[guru_florida]

Bought a Chinese VFD and it has only a 3 pin connector (expected). Heard a lot about needing to add a ground connection and people opening up the motor to convert the connector to 4pin. I can't seem to find anything definitive about it now (go figure). Using a continuity tester the casing of the 3pin connector is connected to the motor casing and the spindle right down to the ER collect holder. Also, there is no continuity between UV or W to the shield (good). So it seems to me that the connector casing is already connected to the spindle, and I can just connect that back to the VFD ground connection using the wire shielding. Typically the wire shielding is only connected on one side but seeing as this ground is not electrically connected to anything in the motor so I wont be forming a ground loop. Or should I be connecting it to Earth ground instead not VFD DC-bus ground?

[mactec54]

Bought a Chinese VFD and it has only a 3 pin connector (expected). Heard a lot about needing to add a ground connection and people opening up the motor to convert the connector to 4pin. I can't seem to find anything definitive about it now (go figure). Using a continuity tester the casing of the 3pin connector is connected to the motor casing and the spindle right down to the ER collect holder. Also, there is no continuity between UV or W to the shield (good). So it seems to me that the connector casing is already connected to the spindle, and I can just connect that back to the VFD ground connection using the wire shielding. Typically the wire shielding is only connected on one side but seeing as this ground is not electrically connected to anything in the motor so I wont be forming a ground loop. Or should I be connecting it to Earth ground instead not VFD DC-bus ground?

No you can not use a shield as a Ground, a Ground wire has to be a wire either using a 4 wire cable plus shield, ( which is best ) or an independent Ground wire which can run with the VFD to Spindle cable, I'm no sure why people keep buying 3 Pin plug only spindles, if people stopped buying them then they would go away

All Shields connect to Earth Ground

[dharmic]

Depends what you're trying to achieve. If it's just a bit of noise suppression, strapping cable shielding to the case at the motor and back on the VFD ground or the controller's grounding star point should be fine.

I found with my cheap router that the whole machine was floating and ended up just strapping the frame to mains earth which fixed a few problems.

[guru_florida]

Thanks mactec. I also found your other thread with thecarpenter. I tried to open the connector side of the spindle by removing the 4 screws but I couldnt get the top off. I hope they didnt thread-lock it or something. I don't know where the 4pin versions of these cheap chinese spindles are, I looked pretty hard for one before settling for a (likely) 3pin and deciding to convert it once I got it. Yes, it would be nice if China just did it right in the first place but good luck with that. lol.

I hooked up the spindle with the 3 conductors only and it all works. Just spun it for 30 seconds no-load and no water cooling. Now I'll go back to converting it as you advise. I am still thinking I dont need a 4pin connector though since the connector housing on the spindle is connected to the spindle shaft, etc. So I can add a 4th core to the cable and connect that to the connector shield on the spindle side. The cable shielding will be connected to earth ground VFD side and not connected spindle side. Now does the 4th ground connector go to earth ground on the VFD as well or controller (DC-bus ground)? I assume it should be earth ground as well. The ground next to the UVW wires is only earth ground, it is not a normal DC-bus ground.