A faulty rectifier can give you a DC earth fault.

>>>Earth faults are very hard to find, they come and go, so you have to monitor over an extended period.
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>>Will do. Thanks.
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>An earth failure will not create the errors in the pictures that you see. The power lines carry AC, which in the event of an earth failure will result in a alternating magnetic field. You will need DC to create a stable magnetic field which may cause the errors you reported.