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The CMD420/421 current monitoring devices monitor AC currents using three measuring inputs for overcurrent, undercurrent or undercurrent and overcurrent (window discriminator function). The currents are measured as r.m.s. values (AC). The currently measured values are continuously shown on the LC display. The respective measuring channel can be selected using the Arrow up or Arrow down button. The measured values causing the alarm relay to switch are stored. Due to adjustable delay times, installation-specific characteristics, such as device-specific making currents, short-time current changes etc. can be considered. For the measurement three standard current transformers are to be connected to the respective CMD420/421. The transformation ratio "n" of the current transformers (n = x/1A resp. n = x/5A) can be set up to a factor of n = 2000. Then the actual current of the installation can be calculated by multiplying the measured current by factor "n" and indicated on the display. The currents can derive from a 3-phase system or from three different single-phase systems. The CMD420/421 series requires external supply voltage


  • Undercurrent and overcurrent monitoring in AC systems with prealarm and main alarm or current monitoring with window discriminator function
  • Current monitoring using current transformers, suitable for standard transformers x/1 A, x/5 A (depending on the device type)
  • Transformation ratio n allows adaptation to all standard current transformers x/1 A, x/5 A
  • Start-up delay, response delay and delay on release
  • Adjustable switching hysteresis
  • r.m.s. value measurement AC
  • Digital measured value display via multi-functional LC display
  • LEDs: Power On, Alarm 1, Alarm 2
  • Fault memory for the operating value
  • Cyclical self monitoring
  • Internal test/reset button
  • Two separate alarm relays with 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


  • Current consumption of motors, such as pumps, elevators, cranes
  • Monitoring of lighting circuits, heating circuits, charging stations
  • Monitoring of emergency lighting
  • Monitoring of screw conveyors, e.g. in sewage plants
  • Dust removal in wood working
  • 70 % agreement in accordance with EEG 2012 for PV inverters

Downloads for LINETRAXX® CMD420/CMD421

CE Declarations of Conformity CMD42x 87.6 KB 2022/08/12 06:17:2412.08.2022 06:17:24
Manuals CMD420/421 2.8 MB EN2021/11/03 08:21:1603.11.2021 08:21:16D00101
Datasheets CMD420/421 330.2 KB EN2022/06/09 10:54:3709.06.2022 10:54:37D00101
Quickstarts CMD420/421 1.0 MB EN2021/11/03 10:53:2503.11.2021 10:53:25D00101
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® CMD420/CMD421

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

LINETRAXX® CMD420/CMD421 Variants

TypeSupply voltage US*MeasurementResponse valueArt. No.**
CMD420-D-1AC 16…72 V / DC 9,6 V…94 V, 15…460 Hzvia current transformer x/1A0,1…1 A x nB73060006
CMD420-D-2AC/DC 70…300 V 15…460 Hzvia current transformer x/1A0,1…1 A x nB73060007
CMD421-D-1AC 16…72 V / DC 9,6 V…94 V, 15…460 Hzvia current transformer x/5A0,5…5 A x nB73060008
CMD421-D-2AC/DC 70…300 V 15…460 Hzvia current transformer x/5A0,5…5 A x nB73060009

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