Question 306Electricity & Electronics - Assistant Engineer

The correct answer is C) clamp-on ammeter. A clamp-on ammeter is a useful instrument for checking 3-phase AC motor performance by measuring possible unbalanced currents. It can easily measure the current in each of the three phases, allowing the operator to identify any significant imbalance that could indicate a problem with the motor or its power supply. This is an important diagnostic tool for maintaining the proper operation of 3-phase AC motors. The other options are not as well-suited for this task. A D'Arsonval iron-vane probe (A) is generally used for measuring voltage, not current. A hand or battery-operated megger (B) is primarily used for testing insulation resistance, not motor current. A vibrating-reed frequency meter (D) is designed to measure frequency, not current.