Old Lathe Electrical Question

[Steve Kirincich]

Hello,

I purchased an old Oliver lathe a number of years ago, and it came with a DC motor and a controller/converter that lets me adjust the speed. While using it recently, I experienced a slight shock when running the lathe and touching the tailstock screw handle with my right arm. While running, i connected a volt meter to the chromed handle and the outlet box and got a reading of 55 volts. This number drops to 5 volts if I stop the rotation and drops to 0 volts if I turn off the power to the controller/converter. Is this a grounding issue? A few photos have been included.

Thanks,
Steve

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[Richard Coers]

55 volts is a lot. Sending that to a ground rod should trip the breaker shouldn't it? Is that 55 volts AC or DC?

[Julie Moriarty]

After we had a lightning strike on a jobsite I was working on, I got a 50 volt reading to ground on the doorknob of the iron workers trailer. The trailer was properly grounded but nothing tripped. (long story)

It's possible your lathe has an open leg or at least a leg that has more resistance in it than the ground. Check all the wiring connections and the wiring itself. Look for anything that's loose or any wire that may have a nick in it.

[Maurice Mcmurry]

Steve, What is the primary voltage of your DC motor controller? If it is 120 volts, it could be a result of the rectifier creating a neutral - ground short. Neutral AC and negative DC are not synonymous.

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[Steve Kirincich]

The DC motor controller is plugged into a 240 volt outlet. The 58 volt readout was measured with the meter in AC mode. Thanks to everyone who has responded!

[Maurice Mcmurry]

Does the machine have only the DC motor?

[Steve Kirincich]

The DC motor is the only motor and gets powered by a rectifier.

[Steve Kirincich]

I checked the wiring and then checked with the volt meter. Perhaps magic but I now do not get any strange voltage readings.

[Maurice Mcmurry]

It is a quirky mystery that I just like to think about. Is any dust collection connected? Were any other appliances running when you got shocked? I had some clients who had electrical problems that occurred when the electric cloths dryer was running. Turns out the neutral wire of the direct burial service entrance had turned into dust, the running dryer, completing the circuit, exposed the problem.

[Steve Kirincich]

I am fairly certain that no other appliances were running at the time, but since the problem mysteriously disappeared, I am assuming that it will rear its ugly head eventually.

Thanks!

[Richard Coers]

Did you ever call your utility company? They could certify the lines up to your house and probably verify the connection at the house and might just include viability of the major ground rod and connection by the meter.