Detecting correct Phase sequence for unidirectional motor

A phase rotation meter, through the use of its six terminal leads, compares the phase rotation of two different 3-phase connections. Three leads, labeled "A," "B," and "C," are connected to the test unit's side labeled "MOTOR." Three other leads are labeled the same but are connected to the test unit's other side, which is labeled "LINE." The meter also has a zero-center voltmeter, with one side labeled "INCORRECT" and the other labeled "CORRECT."

First, you "zero" the meter per the manufacturer's instructions. Then you position the meter's selector switch to "MOTOR" and connect the three MOTOR leads to the motor's leads. Finally, you hand-turn the motor's shaft in the desired direction while watching the voltmeter, which immediately will swing to the CORRECT or INCORRECT direction. A special note: Although the needle will swing in the opposite direction after the shaft stops turning, you should use the voltmeter's first indication as to the status of rotation direction.

If you're lucky and the first connection configuration is correct, you label the motor's leads "A," "B," and "C" to coincide with the connected leads from the phase rotation meter.

Suppose you're unlucky and the voltmeter reads INCORRECT. Then you should swap any two of the MOTOR leads and hand-turn the motor shaft again. Now, the voltmeter should read CORRECT, and you should label the motor's leads "A," "B," and "C" to coincide with the connected leads from the phase rotation meter. You're not done yet, though, with the motor installation.

Determining rotation of power source line
Now, you have to verify the rotation of the line supplying power to the motor. Your phase rotation meter can be used here, also.

After deenergizing the motor's power feeder and applying required lockout/tagout devices, you position the unit's selector switch to "LINE" and connect the three LINE leads to the feeder. Then, energize the feeder and watch the voltmeter.

If you're lucky again and the voltmeter reads CORRECT, you label the power feeder leads "A," "B," and "C," after the feeder is deenergized and with lockout/tagout devices again installed, to coincide with the connected LINE leads from the phase rotation meter.

If you're unlucky again, you deenergize the motor's power feeder and apply required lockout/tagout devices, and swap any two LINE leads. With the feeder reenergized, the voltmeter will read CORRECT. Now, you can label the feeder conductors "A," "B," and "C" to coincide with the connected LINE leads from the phase rotation meter.

All that's left to do is to match the labeled motor leads with the labeled power feeder conductors and make the required connections. The motor will run with the right rotation.

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