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Bad machine ground connection and how I was able to test it.

The CNC machine I had the problem with was a small Milltronics vertical with a PC based control. The CNC machine had been having a lot of unexplainable problems and alarms. They had swapped servo motors, spindle drives and more. Being that the alarms were far and in-between and inconsistent I decided to inspect the grounding of the machine.

I had taken a piece of emery cloth and polished the ground rod and checked with my meter from the ground rod to the machine terminal strip. What I found was a 2VAC difference between the ground rod and the back plain or ground terminal strip in the machine. After further inspection I found was that the transformer was grounded and there was no ground wire going to the machine. The machine was only grounded through the flexible sealtight that was attached to the transformer.

I polished up the transformer ground connections as well as run a ground wire to the machine. Rechecked with the meter and the voltage difference disappeared. Followed up with the company about three days later and all seems to be going well.

Anyone else have other tips on finding noise or grounding problems?