NEIEP Mechanics Practice Exam

How are larger motors typically started?

1. Direct current starting

2. Reduced current starting

3. Inductive starting

4. Soft start mechanisms

The correct answer is: Reduced current starting

Larger motors are commonly started using reduced current starting methods due to the high inrush current that occurs when an electric motor is initially powered on. This inrush current can be several times greater than the motor’s full-load current and can lead to mechanical stress, voltage drops in the power supply, and potential damage to both the motor and the electrical network if not properly managed. By employing reduced current starting techniques, these motors can gradually ramp up their speed and torque, thus minimizing the initial current surge. This can be achieved through various methods such as using autotransformers, star-delta starters, or variable frequency drives, which effectively lower the voltage applied to the motor at startup. Using reduced current starting not only protects the motor and associated mechanical systems but also enhances the overall efficiency of the starting process, ensuring that the motor reaches its operating speed more smoothly and reliably. This approach contrasts with other methods that may not focus on controlling the initial current, making reduced current starting the preferred choice for larger motors.