During Starting, sometimes the Rotor of the motor gets Locked or Jammed which could be as a result of Bearings or Bushes or Excessive Loads, the current at that point can be 3-10 times of the Full Load rating of the motor.
When motor currents exceed 3 times of the set current value, the EOCR detects it as Locking of Rotor and trips the motor, thus preventing it from premature failures.