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Complex Motor Protection
up to 450 kW

RDC-08 - microprocessor motor protection 0,4 kw

Advanced relays of protection of electric motors of the RDC-08 series have all advantages of the RDC series and considerably expand borders of its application. These relays are characterized by novelty in the field of the complex solution of protection, control and monitoring of electric equipment with electric motors of 0,4 kV and with power from 2,2 to 450 kW


The RDC-08 relay is manufactured in the metal enclosure which consists of a casing, the basis with ranks of clips for connection of current chains, chains of linear voltage which are connected to the enclosure on the device back. The relay contains terminals under the M4 screw for connection of currents of three phases and current 3I0, the supply voltage of 220 V, 50 Hz and also terminals under the M3 screw for connection of three phase-voltages of UA, UB, UC (there is a modification for linear voltage and 3U0), two analog inputs (U=0...10 V and I=5...20 mА) and the digital I2C (SPI) interface for various sensors.

Also there are terminals under the M3 screw for connection of chains of 4 output relays and 8 discrete inputs which are controlled by means of "dry contact" from the internal power supply. All connections are galvanic isolated.


  • For projection mounting with forward connection of wires;
  • For recessed mounting with back connection of wires;

The relay has execution of IP41 on the front panel and IP40 on other cover, except connection terminals, degree of protection of terminals - IP20.


  • Maximum current protection with independent and dependent characteristics;
  • Current cutoff;
  • Protection against mechanical overloads;
  • Protection against sustained start-up;
  • Protection against rotor blocking;
  • Protection against current asymmetry of phases;
  • Protection against current excess of the return sequence;
  • Protection against earth current (ground short-circuit of stator winding in operating time);
  • Protection for the minimum operating current ("dry course" - for the pumps);
  • Protection against overvoltage;
  • Low-voltage protection;
  • Protection against phases breakage;
  • Protection against distortion of phase voltage;
  • Protection against distortion of phase rotation and sticking phases before start-up;
  • Protection against reduction of insulation resistance between stator and enclosure of motor before start-up;
  • Protection against excess of temperature of motor enclosure;
  • Checking the sticking effect of contacts of the starter before start-up;
  • Automatic repeated turning on with controlled delay;
  • Remote control of motor;
  • Other functions at the request of the customer;
  • Data exchange by means of USB and RS-485 Modbus RTU.

Technical parameters

Inputs of measured current circuits
Rated three-phase/line supply voltage 150-250 V / 260-430 V
Number of phase currents 3
Number of inputs of zero sequence current 3I0 1
Rated input current of internal transformer of the current 5 А
Measure range of the current by means of internal current transformers for each phase 0,1...50 А
Accuracy of evaluation of current actuating limit, not more than 2,5 %
Transformation ratio of external current transformer 1...200
The range of the protection actuation at rotor blocking (current overload factor) 110...600 % from Irated
The range of the protection actuation for minimum current 20...80 % from Irated
The range of the protection actuation for loading current asymmetry 20...50 % from Iaverage
The range of the protection actuation for leakage current 5...10 % from Irated
Hysteresis for current (unregulated) 4...6 %
Inputs of measured voltage circuits
The number of measured voltages 4 (UA, UB, UC, 3U0)
The range of measured phase values 1...200 V
The range of actuation limit for maximum phase voltage 240...280 V
The range of actuation limit for minimum phase voltage 150...210 V
Accuracy of evaluation of actuation limit for voltage, not more than 3 V
Hysteresis (regulated) for minimum voltage 5...20 %
Other measurements
The range of measurement of insulation resistance 0,1...1,2 MОm
The range of measurement of the temperature -40...+100 °С
The range of measurement of the network frequency 45...55 Hz
Discrete inputs
The number of the inputs with ”dry contact” 8
Direct current rated voltage of internal power supply 24 V
Discrete outputs
The number of power contact outputs (16 А, 250 V at the cos φ=1) 1
The number of signal contact outputs (8 А, 250 V at the cos φ=1) 3
Information transfer
Interfaces of communication with an automated control system USB, RS-485
Protocol of information exchange MODBUS RTU
Data rate 9600...115200 bit/s
Minidisplay (OLED: 2 lines, 20 signs) 1
Light-emitting diodes 8
General data
Outside dimensions (WхHхD) 175х125х130 mm
Mass of the device 3 kg
Insulation resistance in a cold state ≥ 50 МОm
Working temperature range -40...+60 °С