I'm an electrician working for a major university. I was told by our stationary engineer to meg out a motor because he was getting "ground fault" errors on his VFD.
I said okay I'll meg out the conductors from the vfd to the disconnect first then from the disconnect to the motor second. The first meg went okay i got 9.99 meg ohms (1k megohm meter). The second test (disconnect to motor) through me for a loop. I got .04 on all three legs to ground. I took out my volt/ohm meter and got a low resistance to ground reading also. I tried the same tests on a good motor nearby. Same readings! The stationary engineer says that the first motor i megged was going bad, but i megged almost a brand new motor and got the same readings. I would like to know if there is a certain reading/value i should be looking for in a motor. The stationary engineer said anything below 4k between phase ground. My real question is how do i properly check insulation of a motor and how do I check to see if the motor is still good (no matter what meter i use)
