Motor phase to phase short shows GF on VFD

[Saturn_Europa]

My facility uses the cheap automation direct Durapulse GS VFDs. Twice I’ve seen the drives show Ground Fault. Then the motor and the wire meg fine. In both instances I replaced the motor and the Ground Fault on the drive went away.

I’m assuming the motors had a phase to phase short and this is what caused the ground fault alarm on the VFD.

In a different instance. I’ve seen a terminal strip melt due to loose connections and the metal parts of the strip were shorting out 480v leg to leg. This would cause the ground fault meter on the switch board to switch from zero ohms to infinity constantly back and forth.

It’s my understanding that the ground fault meter on the switch board acts similarly to an Megger Insulation Tester. Where it sends a voltage and looks for a milli amp reading that it converts to M Ohms. So it makes sense that a leg to leg short would show up as a ground fault.

Do VFD ground fault indicators work in the same way ?

 

[jim dungar]

It’s my understanding that the ground fault meter on the switch board acts similarly to an Megger Insulation Tester.

Very very few Ground Fault devices work like this, except for those installed on ungrounded systems.
The majority of GF devices work by measuring the current 'going out and the current coming back' typically by passing all current carrying conductors through a single CT or by summing the outputs of several CTs.