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ISOMETER® isoLR275 with AGH-LR

  • Insulation monitoring device for AC and DC IT systems
  • Application main circuits with low-resistance insulation level
  • Separately adjustable response values 200 Ω…100 kΩ
  • Isometer disconnecting relay for the operation of several ISOMETER® in interconnected IT systems
  • History memory with real-time clock for storing alarm messages with date and time

The isoLR275 ISOMETER® in conjunction with the AGH-LR coupling device monitors the insulation resistance of IT systems. It is suitable for universal use in 3(N) AC, AC/DC and DC systems. AC systems may include extensive DC-supplied loads, such as converters or thyristor-controlled DC drives. The adaptation to the existing system leakage capacitances takes place automatically.

Only use the AGH-LR coupling device supplied with the device for adaptation of the nominal voltage range.

isoLR275 can share the BMS bus with other bus devices



  • ISOMETER® for IT AC systems with galvanically connected rectifiers or converters and for IT DC systems (IT = unearthed systems)
  • Particularly suited for monitoring electrical installations with a low level of resistance
  • isoLR275 is always operated in conjunction with AGH-LR
  • Automatic adaptation to the existing system leakage capacitance
  • AMPPlus measurement method (European Patent: EP 0 654 673 B1)
  • Choice of measurement methods to meet different requirements
  • Two separately adjustable response ranges of 0.2 kΩ…100 kΩ each (Alarm 1, Alarm 2)
  • Two-line LC display
  • Automatic device self test
  • Memory with real-time clock to store alarm messages with date and time stamp
  • BMS interface (Bender Measuring Device Interface) for communication with other Bender devices (RS-485 galvanically isolated)
  • Internal disconnection of the ISOMETER® from the IT system to be monitored (via control signal; terminals F1/F2), e.g. if several ISOMETER®s are interconnected
  • Current output 0(4…20 mA (electrically isolated) in relation to the insulation value measured in the system


  • Coupling device required for ISOMETER® isoLR275
  • Nominal voltage range AC 0…793 V and DC 0…1100 V
  • DIN rail mounting


  • AC, DC or AC/DC main circuits
  • IT systems with directly connected inverters
  • IT systems with high system leakage capacitances of up to 500 μF
  • IT systems with high but slow voltage fluctuations
  • Systems including switched-mode power supplies
  • Coupled IT systems

ISOMETER® isoLR275 with AGH-LR Variant(s)

TypeNominal system voltage UnSupply voltage USArt. No.
isoLR275-327 + AGH-LR-3

consisting of:
3(N) AC 0…793 V / DC 0…1100 VAC 19,2…55 V / DC 19,2…72 VB91065702W

isoLR275-335 + AGH-LR

consisting of:
3(N)AC 0…793 V / DC 0…1100 VAC 88…264 V / DC 77…286 VB91065703W


Downloads for ISOMETER® isoLR275 with AGH-LR

CE Declarations of conformity isoLR275 83.2 KB 2022/08/12 06:17:2512.08.2022 06:17:25
Datasheets isoLR275 391.2 KB DE2019/05/13 10:31:3513.05.2019 10:31:35D00127
Datasheets isoLR275 342.2 KB EN2019/05/13 10:31:3713.05.2019 10:31:37D00127
Datasheets isoLR275 336.8 KB ES2019/05/13 10:31:3713.05.2019 10:31:37D00127
Datasheets isoLR275 645.8 KB ZH2019/05/13 10:31:3313.05.2019 10:31:33D00127
Manuals isoLR275 2.2 MB DE2021/04/20 08:07:5120.04.2021 08:07:51D00127
Manuals isoLR275 2.1 MB EN2021/04/20 08:09:3120.04.2021 08:09:31D00127
Quickstarts isoLR275 999.5 KB DE2021/03/12 07:05:2612.03.2021 07:05:26D00127
Quickstarts isoLR275 999.5 KB EN2021/03/12 07:05:2612.03.2021 07:05:26D00127