Florida Wastewater Practice Test

What should you do if a 220 volt, 3-phase motor is running backwards?

1. Check the ground connection

2. Switch the two leads

3. Replace the motor

4. Inspect the voltage supply

The correct answer is: Switch the two leads

When a 220 volt, 3-phase motor is running backwards, the most effective and immediate solution is to switch two of the three power leads supplying the motor. This action reverses the phase sequence, which is responsible for determining the rotation direction of the motor. In a three-phase system, each phase is offset by 120 degrees, and the sequence in which these phases are applied to the motor determines its rotation direction. By swapping any two of the three leads, you effectively change the sequence, causing the motor to run in the correct direction. This method is common practice in electrical work and is considered a safe and efficient way to correct the motor's rotation without the need for additional equipment or extensive troubleshooting. Other options, such as checking the ground connection, inspecting the voltage supply, or replacing the motor, may be relevant in different contexts, but they do not address the immediate issue of incorrect rotation as effectively as switching the leads.