M-3420 Generator Protection System 

Please Note: As of 12/31/2022, Beckwith Electric will no longer be manufacturing the M-3420 Generator Protection System.

  • Beckwith will accept orders for these products until 8/31/2022 and all products ordered must ship before 12/31/2022.
  • Please contact us to request a quote and place orders.
  • This product may have an alternative replacement product, M-3425A, depending on your application needs. Please contact us for details.


  • Microprocessor-based Generator Protection system provides 17 protective relay functions
  • Individually programmable input contacts can be programmed to activate any one of eight output contacts
  • Local and remote communications capability for both monitoring and control functions

Protective Functions

  • Overexcitation (V/Hz) protection (24)
  • Phase Undervoltage protection (27)
  • Sensitive dual-setpoint, reverse power detection suitable for sequential tripping (32)
  • Dual-zone, offset-mho loss-of-field protection (40)
  • Sensitive negative-sequence overcurrent protection and alarming (46)
  • Instantaneous overcurrent (50) protection
  • Inadvertent generator energizing protection (50/27)
  • Generator breaker failure protection (50BF)
  • Neutral inverse time overcurrent (51N)
  • Instantaneous overcurrent (50N) protection
  • Three-phase inverse time overcurrent (51V)
  • Phase overvoltage (59)
  • Generator ground fault protection (59N)
  • VT fuse-loss detection and blocking (60FL)
  • Four-step over/underfrequency protection (81)
  • Generator phase differential (87)
  • Ground differential (87GD) protection

Standard Features

  • Eight programmable outputs and six programmable inputs
  • Oscillography recording
  • 32-target storage
  • Metering of all measured parameters
  • Two RS-232 and one RS-485 communications ports
  • Standard 19″ rack-mount design
  • Removable printed circuit board and power supply
  • Both 50 and 60 Hz models available
  • Both 1 and 5 A rated CT inputs available
  • Additional trip inputs for externally connected devices
  • M-3800A IPScom® Communications Software
  • S-3400 IPScom Communications Software for Windows 7 or later
  • IRIG-B time synchronization
  • Includes Modbus and BECO 2200 protocols

Optional Features

  • Redundant power supply
  • M-3920 Target Module
  • M-3931 HMI Module
  • M-3801A IPSplot® Oscillograph Analysis Software
  • 4-Wire RS-485 Connection