LT Motor Protection Relay UBZ-302


Motor Protection Relay –

Power (Watts or HP) 2.5kW – 315kW (4HP – 500HP)
Motor Voltage 380V – 415V AC
Motor Brand Any
Phase Three Phase AC
Communication Built-in RS232 & RS485 Modbus/ASCII communication
Voltage Type AC
Operating Voltage (V) 320V – 480 V
Number of Poles 3 Pole, 4 Pole
Application Three phase LT motor protection with built-in CTs (upto 63A motors), Above 63A connect external CT
Rated Current (Amps) 5A to 630A programmable
Output Type Programmable relay – SPDT (1NO+1NC) 16A and Power Relay – DPDT (2NO+2NC) 8A

10 in stock


UBZ-302 has been designed for protection of asynchronous induction motors ranging from 2.5 kW to 30 kW that use of integrated current transformers and 30 kW to 315 kW through use of external current trnsformers, including in circuits with insulated neutral.

UBZ-302 provides for electric motor protection in case of:

  • poor quality supply voltage (unacceptable voltage surges, phase loss, incorrect phase sequence and phase coincidence, phase/line voltage imbalance);
  • mechanical overloads (symmetrical phase/line current overload);
  • exceeding the negative sequence current threshold;
  • phase current imbalance without overload, induced by the insulation fault inside the motor and/or the lead cable (the current imbalance factor is compared to the voltage imbalance factor using negative sequence);
  • loss of motor torque (“dry stroke” for pumps) – protection based on the minimal starting and/or operating current;
  • delayed motor start or rotor locking;
  • abnormally low insulation level between the fixed coil and frame (testing before motor startup);
  • ground fault of the stator coil during operation – protection against ground leakage current;
  • motor thermal overload;
  • coil overheating (measuring the coil temperature with integrated temperature sensors, or the body temperature with external temperature sensors).

For each protection type, automatic reclosing (ARC) can be enabled or disabled.

The device provides for electric equipment protection by means of controlling a magnetic starter (contactor) coil.

The device detects the presence of load currents when the load relay is open (when the load relay is open and the functional relay is in the star-delta mode). In this case the Unit initiates the alarm of external Magnetic Starter (further in text as MS), which starts the engine, until the unit or the control of engine currents are switched off while the load relay is deactivated.


– control and parameter transfer via the RS-485 interface using the MODBUS protocol;

– control and parameter transfer via the RS-232 interface.

Availability of another output relay allows for an additional operation mode:

  • Star-delta switching
  • Delayed start power-on (for example, cascade motor starting)
  • Remote signaling system relay

Additional Information:

  • Port of Dispatch: New Delhi, India

Technical Specifications:

Rated supply voltage: three-phase380/415V
Mains frequency, Hz48-62
Rated currents range (when using integrated current transformers), A5-63
Voltage hysteresis, (phase/line), V10/17
Thermal hysteresis, % of accumulated heat at shutdown33
Current tripping threshold detection accuracy, % of rated current, ≤2
Voltage tripping threshold detection accuracy, V, at least3
Voltage based phase imbalance detection accuracy, V, at least3

Minimum operational voltage:

– single-phase voltage power supply, with connected neutral wire, V, at least

– three-phase power supply voltage, V, no more than



Main outputs

– load relay –two groups of changeover contacts for motor starter control – 8A, 250V at cos φ=1;

– functional relay – one group of changeover contacts –  16A, 250Vat cos φ=1 (relay function assigned by the user)


Analog inputs

– two analog inputs for temperature sensors (type Pt100, Ni100,Ni120)

– analog input for sensor with 0-10 V output

– analog input for sensor with 4 mA (0mA) – 20 mA output

– three analog inputs for standard CT with 5A output (type T-0.66 or similar)

– input for differential current transformer (zero sequence transformer)

Temperature sensor resolution,  °С1
Power consumption (under load), VA, no more than5.0
Weight, kg, no more than0.5

Dimensions (figure 1.1)  -nine S type modules

Mounting – on a standard 35 mm DIN bar

Mounting position – any

Characteristics of output terminals of integrated relays:


Operation modeMax. current at U~250VN of trippingx 1000Max. commutated powerMax. additional alternating voltage

Max. current at Uconst=30V

(N of tripping)

functional relay

cos ф = 0.4

cos ф = 1.0

5 A

16 A

1004,000 VA440/300 V

3 A

load relay

cos ф = 0.4

сos ф = 1.0

2 A

8 A



1,000 VA460 V

3 A (50,000)

UBZ-302 complies with requirements of:

IEC 60947-1; ІEC 60947-6-2; CISPR 11; IEC 61000-4-2

Hazardous substances in excess of maximum allowable concentration – absent

Additional information

Weight 0.7 kg

8 pole MCB size (W:156.5 x H:90 x D:52 mm)




DIN Rail


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