The voltage relays of the VME421H series are designed to monitor the frequency, undervoltage, overvoltage and the voltage between two threshold values (window discriminator function) in both AC and DC systems. The voltages are measured as r.m.s. values. The measured value is continuously shown on the device’s LC display. The measured value leading to the activation of the alarm relays will be stored. Thanks to the VMD’s to adjustable response times, installation-specific characteristics, such as time delay specific start-up procedures, short-time voltage fluctuations, etc. can be configured for specific applications. Device version VME421H takes the supply voltage from the system being monitored and utilizes an internal energy backup.


  • Voltage and frequency monitoring of single-phase machines and electrical installations
  • Earth fault monitoring in medium-voltage systems via voltage transformers
  • Monitoring of battery systems
  • Switching machinery and equipment on and off at a certain voltage level


  • Undervoltage, overvoltage and frequency monitoring of AC/DC systems, 9.6…150 V (VME421H-D-1), 70…300 V (VME421H-D-2)
  • Without external supply voltage
  • Integrated energy backup
  • Different monitoring functions selectable
    < U, > U, < f, > f
  • Start-up delay, response delay, delay on release
  • Adjustable switching hysteresis
  • r.m.s. value measurement (AC + DC)
  • Digital measured value display via multi-functional LC display
  • Preset function (automatic assignment of basic parameters)
  • LEDs: Power On, Alarm 1, Alarm 2
  • Measured value memory for operating value
  • Continuous self monitoring
  • Internal test/rest button
  • Two separate alarm relays (one changeover contact each)
  • N/C or N/O operation and fault memory behaviour selectable
  • Password protection for device setting
  • Sealable transparent cover
  • Two-module enclosure (36 mm)
  • Push-wire terminal (two terminals per connection)
  • RoHS-compliant



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