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The VFD Answer Man, Volume 5: Earth Faults and ABB

December 20, 2015 |By: Terry M. Smith

On all ACH550 drives leaving the factory there is a new program parameter that allows you to set the ground fault detection level.  Parameter 3028 allows you to select 3 levels: Low, Medium; and High. The default setting is Low. In the event of an earth fault issue try setting to Medium. The problem will probably go away.

If you try High and the fault persists we need to:

1. Megger check the motor.

2. If it megs out OK we need to recommend a motor surge test. This should show if there is a phase to phase winding failure. The megger test cannot detect this. The surge test requires a special tester that most electric motor service shops have. For motors under 25 HP I recommend replacing them and sending them to a shop rather than going through the expense of the surge test.

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