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My grinder is zapping me, electrical advice needed.


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I have a Kalamazoo 2x48 grinder that I bought probably close to 15 years ago.  I've never had a problem with it in all that time, but lately I get a slight electrical shock when I touch any of the metal parts.

 

It has some damage to the power cord, sustained when I was dragging it out of storage in a tool shed several years ago, and the cord must have caught on something sharp.  On closer inspection today, the ground wire was cut almost completely through.  It actually broke the rest of the way when I was stripping some of the outer insulation off to look at it.

 

There's also enough damage to the negative wire that some bare copper is slightly exposed.  My theory is that power is arcing from the negative wire to the ground wire and electrifying the grinder, but I don't know much about electrical stuff, so if anybody out there does, I'd be glad to hear your input.

 

If I patch up the ground wire, will the problem be solved?  I hope it isn't something else, that will burn up the motor on me.  As much as I'd like an excuse to buy a 2x72, I don't want to part with the cash right now, and I need to keep grinding to help pay the bills.

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The first thing I would recommend is get a multimeter so you can test things without plugging it in and touching it. You don't need a $100 one one of the $20 ones will work fine for this. Could you send pictures of the exposed wiring as it sounds like it needs the power cord replaced which is depending on how its attached to the machine easy to do. I would recommend replacing the power cord and then testing the casing and motor leads with the multimeter to verify that was the problem.

 

I will always point out though that anytime you see damage on a power cord for anything you unplug it and inspect it immediately never put it off for years until it starts electrocuting you. 

 

If i'm interpreting this right then in the cut on the cord is where the neutral and ground wires are exposed correct? Not where it ties into the machine or elsewhere.

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Replace the whole cord if you can, it's usually not that hard to do.  I've done it by cutting the socket end off an old extension cord rated for the appropriate amperage and wiring it into the motor.  If you have a decent hardware store nearby, a length of 12/3 wire and a you-wire-it plug is even cheaper.  

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45 minutes ago, Sean Blum said:

The first thing I would recommend is get a multimeter so you can test things without plugging it in and touching it. You don't need a $100 one one of the $20 ones will work fine for this. Could you send pictures of the exposed wiring as it sounds like it needs the power cord replaced which is depending on how its attached to the machine easy to do. I would recommend replacing the power cord and then testing the casing and motor leads with the multimeter to verify that was the problem.

 

I will always point out though that anytime you see damage on a power cord for anything you unplug it and inspect it immediately never put it off for years until it starts electrocuting you. 

 

If i'm interpreting this right then in the cut on the cord is where the neutral and ground wires are exposed correct? Not where it ties into the machine or elsewhere.

 

Yeah, I feel pretty dumb saying "Hey, it still works" and forgetting about it for years.  I'm probably lucky it didn't start a fire.

 

You are correct about the cut in the cord.  I opened up the cover on the switch to see if anything was shorting out in there, but it all looked fine.  Nothing loose or corroded.  I'll put a multimeter on the shopping list.

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I have the same grinder.  I run into that issue whenever I am grinding on without touching the work rest.  My best guess is that the grounding in my shop wiring is faulty.  So with that as a starting point, you're pretty justified in thinking that the broken ground wire is the issue.

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So definitely fix the power cord no matter what. Alex I dont want to ask something that sounds dumb but are you sure its your wiring or are just building up a static charge using the grinder. I know with the grinders I use if I am in constant contact with the table(metal) or the tool rest Im fine but if I hover it will give me painful jolts everytime Im close enough. Grounding won't always get rid of the static so that's why I ask especially if you wear the right kind of shoes.

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I'll be honest Sean, no I'm not certain.  That theory was the result of a little bit of deductive reasoning, heavily influenced at the time by adult beverages.  Never really gave it much of a thought after that.  It sounds like you experience the same thing I do though, and the more I think about it the more sense that makes.

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Since most work shoes and really shoes in general have rubber soles it makes building up a charge really easy. Grinders are really just motorized rubbing a balloon across the carpet when it comes to static if you are insulated from the ground yourself. 

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My Grizzly with a ceramic platten and non-metallic casters will knock the crap out of you at certain times.

 

Usually when you're trying to lightly tweak the tip of a blade you've spent hours on with the steadiest hand possible.

 

Definitely static.

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Posted (edited)

 

37 minutes ago, Don Abbott said:

Definitely static.

 

I don't have a kalamazoo, but I get hit by significant static build up when grinding during dry spells as well. 

 

But if there's any bare wire showing in your power cord, you can't rule that out as the cause until it's replaced, and as you know, it should be replaced before plugging it in again, unless you have no concern for safety. 

Edited by billyO
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Even my KMG zaps me when it's really dry out and I'm wearing certain shoes.  As Sean said, a belt grinder is basically a Van de Graff generator and will generate all manner of static.  I've been known to wear a cable like computer repair guys do hooking me to the (well grounded!) grinder frame when it gets really bad, but my usual shop boots now have moderately conductive soles.  Look for anti-static soles on your shoes to keep that static zap down.

 

But, Billy is also right.  Any damage to a cord, especially if there is visible wiring, is an unsafe situation.  Static shocks can give you a good zap, say 10-20K volts, but it's an instantaneous burst.  A ground fault that uses you as the grounding path adds continuous amperage, and that is what will kill you. 115 volts at 20 amps will fry you like a sausage, where a 20,000 volt static bang will just make you jump.  

 

The mixed message here is that the same shoes that cause static zaps are generally insulating enough to prevent dangerous ground faults.  Generally.  And the ones that dissipate static will let you fry when hit with current.  The unmixed message is to make sure the cord and connections are in good shape so you don't have to worry about it. B)

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I've also heard of folks spraying their platen with static guard to mitigate the static shocks.  

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Thanks Alan my brain kept trying to tell me degaussing was the way to go and I had to keep reminding myself that's magnetism not static. 

 

There are like billyO a Alan said different ways to mitigate or prevent a static burst when using a belt grinder. How effective and worthwhile each one is is up to the end user. The key thing I would say other than always inspect your cords or any exposed wiring before you use them from plug to machine terminal is its worth it to keep a cheap multimeter around when you have electrical machinery especially as it ages or gets knocked around.

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My multimeter came in the mail yesterday.  I tried to test it for continuity, but the results were inconclusive.  I couldn't get continuity on any part of the ground wire.  Tried testing the plug to the cut end nearest to it, stripped to bare, clean wire.  Cleaned the plug down to bright metal also.  Then tested the other cut end to every part of the grinder that zapped me (the case and metal switch), and got nothing.  If I didn't know better, I would draw the conclusion that the ground wire doesn't conduct electricity at all.  A possibility more in the realm of reality, but still bizarre, is that the ground wire isn't connected on either end and the cut in the wire had nothing to do with it.

 

I thought I was doing it wrong or the multimeter was defective, so I read the manual again and tested it on some extension cords, and it worked fine.  Same results on the grinder. 

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So if it was zapping you enough that you noticed it but it was just kind of a oh that zapped me a bit the most likely it was static build up. If it was energized by the plug there will be no doubt in your mind its energized when it shocks you. Either way no matter what replace the cord then try retesting with a new cord. 

 

Its possible that the ground wire has multiple breaks in it did you test the positive and negative wires as well and get null?

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22 hours ago, Sean Blum said:

So if it was zapping you enough that you noticed it but it was just kind of a oh that zapped me a bit the most likely it was static build up. If it was energized by the plug there will be no doubt in your mind its energized when it shocks you. Either way no matter what replace the cord then try retesting with a new cord. 

 

Its possible that the ground wire has multiple breaks in it did you test the positive and negative wires as well and get null?

The first couple of times, it was just a strong tingle when I flipped the power switch, but then I got a zap from the case that was like touching an electric fence.  But I really hate getting zapped (from electric fence experience) so it's possible that I'm just sensitive to it and it was just static.  I tested the positive and negative against the case and ground wire and got nothing, so most likely it's not shorting out.  I'll replace the cord and see what happens.  They're cheaper than I thought they would be, so I should have just ordered one in the first place.  

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If its like a electric fence then more than likely it is being energized by the line. 

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