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Originally Posted by AutoPilot

The next thing you should look at is for a control relay or other device powered from the 24vdc on terminal 10 and 12 DCOM. This will usually cause other types of faults as well as Earth Fault.

@Autopilot, I'm working with a customer to install PLC-like control devices on a pair of ACS550's running farm fans, and we are getting intermittent ground faults when we use the control device's relays to start and stop the motor, with the 3-WIRE macro. He had no issues when starting the fans manually through the VFD control panel in manual mode.

Worth noting: he has two VFDs right next to each other, and each has its own control device. When operating, the control devices are synchronized, so one starts the first fan, and then 5 seconds later, the other starts the second fan.

Our wiring setup for 3-WIRE macro:
- External speed reference jumped to 10V DC reference (to run full speed)
- GND (11) to DCOM (12)
- 24V (10) to normally-open START RELAY to DI1 (13)
- 24V (10) to normally-closed STOP RELAY to DI2 (14)

I'm expecting we'll need to get a technician on-site, but I was curious about your relays comment. Any thoughts on how to avoid ground faults when using a relay near terminal 10 and 12 like we are?

also multiple motors or line and load in same conduit can also generate ground fault alarms.

parameter 3028, you can adjust the sensitivity of ground fault. set to high for low sensitivity. there are two other parameters that can be changed for ground fault but they can void warranty. you need to contact ABB and have case#. you will also need to work with local factory service rep.

i encountered same problem once and i disconnected wiring from drive and motor and found resistance from wiring to conduit. would only happen after a rain storm. conduit was old and full of water. electrician didnt believe me and kept condeming new drive because his meter wasnt showing it. he ran temporary whip fromdrive to motor. about 100 ft same problem. i said bro u are still using ground from original conduit. finally i talked customer into replacing conduit and wiring. never had fault again

From the drives to the tower - do any of the lines from the separate drives come in close contact with eachother (ie. common feed to tower then split off to the individual motors)? The 24v measured in the dead line is being generated from an active line by it's field). Also, the motor megger reading - is this a dry reading or during a time after the motors have been operating then shut down for testing? I'm assuming that the motors are on induced draft towers and in vapor paths.

I have started many ACH-550 Drives. On Smaller motors, almost every time I've gotten a call back after a few weeks or months of operation I'll actually open the pecker head and look at the connection. If its just wire nuts and not crimp connectors This is the most likely Earth Fault problem.

The next thing you should look at is for a control relay or other device powered from the 24vdc on terminal 10 and 12 DCOM. This will usually cause other types of faults as well as Earth Fault.

Also if the motor wiring is over 100 feet the wire gage could be too small especially if it's solid wire. That paired with wire nuts will cause other strange problems as at higher frequencies the current travels along the outside surface of the wire. Check that parameter 2601 (Flux Optimization) is turned off in this situation.

Sounds like you're on the right track.
Looks like I haven't been much help. But then, I don't think you really needed it....

Nuclrchiller, just got back in from checking the drives, and one thing interesting both drives share a common ground. Or I should say both drives are tied into a common ground while playing with the drives, I put drive three into hand while drive four was running and as soon as drive three started ramping up, drive four went into earth fault. This was not a one occurrence for what it is worth, I then undid the ground wires and tried again, same problem but I noticed that between the drive ground and the panel ground I was picking up 24volts. This happened on both drives, I am about to call ABB again to discuss where this voltage is coming from and why I am getting it. And to answer your question about the motor, no it is not in the airstream nor water spray the motors are outside the tower under a hood. And as far as megging goes that is exactly what I did when testing I wanted to make sure I isolated and possible problem, so after the first test I went back and separated all electrical components and tested as well.

700 megohm on a 460V motor is what I believe most would consider marginal, but acceptable. But, apparently, not ABB.
What type of cooling tower is this? Is the motor located in the airstream? If so, before or after the air flows through the water spray?
I would proceed by breaking electrical connections and isolating all components to find where the lowest megohm reading is. Such as in the motor, the wiring from the drive to the motor, and if a disconnect is between the drive and motor, meg the wiring runs separately and the disconnect itself (also separately).

Nuclrchiller, good question I megged the motor back at the drive. Disconnected the output side of the drive and tested from the drive up to the motor.

Where did you meg the motor? The peckerhead? Did you include the wiring and disconnect from the drive to the motor? Did you disconnect the output leads from the drive?

ABB and fault 16 !!!!!!!

Wondering if anyone could give me some insight. I have two new Abb drives (ACH 550's) on a 6 month old cooling tower. The motors are 10 hp 460 volt, I keep getting a fault code of 16 (Earth ground Fault) I have megged the motors out both motors megged above 700 megaohms, when I say both yes I have issues with both drives on the tower. They might run two weeks then fault out, they might run two days then fault out. I called ABB and was told there must be moister in the motor, and to meg out this would tell me. From what I have looked at and tested I have found no moister. From the drive to the motors on the tower is approx 100 to 150' ft run of wire, I have also been told there is a chance of capacitance build up in the wire,. If so would a load reactor help my issue. For what it is worth we have another tower that was replace about a year ago and I had the same issue with the motors on that tower for about a month, after it was started but the problem went away and has not come back.
Any feed back would be greatly appreciated
Thanks,