# Bench Grinder Tripping GFCI



## Nealtw (Jun 22, 2017)

l008com said:


> I have my grandfather's old bench grinder from the 80s. It's actually in really good shape, he died a few years after he bought it. Since then, over the years, my uncle and I would each use it occasionally in my grandmothers basement and thats it. I bought a house and took it home finally. I bolted it to my work bench and life was good. I sharpened a bunch of lawnmower blades this spring, it was really handy.
> 
> THENNNNN one day I plugged in the grinder and it instantly tripped the GFCI.
> Did it again, tripped it again. Tried a different outlet, it tripped THAT outlet.
> ...


The fabric covered wire looks like a soldered splice unwraped????


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## Windows on Wash (Aug 30, 2011)

If you don't see an obvious short, the capacitor might be fragged and require replacement. 

Usually you can see a bit of a bulge on that top of the capacitor that might indicate a failure in that case.


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## Nealtw (Jun 22, 2017)

If it is tripping with it in the off position. maybe replace or check the plug.


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## Windows on Wash (Aug 30, 2011)

Nealtw said:


> If it is tripping with it in the off position. maybe replace or check the plug.


Good catch. Didn't read that part of where it was tripping without it being even turned on. 

Probably a short in the plug or one of the wire attachments at that point.


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## 47_47 (Sep 11, 2007)

Check where the power cord goes through the grommet.


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## hkstroud (Mar 17, 2011)

Check the encircled area of power cord. Power cord looks like it could be rubbing against the capacitor bracket.


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## l008com (Mar 7, 2015)

Ok heres an update. I haven't taken anything apart yet, but I have taken a second look and a few more pictures.

First off, I figure it couldn't possibly be a capacitor issue, since it trips the breaker with the hard switch switched off, is this sound logic?

Second, the "solder" seen on the threaded wire is actually just the connector crimped on the end of the wire. It is all exposed but its not touching anything except the switch.

And the main power cord that comes into the base is really close to the capacitor/capacitor mount, but its not actually touching. And more importantly, the cable is MINT. Really everything is here. Nothing is worn out at all, nothing looks like it moves AT ALL.

I'll probably see if I can find a replacement on off switch first. It should be cheap and it seems like that's the only place the problem could be. There could be a short somewhere down the line, but like i said this power cord and really the whole machine was barely used and everything looks mint. I don't think there could be a short in the inner housing of the power cable, with the external housing in perfect condition.


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## l008com (Mar 7, 2015)

Oops I forgot the new pics:

Capacitor-Power Cable smooch:
https://i.imgur.com/uj5UVjW.jpg

Braided wire:
https://i.imgur.com/17qnXKB.jpg


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## chandler48 (Jun 5, 2017)

Not an absolute cure, but separate that green ground wire from the cap lug. If it is worn, there could be the answer. It could also be generating induced current from the cap wire to the grounding wire disturbing the balance in the GFCI. Just a stab in the dark, as it looks to be wired well.


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## hkstroud (Mar 17, 2011)

I would first disconnect the ground wire. If the GFI still trips that would tell you that the problem is internal to the motor or the wiring.
I would then disconnect the two leads to the switch. Then connect them together with a wire jumper. I GFI doesn't trip the problem is in the switch.


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## hkstroud (Mar 17, 2011)

I think first I would use my shop vacuum to vacuum the switch and then blow it out with compressed air (around the rocker part of the switch). This is a grinder, it makes lots of small metal filings.
I have to periodically do that to the switch of my wood router. It is mounted under a table and gets lots of saw dust in it.

I think I would bet a pizza that's the problem.


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## l008com (Mar 7, 2015)

hkstroud said:


> I would first disconnect the ground wire. If the GFI still trips that would tell you that the problem is internal to the motor or the wiring.
> I would then disconnect the two leads to the switch. Then connect them together with a wire jumper. I GFI doesn't trip the problem is in the switch.


Ok I disconnected the ground and the grinder didn't trip GFCI and it even ran.

I reconnected the ground and bypassed the switch and it tripped instantly. 

So you're thinking that means there's a short in the motor somewhere? Something like a loose wire i could fix? Or it is likely a fatal type of failure? Like the motor is fried?


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## hkstroud (Mar 17, 2011)

No, that indicates that something is shorting to ground, not something wrong internal to the motor. 

Disconnect the two wires on the switch then connect them together with a jumper wire. If GFI does not trip that will indicate that the short is in the switch. Probably metal filings in the switch. Have your tried blowing out the switch and vacuuming around the rocker arm of the switch?


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## l008com (Mar 7, 2015)

hkstroud said:


> No, that indicates that something is shorting to ground, not something wrong internal to the motor.
> 
> Disconnect the two wires on the switch then connect them together with a jumper wire. If GFI does not trip that will indicate that the short is in the switch. Probably metal filings in the switch. Have your tried blowing out the switch and vacuuming around the rocker arm of the switch?


I already tried that, that's what I meant by "i bypassed the switch". It still trips the GFCI as soon as you plug it in.


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## hkstroud (Mar 17, 2011)

> I already tried that, that's what I meant by "i bypassed the switch".


Sorry I missed that part. Show picture of where wiring enters motor.


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## l008com (Mar 7, 2015)

hkstroud said:


> Sorry I missed that part. Show picture of where wiring enters motor.


It looks like taking this thing apart enough to get to the motor is going to be kind of a big project. I haven't done it yet, I'll give it a shot when I have some spare time. 

Also do you owe me a pizza now? :biggrin2:


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## hkstroud (Mar 17, 2011)

Yes , I guess I do. What you want on it?


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## l008com (Mar 7, 2015)

hkstroud said:


> Yes , I guess I do. What you want on it?


Can I get a small half cheese, half working-bench-grinder....
hold the pizza.


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## hkstroud (Mar 17, 2011)

Why can't you show pic of top side of grinder? Have you been dribbling you cheese on it?


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## l008com (Mar 7, 2015)

hkstroud said:


> Why can't you show pic of top side of grinder? Have you been dribbling you cheese on it?


I'm confused, you want a picture of the outside top of the grinder? There's very little to see there at all. The cord goes in through the bottom, then from there, as pictured, up into the main case of the unit.


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## hkstroud (Mar 17, 2011)

So there is no accessible wiring connections, right?
Suggest you disconnect the motor leads Then remove base by removing those two nuts. You should then have access to the leads going into the motor itself. 
Test for short with ohm meter between each lead and frame. You should be able to insulate leads going into the motor with heat shrink tubing if test show a short.


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## hkstroud (Mar 17, 2011)

Also suggest, just to make sure that there is nothing screwy going on with the capacitor, remove the capacitor from its holding clip. Then plug in (making sure that capacitor is not touching frame) and see if GFI trips.


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## Nealtw (Jun 22, 2017)

The switch could be on the neutral so a short in the motor will still trip the gfci with the power off?????


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## l008com (Mar 7, 2015)

Waiiiiiit a minute. I was thinking about this the other day.

IF it trips the GFCI with the switch connected but off, and it trips the GCFI with the switch bypassed entirely, then doesn't that strongly suggest the problem is not in the motor, but BEFORE the switch? Which would basically mean in the cord. The cord looks fine but I'm told microscopic cracks in the rubber/plastic can leak enough power to trip GCFI?

And how do you re-cord something I've never done that before.


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## Nealtw (Jun 22, 2017)

l008com said:


> Waiiiiiit a minute. I was thinking about this the other day.
> 
> IF it trips the GFCI with the switch connected but off, and it trips the GCFI with the switch bypassed entirely, then doesn't that strongly suggest the problem is not in the motor, but BEFORE the switch? Which would basically mean in the cord. The cord looks fine but I'm told microscopic cracks in the rubber/plastic can leak enough power to trip GCFI?
> 
> And how do you re-cord something I've never done that before.


You could be right if you are sure the power is going down the cord and stopped at the switch. but if the plug is wired backwards the powers goes thru the motor and then stops at the switch.
Is the plug one that is easy to change, can you post a picture.


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## l008com (Mar 7, 2015)

Nealtw said:


> You could be right if you are sure the power is going down the cord and stopped at the switch. but if the plug is wired backwards the powers goes thru the motor and then stops at the switch.
> Is the plug one that is easy to change, can you post a picture.


Post #7 has a good pic: http://www.diychatroom.com/f29/bench-grinder-tripping-gfci-559850/#post4770562

I don't know for sure that the black is hot but it sure looks that way. And the plu doesn't look too hard to replace if I can find one just like it?


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## Nealtw (Jun 22, 2017)

l008com said:


> Post #7 has a good pic: http://www.diychatroom.com/f29/bench-grinder-tripping-gfci-559850/#post4770562
> 
> I don't know for sure that the black is hot but it sure looks that way. And the plu doesn't look too hard to replace if I can find one just like it?


The plug is the other end of the cord, and there are some junk that would be easy to have a problem with.

If the plug is not one that can be changed just undo the wires in post 7 and see if it still pops the gfci.


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## l008com (Mar 7, 2015)

Made some interesting progress tonight.

Based on what I thought was solid previous logic, I removed the power cord, safely isolated the conductors, and plugged the bare cord in. I knew the GFCI was going to trip. It did not DOH. But I am typing this right now, so I didn't kill myself and that's always good.

Then, while reassembling the whole thing, I found the friggin problem! 
One of the cloth covered wires was pinched bad between the main tube and the base! 

Here is the original photo I posted:









This photo ^ plus all the others I linked to, you can't see any problems. The problem is obscured in every picture. But a slightly different angle changes EVERYTHING!









It's connected to the red wire in the cord, which I would assume is the white wire in the wall, aka the neutral. So the neutral was grounded off the body of the unit. I'm not sure if I took the base off when I moved this to my house a year or so ago, so I don't know if this is something I did recently, or if it's something that happened 30 years ago and is just not getting bad enough to cause a problem. If I did it recently, I did still use it several times (sharpened three lawn mower blades on it this year) before it started tripping. 

Well now it's clear, I just have to replace that wire. This wasn't the job I wanted to do tonight, but oh well might as well get it over with, these things are very useful to have. So I take apart every screw there is, which leaves me with the picture below, but I still cannot get those end pieces off to get at the inside!










I tried and tried and tried, and eventually gave up. There was about 3/4" of wire out of the motor cavity before the kink. I'd like a lot more but that's what I had to work with. So I cleaned away the cloth (the the hell are there cloth covered wires anyway? Seems like an all-around bad idea, and they are a pain in the ass to work with.) Then I grabbed some spare wire out of my toolbox and I crimped it on at the break. Threw some heat shrink over it, threw some more over that, re-attatched all the wires, and BAM, it f'in works!










In the photo above, the white wire is the new one, replacing a cloth wire, and NOT pinched in the framework!

Here's video of it working again!





But there's just one problem. Watch that video a second time and keep an eye on the wooden box. Watch it walk around the table. Something I did put the thing way off balance. It vibrates the whole workbench now. I suppose I could have bent the "axle" when I had it resting on the 2x4's, but I wonder if it might just be that I somehow needed to 'balance' the grinding wheels a bit when I was installing them? I just took everything off then threw it all back on when I was done, I didn't see anything obvious that I missed so I'm not sure. But thinks jump right off the table now when it's running. It's still usable, it's not THAT bad, but it wasn't doing this back in the spring. Any thoughts on that?


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## SeniorSitizen (Sep 10, 2012)

Check the face and rim run-out of the stones. The flange washers can also be a contributing factor but usually to a lesser degree.


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