Transmitters for permanent, comprehensive electricity usage monitoring

Need to know how energy on your site is used in detail? The Eltek GD90A and GD900A transmitters used with ND sub metering systems provides the solution. Analyse energy usage across large sites where power is distributed to a range of facilities and services and derive a best usage pattern.


The GD90A interfaces with the Northern Design NDRail350 (1 x 3 phase load) or NDRail310 (3 x single phase load) energy meters, providing comprehensive monitoring and patterns of use of a three phase supply. Information transmitted:

  • 3 x Current (up to 100A) phases
  • 3 x power factor
  • 1 or 3 Voltage phase
  • Calculated values transmitted or derived for: kVA, kVAr and kW

System Layout



The GD900A can be used with up to six parallel connected NDRail310 or NDRail350 energy meters and appropriate current transformers, providing comprehensive monitoring and patterns of use of multiple three phase supplies.

System Layout

GD90A / GD900A


If you require sensors, please order them separately.

Current transformer (one per phase) with 1m lead - other types available POA:
Type Range Size (mm) Cable diameter  
SCL8-5 0-5A 43 x 37 x 32
SCL16-50 0-50A 51 x 45 x 27 16mm
SCL16-100 0-100A 51 x 45 x 27 16mm
SCT19-150 0-150A 51 x 53 x17 19mm SCT closed SCT open
SCT32-400 0-400A 82.5 x 85 x 27 32mm
SCT51-800 0-800A 121 x 127 x 32 51mm
Other SCT19 models available: 5, 10, 15, 20, 30, 50, 70 and 100A - refer to Eltek
Other SCT32 models available: 70, 100, 150, 200, 250, 300, 400 and 600A
Other SCT51 models available: 600, 1000A
DRA18-12 DIN rail mounting AC to 12VDC power supply
NDRail350 DIN rail mounting energy meter
(1 x 3 phase load)

NDRail310 DIN rail mounting energy meter
(3 x 1 phase loads)

See for more information.


WBG Wall bracket docking kit

This kit enables fitment of the transmitter's built-in wall bracket to difficult or uneven surfaces. The kit provides additional docking security.

The following products are supported:

  • All GD, GC, GL and GS series transmitters
  • RP250GD repeater and RC250 receiver


Transmitter Specification

Model(s) Sensors Range
GD90A 1 x RS485 modbus input for NDRail310 or NDRail350 energy meter 3 x Current (up to 100A) phases
3 x power factor
1 or 3 Voltage phase
Calculated values transmitted or derived for: kVA, kVAr and kW
GD900A As GD90A but can connect to up to 6 x NDRail310 or 6 x NDRail350 meters  

NDRail350 Specification

Isolation: Fully isolated
Actual range: Voltage 50% to 120%, current 0.2% to 120%
Frequency range: 45 to 65Hz ( up to 30th harmonic at 50Hz)
Burden per phase: Voltage or current <0.1VA
Accuracy (voltage or current): To class 0.1 IEC60688
Max Current: Direct mode (not using CT) max current is 5A (operating under installation category II(IEC 61010-1)
Indirect mode (using appropriately rated CT) up to 1000A
Dimensions: 106 x 90 x 58mm (DIN rail mounting)
Display: All values can be viewed via built in LCD and button panel

Common GenII Transmitter Specification

RF specification: EN300-220
RF power: 10mW
Environment specification  
  Compliant to EN300-220: -10 to +55°C
  Actual: -30 to +65°C
  Humidity: 100% non condensing
Environmental rating: IP40
Dimensions (footprint): 78 x 41mm
Transmission interval range: 1 sec to 4 hours
Indicator (red LED): transmit active/on/off
Control switch (concealed): test mode / hibernate
Antenna socket: SMA


Common to all transmitters

Gen II Quick Start Instructions

Specific to this family of transmitters


Energy monitoring datasheet (GD90A)
Energy monitoring multidrop datasheet (GD90A and GD900A)

User Instructions:

GD90A User Instructions
GD900A User Instructions