The relay type NA11 can be used in radial networks as feeder or power transformer protection. In solidly grounded systems the residual overcurrent protection can be used on feeders of any length, while in ungrounded or Petersen coil and/or resistance grounded systems, the residual overcurrent protection can be used on feeders of small lenght in order to avoid unwanted trippings due to the capacitive current contribution of the feeder on external ground fault.
Beside to the phase and residual overcurrent protections, the automatic reclosing function is provided.

The NA11 device may be shipped with traditional CTs or with low power (LPCT) current inputs.

NA11 - Pro-n ()


Key:   standard standard optional optional alternative alternative


  • Feeder
  • Transformer

Protection functions

  • Pt100 thermometric probes (26)
  • Phase overcurrent (50/51)
  • Residual overcurrent (50N/51N)
  • Automatic reclosing (79)
  • High impedance restricted earth fault (87NHIZ)
  • Breaker failure (BF)

Monitoring and control functions

  • CB diagnostic
  • Cold Load Pickup (CLP)
  • CTs monitoring (74CT)
  • Digital Fault recording (DFR)
  • Fault and event logging (SER & SFR)
  • Logic selectivity
  • Multiple setting profiles
  • Programmable Logic Controller
  • Second harmonic restraint
  • Self-test
  • Trip circuit supervision (74TCS)


  • 2 binary inputs + 6 output relays + 8 LEDs
  • 5 binary inputs + 6 output relays + 8 LEDs
  • Auxiliary power supply 110-230 Vac/dc
  • Auxiliary power supply 24-48 Vac/dc
  • Flush, projecting, projecting, rack, with separate MMI
  • LPCT amperometric inputs
  • Network module with Ethernet FX port (optical fiber)
  • Network module with Ethernet TX port (copper RJ45) + RS485 port
  • Nominal current 1/5 A selectable by DIP-switch
  • RS485 port (unavailable with Ethernet FX port)
  • Standard CT amperometric inputs 1/5 A


  • Modbus RTU RS232 protocol
  • Modbus RTU RS485 / IEC 870-5-103 / DNP3 protocol
  • Modbus TCP/IP protocol (network board must be provided)