The Holiday Inn in downtown Binghamton, NY was hit severely by the 2011 flood. Their whole basement mechanical room was completely underwater, including their VFDs. 
One of the casualties was a Toshiba G3+ 350 HP VFD. The drive runs their Carrier 350 ton Chiller for all of the air conditioning in the building. The drive was replaced with a new Toshiba HX7 Plus Pack VFD, the motor checked out, and new wires run to the motor.
EMA was called in to perform factory startup on the Toshiba HX7 Plus Pack VFD. The “startup” quickly turned to more of a troubleshooting call once the VFD was powered on. Attempting to run the VFD resulted in an “Earth Fault”. The motor/wires were re-meggered on 1000V scale to ground = 2200 Mohm, the VFD ran ok and had a balanced output voltage waveform with no motor attached. When Carrier specifies a VFD for their chillers they also require this “GFD” module be included. On further inspection of the GFD module the following was found.
The input to the GFD module is taken off center tap of the DC bus via four ten to twenty watt resistors in reference to ground. The output is a set of contacts off a small relay on the GFD circuit board.
I took oscilloscope measurements of the input to the GFD board and had a meter on the relay contacts off the board. I ran the VFD, which immediately tripped on Earth Fault again even though the input to the board stayed at zero volts and the relay contact never closed.
To verify the trip was coming from the GFD module the relay contact could be jumpered and the VFD would show an Earth Fault. The 24VDC from the logic board feeding to the relay contacts on the GFD board was disconnected. Ran the VFD; still had an Earth Fault trip. Traced the wires back to the Master Gate Drive board from the relay output on the GFD board, and disconnected the wires at the Master Gate Drive board.
I then ran the VFD, which ran well without trips. Upon further inspection, those wires from the GFD circuit to the Master Gate Driver board were zip tied along fan power wires. Once the drive is called to run the eight cooling fans in the VFD would kick on, induce noise into the wires to the Master Gate Drive board, and cause the nuisance trip. The wires were re-routed, connectors reseated and the VFD ran well.
We find this situation occasionally, and it’s a reminder to exercise good engineering practices in wiring and cable runs. EMA services nearly all brands of VFDs, and performs service on everything from standalone VFD s to coordinated drive systems. Contact your nearest EMA facility as listed at the bottom of this page, or hit the contact icon on the top right.