Sparks Flying! AC on the Servo Housing

[roundel325]

I'm setting up a ProLight 2000 mill with Acorn and DMM DNY2 servos. Bench testing of Acorn and servos went well. Got everything wired up in the cabinet and Acorn/CNC12 are working as expected. Ran some gcode cutting air. Was able to tune the motors with DMM's software. I was ready to move onto wiring up the DC spindle controller but decided to put a dial indicator on the table and verify my turns ratio settings. When the indicator came in contact with the spindle there were sparks and the x axis started to jerk around. My multimeter shows 30-35v AC when probing between any two servo motor housings. I talked with DMM on the phone and they thought the negative DC supply might be earth grounded but it is not. I did have the common terminal grounded but disconnected it and no change. Curiously, the ground lead in the motor cables doesn't connect to anything at the motor connector (maybe it's just for shielding?).

I've been working on it all day and I'm stumped. I'm using DMM 's premade motor cables, Antek 48v linear PS. Following very closely Marty's Emcoturn 120 build. Does anyone know what might cause a servo housing to be electrified?

Thanks!

[deanq]

If the shield on ANY of your cables is grounded, try disconnecting the shield ground, particularly the power leads from your drives to the servos. I used shielded cable for most all connections on my Bridgeport, and I had quite a few issues traced back to shield grounds, including the issue you are seeing. I also am using the DMM Dyn2 drives/cables. Err on the side of no shield grounding for Acorn connections.One of the few places I used the grounded shields was for the VFD power and control cables (not applicable in your case). YMMV, just my experience with Acorn and the Dyn2 drives.
Dean

[roundel325]

Thanks for the tip. The only grounded shields I had is the motor cables and the step/dir leads from acorn to DYN2. I disconnected them and did not see any improvement.

[roundel325]

Posting now to close the loop. DMM determined that a batch of their Nema 23 motors have faulty insulation on the motor frame and they are sending replacements.

[martyscncgarage]

Posting now to close the loop. DMM determined that a batch of their Nema 23 motors have faulty insulation on the motor frame and they are sending replacements.

Wow, thanks for the follow up and info on the motors...