Shocking experience with belt/disc sander

[Anthony Whitesell]

A few years back I purchased an old 9" disc/6"x48" belt sander. I don't know the year. I don't know the manufacturer, it might be a Craftsman. It is mounted on a post and belt drive.

I have been using it for a few years and either never noticed or was very lucky. Today while I was using I noticed I was being zapped. At first I thought it was static electricity, but it seemed too persistent. I took the voltmeter from the chassis to a ground output pin and was reading 120V. The plug appears original and not polarized. If I flip the plug 180 degrees, the problem goes away.

Why did it start happening now? Have I always been lucky and put the plug in the same way or is there something breaking? I took the area around the switch and capacitor apart, I don't see anything shorting to the chassis. I can't get a ohm reading (open circuit) from each plug pin to the chassis.

[Mike Henderson]

You definitely have a short from one line to the chassis. You really need to fix the short for safety. This is something I might do but I hesitate to recommend it. Connect the chassis to ground - a good ground. Then plug it in the way it was shocking you. The line will be shorted to ground and you may be able to see where it is burned.

Otherwise, while this is not the safest thing to do, you can put a polarized plug on the tool to make sure that the hot side is not the line shorted to the chassis. But you really need to fix the short.

Otherwise, dispose of the tool.

Mike

[The short probably developed recently. Could be a wire in the field of the motor is shorted to the housing. Vibration can wear through the insulation on those wires.]

[Anthony Whitesell]

I have not taken the motor apart. ALL the wires look to be in good repair. The voltmeter shows no continuity from the chassis to ground. I'm having the feeling your comment is the problem, it is in the motor and develops while it is running; a point in time when I cannot check continuity as there is voltage applied.

[Bill Dufour]

why can you feel it? what is the floor made of? If it is clean and dry you theoretically should not feel the voltage.
Bill

[Wade Lippman]

Oh, you would definitely feel a short off the hot side! There would be no reason for GFCIs otherwise.

I would just put a polarized plug on it. A short off the neutral is pretty much nothing; old dryers and stoves have the chassis connected to the neutrals and you can't measure any voltage off them unless the neutral is broken.

If it is something new, I wouldn't expect the tool to last much longer.

[Rod Sheridan]

I'm with Mike, I certainly would have the tool repaired or destroyed.

There's no sense having a fatality for the price of a sander.

The sander either needs to have the insulation resistance measured with a meg-ohmmeter, or it needs Hipot testing to locate the fault, and then be repaired. That said, I doubt that repair is economical when balanced against replacement costs.

Since it has a metal case it also should be modified to have a ground conductor if you solve the leakage to ground issue.

Do not continue to use the tool, your life is more valuable than that.........Rod.

[Bill Dufour]

[QUOTE=Wade Lippman;2683414]Oh, you would definitely feel a short off the hot side! There would be no reason for GFCIs otherwise.

I am not sure about that but I am not going to test my theory. Birds do fine sitting on a 12kv wire. I do not think they feel anything at all. but big birds can have wings long enough to touch two wires at once and then they fry.

The GFCI is only for a fault to GROUND, with no ground path no current to feel. I wonder if the concrete floor is damp? even so rubber shoes should insulate for only 120 volts. look how thin insulation is on a wire and that is good for 600 volts.
When i bought a used buzz box welder the plug was wired wrong. I could not get it to work because it was running on 120 volts instead of 240. turns out the case was hot at 120 volts. I never felt a tingle but the paint was good and I was lucky since I had it plugged into a dryer outlet next to my grounded washer and laundry sink.

[Steve Peterson]

I would troubleshoot the problem to determine if it is the motor or the wiring and fix it. The fact that it has a non-polarized plug indicates that the motor is really old. The wiring insulation back then would probably not be acceptable today. While you are at it, you may need to inspect and update both the motor and the wiring.

Steve

[Wade Lippman]

[QUOTE=Wade Lippman;2683414]

The GFCI is only for a fault to GROUND, with no ground path no current to feel. I wonder if the concrete floor is damp? even so rubber shoes should insulate for only 120 volts. look how thin insulation is on a wire and that is good for 600 volts.


If you touch a hot 120v there WILL be a ground fault; IIRC, GFCIs trip at 20ma, but you can feel 10ma. I have a tester that has a screw driver blade and a metal disk. You touch a suspected hot with the blade and the disk with your thumb; if there is 120v, a light will go on. It doesn't matter if you have rubber shoes on, the light will go on. It isn't enough to feel, so it must have a pretty big resister in, there is always some current.

I suspect one factor is that people are pretty big with a lot of surface area; however high the resistance/area is, there is a lot of area.

All I know for sure is that if you touch a hot you will get a shock; if you touch a neutral you won't, even if there is current on it (assuming it goes to ground!)

[Rollie Meyers]

A GFCI trips at 6ma, there are other specialty types that trip at 10ma.

[Mike Henderson]

I know I've tripped a GFCI by mistakenly touching a hot wire and I never felt a thing. All I knew is that the power on that line went off.

Mike

[Bill Dufour]

You know I have one of those neon light testers and you are correct it does not need to be earthed just my body is a big enough ground potential difference to light the bulb. I do remember as a kid pulling the plug from the wall on a toy train transformer. my fingers slipped forward and touched both prongs at the same time. I felt quite a tingle but it was all contained in my finger and did not go through my heart so i survived. I think wearing shoes and standing on dry concrete prevented current flow through my body and out my feet.