Can I ground the negative DC bus of a variable frequency drive?
It should be fine but be very careful where you make your earth bond.







simulate this circuit &ndash; Schematic created using CircuitLab

You need to run the DC- all the way back to the DC supply ground point. Don't take a shortcut and connect DC BUS - to the chassis and run that back. If the DC- got disconnected the VSD chassis would go live.

Update

I forgot to explain that R1 provides inrush current limiting on power-up and RLY1 switches in when the voltage reaches half or two-thirds of normal DC bus voltage. (Thanks, Charles.)