VFD Motor Earthing

[urjaengrs]

Can somebody explain the earthing of VFD fed motors? Is normal motor body earthing is sufficient? Is earth falut curren flow back to main power supply when winding of motor gets earthed? I am asking this question as there is VFD in between main power source and motor i.e. there is conversion of AC power to DC and again conversion of DC to AC.

Please clarify

 

[wareagle]

The NEC requires an Equipment Grounding Conductor (EGC) to be connected to the frame of the equipment. The EGC is a continous connection back to the Main Switch. You would have an EGC to the motor and the VSD.

 

[controlsdude]

wareagle is correct
to detail what war is saying:
the ground of the motor case tied to the ground on the VFD.
The ground on the VFD to the ground on the main control panel.
the ground on the main control panel to the ground on the Main switch.
basically it flows like above with maybe one or two devices missing depending on how your system is laid out.
I believe grounding can be daisy chained back and not home run from these devices to the main.

 

[wareagle]

controlsdude
you are correct. My statement "The EGC is a continous connection back to the Main Switch. You would have an EGC to the motor and the VSD" sounds as if you need a individual EGC to the main. That was not my intent. The EGC is connected from the motor to the VSD to a panel frame to
other panel frames and eventually back to the main. This
connection may be in the form of a copper wire and/or metalic conduit.