You are replacing a three-phase induction motor in an application where equipment could be damaged if the direction of rotation of the motor is incorrect when connected. Assuming that even momentarily jogging the motor could damage equipment and that the feeder phase sequence is ABC clockwise as tested with a phase sequence indicator, what should then be done to ensure that the motor rotation will be correct (clockwise) when connected electrically to the line and mechanically to the load? Assume that the power is off and that the contact-type motor rotation indicator leads are connected to the motor terminals.
• Three-phase induction motor rotation and phase sequence (ABC vs ACB) • How a motor rotation indicator compares mechanical shaft direction to electrical phase order • Effect of interchanging motor leads on direction of rotation
• If the line sequence is known to be ABC clockwise, what must be true about the motor’s internal phase order for the shaft to turn clockwise when energized? • When you spin the motor shaft clockwise by hand and use a rotation indicator, what reading (ABC or ACB) would tell you that the motor’s electrical rotation matches the mechanical direction you are turning it? • Does correcting an incorrect direction of rotation require swapping all three leads or just two, and why?
• Confirm how many leads need to be changed to reverse a three-phase motor’s rotation (any two vs all three). • Verify which phase indication (ABC or ACB) on the tester represents agreement between the mechanical direction you turned the shaft and the motor’s electrical phase sequence. • Make sure the statement about agreement/disagreement between the tester reading and motor rotation matches what actually happens in three‑phase motors.
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