How to Change a 3-Phase Motor

Typically powered by either 240 VAC or 480 VAC, 3-phase motors are also capable of being powered by both voltages if so denoted on the metal identification tag. The electrical tag is generally mounted to the outside of the motor housing and at the top of the round frame. Attention must be paid so the correct motor is replaced. Certain frame mountings and physical sizes are different even in the same horsepower ratings. RPM (rotations per minute) must also be noted, as motors of the same physical dimensions may have a different speed. Before replacing any 3-phase motors, the existing motor's pecifications must be recorded. The replacement must be of the exact same size, horsepower, speed and type. Failure to do so can result in damage to machinery or an injury.

Things You'll Need

• Screwdriver
• End wrenches
• Wire strippers
• Wire pliers
• Wire nuts
• Electrical tape

Instructions

1. Confirm that the replacement motor is the correct speed, horsepower and frame size. Remove all electrical power from the motor. In the case of an industrial setting, Lock Out and Tag Out (LOTO) the electrical source. LOTO is a safety procedure mandated by OSHA (see Resources).

2. Open the electrical cover to the motor with the screwdriver. Remove all wire nuts from the main power wires. Make note of connections if you are unsure of the rotation for the motor. Pull the main power wires from the electrical box.

3. Use the end wrenches and pull the frame bolts from the motor's mounting plate. Mark the position of the motor if a shaft coupler is employed for connection to any driven devices. Remove the old motor.

4. Install the new motor onto the mounting plate. Align the shaft coupler to the shaft of the driven device. Install any new pulley belts, if applicable. Leave shaft coupler or belts unconnected if you're unsure of the new motor's rotation.

5. Terminate the new motor to the main wires. Strip back the wires using the wire strippers. Twist the correct pairs of wires together. Use your notes made in the above steps for a proper connection. Apply a wire nut over every exposed bare wire connection. Cover each wire nut with an insulating round of electrical tape.

6. Test the motor's rotation by "bumping" the motor with power. Change the rotation of the motor by interchanging any two of the main power leads. Bump the motor again. Install the drive belt or shaft coupling onto the driven device.

Tips & Warnings

• You can pre-wire the inside of the motors junction box for certain voltage applications. This can save time in an industrial setting.

References

• Bureau of Reclamation
• "Industrial Motor Control"; Stephen L. Herman; Walter N. Alerich; 1985

Resources

• Lock Out and Tag Out