Overcurrent and ground overcurrent protection relay
Overcurrent and ground overcurrent protection RITz-421 is intended to be used as a power system protection component to provide protection of lines or transformers. Digital technology provides high accuracy, stability and dependability.

Manuals, diagrams, technical details


Product description

Protection set

50/51 instantaneous or definite-time overcurrent protection, two-phase
51 definite-time or inverse-time overcurrent protection, two-phase
50N/51N instantaneous or definite-time ground overcurrent protection
59N instantaneous or definite-time ground overvoltage protection
67N/21N ground fault protection: directional overcurrent or ground admittance-based protection
79 auto-reclose with three cycles and switch onto fault function

Main features

  • three or four measuring inputs
  • measuring of current electrical values
  • real time clock
  • event recorder of 33 or 52 unique events witch capability of 300 records
  • parameters of last disturbance recorder, sum of tripped currents counter
  • binary inputs for external protection with possibility to block particular protection functions or auto-reclose function
  • generating of trip signal
  • LCD display and buttons set in order to operation of relay
  • optical indicating (with LED diodes) of relay operation statuses
  • 5 programmable relay outputs (S1-S5)
  • Relay output for signalling power supply module failure or lack of auxilliary voltage
  • RS-485 port for remote control with MODBUS protocol (optional)
  • self test of proper operation of relay
  • relay enclosure gives possibility to mount on 35 mm rail, surface mount or flush mount

The energising values of RITz-421 relay are currents (IL1, IL2, IL3, and I0) and residual voltage U0 (optional). If any of measured values exceeds setting value (set by user), the relay operates in a manner dependind on configuration. With optional communication interface, the measured currents, binary inputs or outputs, register logs are provided. The PC software provided with relay allows to set the relay, confirm generated signals, graphical display of measured values and browse the register records.


Rated current In 1A or 5A
Rated voltage U0n 100V
Rated frequency fn 50Hz
Nominal auxilliary voltage Up 24V DC, 48V – 60V DC,
110V – 230V DC/AC
Control voltage Us acc. to aux. volt.
Setting range of threshold current
(0,05÷5)In or (0,2÷20)In for 50/51 protection – def.time char.
(0,05÷0,5)In or (0,2÷2)In for 51 protection – inv.time char.
(5÷500)mA or (0,05÷2,5)A for 50N/51N protection – def.time char.
Accuracy of current inputs 2,5%
Setting range of treshold value of sum of tripped currents counter (100÷65000)In
Setting range of timers
(0÷99,99)s for definite-time characteristics
  • according to A, B, C characteristic defined by EN 60255-3 regulation
Pick-up time ≤40ms
Burden in analog inputs ≤0,5VA/wejście
Burden in auxilliary voltage supply ≤6W
Continous thermal withstand of current input 2,2In
1 sec thermal withstand of current input 80In
Dynamic withstand of current input 200In
Relay outputs data (S2 – S5)
Max. breaking capacity by U=250V
– resistive load 0,3A
– inductive load of L/R=40ms 0,12A
Max. breaking capacity by U=250V, 50Hz
– inductive load of cosϕ=0,4 3A
Continuous contact carry 5A
Relay outputs data (S1, watchdog contact)
Max. breaking capacity by resistive load
– AC current 6A
– DC current 6A/28V; 0,16A/220V
Continuous contact carry 5A
Ambient temperature (268÷313)K/(-5÷40)°C
Relative humidity ≤ 80%
Ingress Protection degree IP40
Weight 0,8kg
Dimensions (height x width x depth) 75 x 100 x 120 mm
Electromagnetic compatibility according to PN-EN 50263
Insulation according to PN-EN 60255-5

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