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The NGRM550 Neutral Grounding Resistor Monitor detects grounding-resistor failures and ground faults. It is intended for use in low-resistance grounded transformers and generators used in commercial and industrial power systems. In these systems, the NGRM550 monitors:

  • Current through the neutral-grounding resistor
  • Voltage between the star point of the transformer and ground (voltage drop across the NGR)
  • NGR failure (open), including failure of connections between neutral and ground

A benefit to many users is the multilingual user interface that allows the comfort of reading values and programming in your native language.

It is an ideal solution that is easy to retrofit into existing LRG applications or factory-install in new LRG packages. If customers prefer, they can easily program the relay via the built-in webserver.  NGRM550’s can easily connect to a supervisory system with Modbus TCP/IP or RTU communications. Capabilities extend to 25 kV and 2,000 A.


  • Determination of RNGR with passive and active measurement methods
  • Continuous monitoring of the RNGR even if the installation is de-energized
  • Alarm or trip on ground fault
  • Monitoring of the current INGR
  • Monitoring of the voltage UNGR
  • Ethernet communication
  • Webserver
  • Language selection (English, German, Spanish, French)
  • Test button (internal, external) with/without tripping
  • FFT analysis of the measuring signals
  • Relay for detection of ground faults and resistor faults
  • Relay for shutdown of the installation after a configurable time
  • Can be combined with RCMS… for automatic shutdown of feeders
  • Graphical user interface
  • Wide supply voltage range
  • Range of use up to 2,000 m AMSL
  • Fault/history memory
  • Analog output of measured values (0…10 V, 4…20 mA, etc., selectable parameters)
  • Password protection
  • Tripping on RMS, fundamental component signal or harmonics
  • Detection of AC and DC ground faults

Downloads for LINETRAXX® NGRM550

Manuals NGRM…-Modbus 443.2 KB EN2022/06/09 10:47:4409.06.2022 10:47:44D00292
Datasheets NGRM500/NGRM550 1.2 MB EN2022/06/09 10:54:4009.06.2022 10:54:40D00373
Quickstarts NGRM500/NGRM550 1.6 MB EN2022/06/09 10:52:1409.06.2022 10:52:14D00373
Manuals NGRM500/NGRM550 5.4 MB EN2022/06/09 10:48:1109.06.2022 10:48:11D00373
Technical Information NGR Checklist (US) 245.3 KB EN2022/11/07 16:39:0207.11.2022 16:39:02
Flyers NGRM550 & NGRM750 630.6 KB EN2022/05/25 06:07:5225.05.2022 06:07:52

Optional Accessories for LINETRAXX® NGRM550

Résistance de couplage CD…

TypeTension UsysRéf.
CD1000400…690 VB98039010
CD1000-2400…1000 VB98039053
CD50001000…4200 VB98039011
CD144004300…14550 VB98039054
CD2500014551…25000 VB98039055

Transformateur de courant de mesure

TypeTension / courantRéf.
W20AC jusqu'à 10 AB98080003
AC jusqu'à 25 AB98080010
CTUB103-CTBC35AC/DC bis 10 AB78120030
AC/DC jusqu'à 25 AB78120031

Tension d'alimentation pour transformateur de courant de mesure CTUB103…

TypeNombre maximal de transformateurs
de courant raccordés
STEP-PS/1 AC/24 DC/0.52B94053110
STEP-PS/1 AC/24 DC/1.757B94053111
STEP-PS/1 AC/24 DC/4.217B94053112


TypeSupply voltage US / Frequency range HzArt. No.
NGRM550AC 48…240 V, 40…70 Hz
DC 48…240 V