The UBZ-305M is designed to protect asynchronous electric motors with a power range of 2.5 to 315 kW when using external standard current transformers with a 5 A output.
It can operate in networks with either isolated or grounded neutrals.
The device is designed for DIN-rail installation.

The UBZ-305M continuously monitors network voltage parameters, the actual phase (line) currents of three-phase electrical equipment (400 V, 50 Hz), and the insulation resistance of motors.

The UBZ-305M provides motor protection in the following cases:

• Poor network voltage quality (unacceptable voltage surges, phase loss, phase sequence errors, phase merging, phase/line voltage imbalance, network frequency drops below or rises above the set values).
• Mechanical overloads (symmetrical overloads in phase/line currents).
• Exceeding the reverse-sequence current threshold.
• Phase current asymmetry without overload, caused by insulation faults in the motor or connecting cable (comparing the reverse-sequence current asymmetry coefficient with the reverse-sequence voltage asymmetry coefficient).
• Loss of torque on the motor shaft ("dry running" for pumps), with protection based on minimum starting and/or operating current.
• Prolonged motor startup or rotor locking.
• Critically low insulation levels between the stator and the motor frame (checked before activation).
• Ground fault in the stator winding during operation, with protection against leakage currents to ground.
• Thermal overload of the motor.
• Overheating of windings (detected by built-in motor temperature sensors or external sensors monitoring the motor housing temperature).