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Drives Service & Support > PowerFlex 700 > Fault Finder

Fault Number : 38

Fault Display : Phase U to Grnd

Fault Name : Phase U to Ground

Fault Type : None

Fault Description : A phase to ground fault has been detected between the drive and motor in this phase.

Corrective Action : The U phase on the drive has been detected to have a short to ground. If your application allows, disconnect the motor leads from the drive, and shift them all left one. For example, your motor wires are U, V, and W. Put the W lead on V, the V lead on U, and the U lead on W. Rerun the drive again, and see where the fault occurs. If it stays on the same phase, then the problem is internal to the drive. Either a transistor or internal wiring have become shorted to ground. If it follows the motor lead, the problem is either in the motor or the wiring to the motor. You can put the leads back where they were, or you can leave them where they are.

Next, disconnect the motor leads at the motor. Run the drive again, and see if the fault comes back. A better test is to replace the motor with a known good motor, to see if the fault goes away. This acutally puts a load on the drive and leads, which will test them better than running with the leads themselves. Otherwise, If the fault does occur, then there is a short in the wiring from the drive to the motor. If the fault does not occur, then the problem most likely exists in the motor itself, and should be further examined. Make sure the wiring in the junction box is solid, and the wiring is intact.

A hi-pot tester can also be used to find shorts to ground. This device uses a high voltage (low current) to detect defects and breakdowns in wiring insulation.


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