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.

Product Details


  • Undervoltage, overvoltage and frequency monitoring in 3(N)AC systems 70…500/288 V
  • Without external supply voltage
  • Integrated energy backup
  • Asymmetry, phase failure and phase sequence monitoring
  • Various 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 setting of basic parameters)
  • 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 setting
  • Sealable transparent cover
  • Two-module enclosure (36 mm)
  • Push-wire terminal (two terminals per connection)
  • RoHS compliant


  • Monitoring of voltage-sensitive machines and electrical installations
  • Switching machinery and equipment on and off at a certain voltage level
  • Monitoring of stand-by and emergency supply systems
  • Supply voltage monitoring of portable loads
  • Protection of three-phase motors against phase failure and phase open-circuit
  • Transformer protection, asymmetrical load can be recognised