A friend (Tim) has a General lathe with 220 v motor wired to a variable speed controller . The lathe bed became energized and tested at 94v.  A machinist club member tested the controller and lathe motor and thinks the controller has died and this is not a very old box , maybe 1 year. There are three live wires from motor to controller. No ground from motor to controller and motor still runs at full speed.

 

Now the question is does the fact that the bed is hot an indication of something else?

Gerald,

Is this a 3 phase motor being ran on a phase converter?

If so check the impedance (ohms) between the three connections and the lathe bed on both the controller, and the motor with the power off. If one leg has a low reading compared to the other two I would suspect a short that is transmitting the voltage to the lathe bed.

Without knowing anything about the variable speed unit, I’m thinking the controller, and lathe should be grounded. Would certainly be mandated by code. I’m wondering if there is a short in the motor, and that is why the bed is hot, I have experienced this with a freezer unit that someone used without a grounded plug. Touch the freezer while touching the sink next to it, yell out in pain. Compressor worked fine until a ground was established, then instant short/tripped breaker. 94 volts is certainly enough to be lethal. In my head I can’t see how the voltage is getting to the bed, without a short, but electronics does strange things.

Don't forget to check the outlet.  Awhile back I got lazy and pinched a wirer just as it came into the metal box.  No issues for months.  But one afternoon when I touched a 7 ft piece of angle steel to the drill press and bandsaw sparks went flying.  

Larry it is three phase motor.

Thanks all for the ideas . We are talking about running a ground from lathe to controller. Should this ground possibly be direct from motor to another ground?

If the ground on the controller is good that will be fine to connect to.  I have a feeling when the controller was installed the ground to the motor was forgotten.  At least run a temporary piece of wire from a ground to the lathe bed and see what happens.   A high impedance digital voltmeter can give misleading readings.   Roly

Edited June 27, 20197 yr by Roly

Well he tried the ground idea with old extension cord. Cut the ends off and attach to motor and controller and no more shock. Also the motor is now working fine with the controller . He is now going to get a good 3 plus 1 wire and fix it proper. 

Thanks for the assist

I worked for a company that had VFD controller problems sending

voltage to the ground shocking people. They scraped the VFD's.

This was 3 phase to single phase machines.