Just a thought
I noticed before that the buss voltage was low
At the time I didn’t know what the fault 4 was
Somebody here said it was low buss voltage
It’s odd for 2 VFD’s with the exact same problem showing the exact same fault makes me wonder
Is there a line contactor in front of the VFD or a breaker inline
Check that the contactor or breaker is closing correctly (all 3 phases ) one may not be making full connection
A bad connection on one leg may cause the buss voltage to stay low the control may read it as high enough to run but too low to run correctly. I think that Power Flex drives use 2 incoming phases to power the controls if the third leg was low or missing I don’t know what would happen.
I have seen other drives run at reduced power with a single phase line input
I don’t know if they even check for incoming phase loss I know some drives don’t check or care.
And with some driver they give you the option to disable incoming phase loss fault
It think it would be worth it to check it out
it's a definitely good thing to check and ensure that the wiring is accurate.
Story time -
I was helping support over the phone a customer who had a bad PF527 drive, and they attempted to replace it. it was being run as a motion axis in the program, and was using safe torque off over ethernet, etc... all the things.
every time it was tried to run it would fault for overload. Well the first thing up was to tell them to take the U-V-W leads off and check the motor and ensure it's spinning freely (if possible), do a quick check of resistance on the motor, make sure it's not bad... I was told it was good to go, and they put it back on.
I was remote connected in and attempting everything I could to see why this was failing. nothing had changed that we knew of, and nothing programmatically changed so it made no sense at all. We even called up and double remote supported with rockwell over the phone and their guy couldn't get to the bottom of it.
Until Finally, they had another drive they wanted to try, and I said of course, go ahead and throw it in, and what do you know, over the phone I can hear ... "Hey, who hooked this up!?!? they wired it up backwards!".
for almost 2 days of support time, they had a "throw away" tech doing the hand work, while the supervisor was relaying the info for troubleshooting, and he was relaying it back through. Apparently he had hooked up the L1-L2-L3 and U-V-W backwards, and it didn't blow the drive up...It didn't even fault until you tried to run!!!!!
They swapped the leads around and it took off no problem. After being told to check the connections multiple times, and having them remove them multiple times, and not a single time did anyone realize they had wired it wrong because it powered up every time...