When checking the voltage or current unbalance, the motor should be left on.

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Multiple Choice

When checking the voltage or current unbalance, the motor should be left on.

Explanation:
Measuring voltage or current unbalance is meaningful only while the motor is running under its normal load. When the motor is energized, the phase voltages and currents reflect the actual electrical stresses it experiences, including any unequal distribution among the three phases. This unbalance can create negative-sequence currents, extra heating, vibration, and fluctuating torque—issues that protection systems and monitoring devices are designed to detect. If you shutdown or power the motor off, you lose the operating condition, and the readings won’t reveal the imbalance that would occur in service. So, keep the motor energized and running during the check to obtain meaningful, actionable data, using proper instruments to capture the phase voltages and currents.

Measuring voltage or current unbalance is meaningful only while the motor is running under its normal load. When the motor is energized, the phase voltages and currents reflect the actual electrical stresses it experiences, including any unequal distribution among the three phases. This unbalance can create negative-sequence currents, extra heating, vibration, and fluctuating torque—issues that protection systems and monitoring devices are designed to detect. If you shutdown or power the motor off, you lose the operating condition, and the readings won’t reveal the imbalance that would occur in service. So, keep the motor energized and running during the check to obtain meaningful, actionable data, using proper instruments to capture the phase voltages and currents.

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