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  • Electrical safety for unearthed power supplies (IT systems)
  • Insulation monitoring equipment, insulation fault location systems
  • Power supplies for medical applications
  • Measuring and monitoring relays
  • Electrical safety for earthed power supplies (TN systems)
  • Using renewable energies efficiently: wind power, photovoltaics
  • Test systems for electrical equipment and medical technology


According to DIN V VDE V 0126-1-1, the voltage and frequency shall be monitored when feeding power into the public low voltage grid from private electricity generation systems > 30 kW (such as CHPs, wind power stations, hydroelectric power plants and photovoltaic systems).

The three-phase VMD423 series voltage and frequency monitors monitor the voltage and frequency at the feeding point of the public grid. At the feeding point of the medium voltage grid, the output voltages and frequencies are measured by means of voltage transformers (100 V). An alarm relay is activated within ≤ 80 ms when limit values are reached (response values according to VDEW guideline “Private electricity generation systems at the medium voltage grid”). An overvoltage (> U2), measured as average value over a 10-minute period, will cause the alarm relay to switch.

The voltages are measured as r.m.s. values. In addition asymmetry, phase failure and phase sequence are monitored. 

The VMD423 is suitable for multifunctional monitoring tasks and can be adapted to the requirements of the electricity supply companies.

The currently measured values are continuously shown on the LC display. The measured value causing the alarm relay to switch is saved. Due to adjustable start-up delay and delay on release, the network operator's specific requirements can be considered such as device-specific start-up procedures, short-time voltage fluctuations etc.

The VMD423 series requires a separate supply voltage, whereas the VMD423H version draws its supplies from the system.

Certificate of non objection in accordance with

  • DIN V VDE V 0126-1-1:2006-02 (France, Switzerland)
  • DIN V VDE V 0126-1-1:2006-02 and EN 50438:2007 (Czech Republic)
  • C10/11 (Belgium)


  • VMD423 with separate supply voltage
  • VMD423H is supplied by the system being monitored
  • Undervoltage, overvoltage and under­frequency and overfrequency monitoring in 3(N)AC systems
    AC 0…500 V
  • Monitoring of overvoltage by average determination of the latest 10-minute measuring interval
  • Asymmetry, phase failure and phase sequence monitoring
  • Start-up delay, response delay and delay on release
  • Adjustable switching hysteresis
  • r.m.s. value measurement (AC+DC)
  • Digital measured value display via multi-functional LC display
  • LEDs: Power On, Alarm 1, Alarm 2
  • Measured value memory for operating value
  • Continuous self monitoring
  • Internal test/reset button
  • Two separate alarm relays (one changeover contact each)
  • N/C or N/O operation and fault memory behaviour selectable
  • Password protection for device settings
  • Sealable transparent cover
  • Push-wire terminal (two terminals per connection)
  • Two-module enclosure (36 mm)
  • RoHS compliant


  • Monitoring of automatic switching points between private electricity generation power system in parallel operation with the public low voltage grid
  • Applications according to DIN V VDE V 0126-1-1 (VDE V 0126-1-1): 2006-02, C 10/11, EN 50438:2007
  • Universally applicable for photovoltaic systems, CHPs (Combined Heat and Power plants), wind power and hydro power plants

Downloads for LINETRAXX® VMD423/VMD423H

Declarations of Conformity Unbedenklichkeitsbescheinigung VMD423-D-(2) 89.1 KB DE13.05.2019 10:31:39D00139
Declarations of Conformity Potvrzení o nezávadnosti VMD423-D-(2) 175.8 KB CZ13.05.2019 10:31:39D00139
Declarations of Conformity Compliantiecertificaat VMD423-D-(2) 87.5 KB NL13.05.2019 10:31:39D00139
Declarations of Conformity Certificate of compliance VMD423-D-(2) 90.5 KB EN13.05.2019 10:31:39D00139
Datasheets VMD423/VMD423H 392.5 KB DE13.05.2019 10:31:35D00140
Datasheets VMD423/VMD423H 354.3 KB EN13.05.2019 10:31:36D00140
Datasheets VMD423/VMD423H 355.5 KB ES13.05.2019 10:31:37D00140
Datasheets VMD423/VMD423H 650.4 KB ZH13.05.2019 10:31:33D00140
Declarations of Conformity Dichiarazione di conformità VMD423-D-(2) 91.5 KB IT13.05.2019 10:31:39D00139
Manuals VMD423/VMD423H 5.3 MB DE29.06.2021 14:45:06D00139
Manuals VMD423/VMD423H 5.0 MB EN29.06.2021 14:07:18D00139
Quickstarts VMD423/VMD423H 906.0 KB DE02.11.2020 12:32:23D00139
Quickstarts VMD423/VMD423H 906.0 KB EN02.11.2020 12:32:23D00139
Technical information Changed variants of relays from goldplated to silver-plated contacts 166.3 KB EN27.06.2022 09:03:08
Technical information Geänderte Relaisvarianten von vergoldeten Kontakten auf versilberte Kontakte 166.3 KB DE27.06.2022 09:03:08

Optional accessories for LINETRAXX® VMD423/VMD423H

TypeArt. No.
Mounting clip for screw fixing (one clip per device)B98060008

LINETRAXX® VMD423/VMD423H Variants

TypeSupply voltage US*Nominal system voltage Un*Response valueArt. No.**
VMD423-D-1DC 9,6…94 V/
AC 16…72 V, 15…460 Hz
3(N)AC 0…500 V,
40…65 Hz
AC 10…500 VB73010020
VMD423-D-2DC 70…300 V/
AC 70…300 V, 15…460 Hz
3(N)AC 0…500 V,
40…65 Hz
AC 10…500 VB73010021
VMD423H-D-3Un3(N)AC 0…500 V,
40…65 Hz
AC 70…500 VB73010022

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