I'm measuring the voltage interrupting the ground wire that goes from the motor frame to the grounding circuit, and connecting the one probe of the ac voltmeter to the frame and the other to the grounding circuit.
I also tested other motors and I keep having the same issue.
dpc, it occurs at all operating speeds from the minimal (500rpm) to the maximum (1700rpm). The motor is well grounded, and I'm measuring voltage from the frame-toground with a clapm meter.
I have a VFD connected to a small motor (5 HP). The motor operates fine when its not connected to the VFD, but when it operates connected to the VFD (and with no load) it intermittently vibrates and it has a frame-to-ground voltage of about 50 Volts. What could be the problem, and how do I fix it?