
1…200 kΩ< 20 µFB71016405

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

Optional Accessories for ISOMETER® IR420-D4

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

Downloads for ISOMETER® IR420-D4

CE Declarations of conformity IR42x 94.2 KB 2022/08/12 06:17:2412.08.2022 06:17:24
Manuals IR420-D4 918.5 KB DE2019/05/13 10:31:4113.05.2019 10:31:41D00037
Manuals IR420-D4 918.5 KB EN2019/05/13 10:31:4113.05.2019 10:31:41D00037
Manuals IR420-D4 921.8 KB ES2019/05/13 10:31:5413.05.2019 10:31:54D00037
Manuals IR420-D4 375.0 KB FR2019/05/13 10:31:5413.05.2019 10:31:54D00037
Datasheets IR420-D4 327.3 KB DE2019/05/13 10:31:3413.05.2019 10:31:34D00037
Datasheets IR420-D4 281.3 KB EN2019/05/13 10:31:3513.05.2019 10:31:35D00037
Datasheets IR420-D4 273.6 KB ES2019/05/13 10:31:3713.05.2019 10:31:37D00037
Datasheets IR420-D4 131.1 KB ZH2019/05/13 10:31:3313.05.2019 10:31:33D00037
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