GROUND FAULT on GMT Water Cooled Spindle
 

Hey all. I've been running my MechMate with no (major) issues since November of last year. Now, seemingly out of nowhere, I am getting a Ground Fault error on my VFD. The spindle will run for about 5 minutes and then throw the GFF error code.

I have a GMT 2.2kw water cooled spindle and a Delta VFD-M Inverter.

I have the ground pin on the spindle and the cable shield connected to the ground terminal on the VFD. I checked my wiring and nothing seems to be loose. I blew out the VFD just in case there was something inside that was shorting out the connectors.

Anyone have suggestions as to how to troubleshoot this?

You are bleeding current to ground somewhere. What is the ohm reading of your motor from phase to phase (a to b, a to c, b to c)....then check each to chassis of the motor. You should not have any deflection at all and a with a DMM it should be read open (Fluke shows OL) If you have mega ohms, you have a path to ground. A Meggar is normally used for this application.
Next move onto the Load cables, unhook from VFD then check continuity to each other (without them touching on either end) it must be infinite. Then check them to ground.

If you have a spare amount of cable even if it is short, quick wire it to the motor and test run it. That will tell you if it is the cable in the cable tray.

Pardon my ignorance, but I need a few things explained a little better. I'm still learning the terms/names of electronics parts and how to use the multimeter.

When you say "What is the ohm reading of your motor from phase to phase (a to b, a to c, b to c)", do you mean to measure the cable at the VFD end? Or do I measure the pins of the spindle? I think I understand to measure the resistance between the a/b/c conductors but not clear WHERE to do that.

As far as using a "megger", I don't own one nor know anyone with one. Is it necessary to have one to troubleshoot this problem?

Yes the pins on the spindle. You have 3 legs. A B C or X Y Z or U V W. depends on the manufacturer. You are checking the windings for an even reading and no reading to ground pin or chassis of the motor from any of the windings.

You also need to unhook the motor supply cable which would be attached to the load side of the VFD and unhook from the motor. You need to check if your insulation has become compromised. Check each wire for continuity (to check attach probe to same wire on each end) then check for open circuit between any two wires (this should be open) a total of 6 checks. Just make sure the wires are not touching.

A megger is not required but will show the most stubborn breakdowns in winding insulation and wires that typical do not happen until the item is flexed or heats up. I have used a megger less than 10 times in my career in industrial maintenance (about 20 years now). The problem is 99% of the time found by other troubleshooting means.

I should have said this first. All these checks require power to be off. And be careful, we always say. ... electricity doesn't kill but rather it is the idiot playing with it that gets killed.

I had an issue with my VFD/spindle where the plug on the spindle had a loose wire. Took ages to find it but once I did it has been good ever since. Maybe you could check that?

Checking the connections and the pins on the spindle plug was the first thing I did. When I installed the plug end I made sure all the pins were soldered to the cable's conductors. All the soldered joints still look good.

Thank you everyone for your suggestions. I will try these out today and report back. Crossing my fingers!

That's the thing - the spindle DOES work for about 5 minutes or so before throwing the error code. I let the spindle run for about 30 minutes with no load and it didn't stop.

Try air cutting with motion. Use the file that caused the error, just in case there is a short that happens when in motion

Philip, what is the displayed fault code? Sometimes calling the factory for technical support about the error code can be worth while. They will want to know what steps you have taken so far.