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  • Undervoltage, overvoltage and frequency monitoring in 3(N)AC systems 0…500 V
  • Various monitoring functions selectable < U, > U, < f, > f
  • Asymmetry, phase failure and phase sequence monitoring
  • Adjustable start-up delay, response delay and delay on release

The multi-functional VMD420 series voltage relay is designed to monitor the frequency, undervoltage and overvoltage and the voltage between two threshold values in 3(N)AC systems. The voltages are measured as r.m.s. values. The currently measured value is continuously shown on the LC display. The measured value required to trigger the alarm relay is stored. Due to adjustable response times, installation-specific characteristics, such as device-specific start-up procedures, short-time voltage fluctuations, etc. can be considered. The devices require an external supply voltage.


  • Undervoltage, overvoltage and frequency monitoring in 3(N)AC systems 0…500 V
  • Asymmetry, phase failure and phase sequence monitoring
  • 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)
  • 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/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)
  • Indication of the system frequency
  • RoHS-compliant


  • Monitoring of voltage-sensitive machines and electrical installations
  • Switching on and switching 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
  • Transformer protection, asymmetrical load can be recognized

Downloads for LINETRAXX® VMD420

CE Declarations of Conformity VMx42x 93.7 KB 2022/11/04 09:31:2004.11.2022 09:31:20
Manuals VMD420 5.7 MB EN2022/06/09 10:48:1209.06.2022 10:48:12D00137
Datasheets VMD420 372.2 KB EN2022/08/10 05:51:4410.08.2022 05:51:44D00137
Quickstarts VMD420 998.0 KB EN2022/06/09 10:52:1309.06.2022 10:52:13D00137
Datasheets XM420 interface options 223.5 KB EN2019/05/13 10:31:3613.05.2019 10:31:36D00051
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

Optional Accessories for LINETRAXX® VMD420

TypeArt No.
Mounting clip for screw fixing (1 piece per device)B98060008

LINETRAXX® VMD420 Variants

TypeSupply voltage US*Nominal system voltage Un*Art. No.**
VMD420-D-1AC 16…72 V / DC 9,6…94 V, 15…460 Hz3(N)AC 0…500 V / 288 V 15…460 HzB73010005
VMD420-D-2AC/DC 70…300 V, 15…460 Hz3(N)AC 0…500 V / 288 V, 15…460 HzB73010006

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