# Blows a breaker, what the heck??



## Mike8623 (Feb 14, 2019)

OK guys I bought this old 50's dumore tom thumb tool post grinder. Put it on my lathe and plugged it in and it propped a breaker. I reset the breaker took it off the lathe, plugged it in and it ran just fine. Every time I put it on the lathe and plug it in it blows the breaker. As long as I plug it in and don;t touch metal it runs just fine.........but if I touch it to metal it blows the breaker. Anyone have a solution or know what is wrong.


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## Latinrascalrg1 (Feb 14, 2019)

Sounds like you may have a short to ground situation when mounted on the machine.   Could be a cracked electrical cord insulation the leaks into the lathe like some sort of heat sink or maybe the way it's mounted is putting pressure  on an area that is causing the short inside or around that point.

Turn the lights off and try powering it in the pitch dark while you look for a flash.

I wasnt sure how those grinders were setup so i did a quick google search......if its similar to the ones i just seen then I would look very closely at the cord where it comes out of the grinder housing.


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## Technical Ted (Feb 14, 2019)

Does the grinder have a 3 pronged plug? If so, check to make sure the ground in connected.

Sounds like you have a short inside so you'll have to do some continuity checks and see what's going on. Chances are, if you were to touch something grounded and was holding on to the grinder without it attached to a machine, you would most likely get a shock!

I'd check things out before running it.

Ted


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## markba633csi (Feb 14, 2019)

Agree with all above- the fault lies with either the grinder OR the lathe. One of them has 120 volt leakage to the chassis and/or a poor ground situation.
Unplug the Dumore and test resistance of both prongs of the power cord to the metal housing using an ohmmeter- normally should read very high resistance, 500,000 ohms or more- likely this is where you will find a problem, if you have not been getting shocks from the lathe
Mark


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## Mike8623 (Feb 14, 2019)

the dumore has a cord that looks like the original one 60-70 years old and it looks it. I have not gotten any shocks from my lathe and I have been using it a lot lately. I did see a spark jump from the tool grinder to the lathe when I had the grinder plugged in and put it on the lathe and then as the grinder touched the lathe a spark and the circuit breaker popped.


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## Latinrascalrg1 (Feb 14, 2019)

If you have a scrap piece of rubber hose (tape or other cheap but appropriate material for this purpose) that you could slice open long wise to wrap around  the cord to insulate it for testing purposes  you will be able to verify the cord being the problem or not.
With that said the most likely  problem  area is probably gonna be right where the cord exits the housing.


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## tq60 (Feb 14, 2019)

Stop and check with volt meter.

To be safe do the following.

Get a cheap extension cord that is 2 prong not grounded.

Find a flat spot to work. Place newspaper on flat spot as insulator and plug grinder into cord while cord not plugged in.

Get a voltmeter.

Plug in cord and do NOT touch the grinder.

Measure voltage from grinder housing to the safety ground on the outlet. 

Should be zero if not be careful, unplug extension cord from outlet and look at which prong of the cord is in the smaller slot as this is the hot side. 

Flip plug over and plug it back in and repeat measurements.

Old equipment was not grounded and normal wiring is that the return connects to ground.

If there is a short from cord to case flipping the cord over stops the fuse blowing.

Stop now and open up the motor where the cord goes in.

Follow the wire that resulted in the voltage measured above and you may find it touching the case somewhere.

Once you figure out where the problem is then repair but that means new cord with a ground.

Good luck..



Sent from my SAMSUNG-SM-G930A using Tapatalk


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## markba633csi (Feb 14, 2019)

It could be a bad cord or it could be a short in the motor windings somewhere- sometimes hard to find- be careful
Mark


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## silence dogood (Feb 14, 2019)

After 60+ years rubber or plastic on cords gets brittle and break.  If you see cracks on the cord especially near where it goes into the motor or plug, replace.  On the 2 prong plug, were both prongs the same size (not good)?  If different, the bigger prong is neutral (wire should be white).  When you replace the cord make sure that the wire  (most cases black) is connected to the smaller prong side goes to the switch.  That is the hot side.  Best use a three wire and connect the green to the motor case.  Black wire will still go to the switch.  
The other thing is when you take the motor apart, check to see that there are no shorts from the motor wiring itself.  Since it is a tool post grinder, there could be some metal filings or dust. Brush off with a fine brush and spray with a electrical cleaner such as CRC.


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## Hawkeye (Feb 14, 2019)

For some reason, back in the days when they made tools and appliances with two-prong plugs, they made them with both prongs the same size. They then used the neutral wire as a ground, connecting it to the chassis. This meant you had a 50/50 chance of plugging it in with the chassis hot. Not a real problem until you touched the tool (or fridge, or whatever) and touched a properly grounded surface (like a stove or sink). Or, as in this case, the tool was actually touching the grounded surface (the lathe).

If that's the case, if you pull out the plug and turn it over before plugging it back in, then reset the breaker, it should work normally. If it does, unplug it and replace the old cord with a new, three-wire cord with the chassis connected to the real ground wire and the neutral NOT connected to the chassis.


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## BldrBill (Feb 14, 2019)

All it may take is holding the grinder in one hand and brushing against a grounded object (like the lathe) with your other hand, and you may be electrocuted.  Proceed with upmost care.


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## ThinWoodsman (Feb 15, 2019)

Mike8623 said:


> the dumore has a cord that looks like the original one 60-70 years old and it looks it.


Replace the cord! They're not expensive.
Also, take a look at the motor. Something that old which was likely sitting around collecting dust, there could be all sorts of debris in there causing a short in the windings. Maybe blow some compressed air in there.


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## markba633csi (Feb 15, 2019)

I don't agree with Hawkeye- I have never seen an appliance with one side of the power line connected directly to the case of the unit, by the factory. Even years ago they were smart enough not to do that, at least in the US
Mark
ps Can you imagine the lawsuits if there was a 50/50 chance of death every time you plugged it in?


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## Mike8623 (Feb 15, 2019)

OK guys, good news. I took the entire thing apart. I blew it all out and cleaned everything I could. I taped a few wires, that couldn't be replaced and put on a new cord. I then oiled it and put  a on/off switch in the cord. Plugged it in, turned on the switch and away she went, just like new, runs like a top.

I want to thank all that replied........you were a lot of help and inspiration, this is a great site, I always come here when  I'm stumped, now on to grinding my cutter box for my rifling machine build.


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## markba633csi (Feb 15, 2019)

Good deal Mike


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## Hawkeye (Feb 15, 2019)

Yeah, Mark. I know I wasted many years as an electrician. I only speak from experience. I try to avoid mere opinion. When I measure 90 VAC from the case of a fridge to the stove next to it, reverse the plug and measure 0 volts, I think that trumps what you have never heard about. I'm sorry I violated my own rule about not answering electrical questions.


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## higgite (Feb 16, 2019)

Hawkeye said:


> ... I'm sorry I violated my own rule about not answering electrical questions.


A good rule to live by. It has served me well.  

Tom


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## BldrBill (Feb 17, 2019)

Mike:  Make sure that you have tested the potential between the case and a ground with a voltmeter, then reverse the plug and check it again.

Reversing the plug on a device with measurable line voltage on the case just ties the case to the neutral (and grounded side of the circuit) instead of the hot lead, covering up the issue.  Plug it in backwards the next time, and the case once again will be hot.


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## markba633csi (Feb 18, 2019)

Hawk: I've encountered hot chassis but it's always been due to malfunction (leakage,or a stray strand of wire touching somewhere).  I've seen equipment (guitar amps, PA systems) with polarity switches that tie a cap from one side or other of the line to the chassis, for hum reduction. (also dangerous)
M
ps I believe my Dad had an old "all american 5" radio that had a hot chassis but it had a bakelite case and knobs, you weren't supposed to be able to touch the chassis during operation- I think he got shocked by it once replacing a tube


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## Hawkeye (Feb 18, 2019)

What I've always found odd is that the wall receptacles, while they didn't have a ground hole, did generally have the neutral slot wider than the hot. It would have been easy to provide the cords with matching plugs, but they chose not to.


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## Mark Needham (Feb 19, 2019)

*"Turn the lights off and try powering it in the pitch dark while you look for a flash. "*

If the breaker trips before you see a flash, put in a bigger breaker, until you get that flash. When the smoke comes out, grab it with a vacuum cleaner, and blow it up some ones bum.

Something bright and momentous, yellow or white, blue is good also. 
Just something going through my mind at the moment. Love it, Hey!


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## Blackjackjacques (Feb 20, 2019)

Mike8623 said:


> OK guys I bought this old 50's dumore tom thumb tool post grinder. Put it on my lathe and plugged it in and it propped a breaker. I reset the breaker took it off the lathe, plugged it in and it ran just fine. Every time I put it on the lathe and plug it in it blows the breaker. As long as I plug it in and don;t touch metal it runs just fine.........but if I touch it to metal it blows the breaker. Anyone have a solution or know what is wrong.



You don't say what breaker keeps popping - is it the lathe breaker or some other breaker?  However, I will ask a stupid question: Is the lathe fed from a GFCI breaker by any chance?


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## RJSakowski (Feb 20, 2019)

Hawkeye said:


> What I've always found odd is that the wall receptacles, while they didn't have a ground hole, did generally have the neutral slot wider than the hot. It would have been easy to provide the cords with matching plugs, but they chose not to.


Most of the newer two conductor plugs have one wider prong.   However, the neutral side of the line should never be belied upon for grounding.  Those tools and appliances which have a two prong plug are usually double insulated.


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## CluelessNewB (Feb 20, 2019)

Hawkeye said:


> What I've always found odd is that the wall receptacles, while they didn't have a ground hole, did generally have the neutral slot wider than the hot. It would have been easy to provide the cords with matching plugs, but they chose not to.



Unpolarized receptacles were still fairly common in houses in the US built before the early 1960s.  Many appliances had unpolarized plugs much later than that and some stuff like cheap Christmas lights from China still do.  I suspect the reason 2 wire unpolarized plugs survived so long was because of the old houses.   Personally I would never trust that a two prong polarized plug is wired correctly.   Actually I will take that one step further, I never trust that any old machine is wired correctly!  If the cord is worn, dry, crumbly or 2 wire it gets replaced with a new 3 wire cord.  If there is no provision for grounding, the frame gets grounded.


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## turnitupper (Feb 21, 2019)

Mark Needham said:


> *"Turn the lights off and try powering it in the pitch dark while you look for a flash. "*
> 
> If the breaker trips before you see a flash, put in a bigger breaker, until you get that flash. When the smoke comes out, grab it with a vacuum cleaner, and blow it up some ones bum.
> 
> ...


Was it THAT hot in Rocky on Tuesday, Mark?
John.


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## Hawkeye (Feb 22, 2019)

Thanks, Rich. That makes perfect sense.


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## BldrBill (Feb 22, 2019)

Bought a new portable vacuum cleaner which has a 35 ft long "California compatible" cord. Since they took the lead out of the plastic cord covers, extension cords are hard as a rock. Decided to buy a cord plug and receptacle so I can interrupt the cord, making it easier to coil over my hand and elbow, plus I’ll have a stand-alone extension cord if I need something in a pinch. The cheap pair I bought at the hardware store is polarized, as is the original plug on the vacuum. I’ll bet when most homeowners wire one of these up, or even wire up a new three prong plug, about 50% get the hot lead switched over to the neutral side. Double insulated appliances are a much better idea....


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## Mark Needham (Feb 22, 2019)

Low I sulation resistance


turnitupper said:


> Was it THAT hot in Rocky on Tuesday, Mark?
> John.


Hot, 'aint the word. 38C, with bloody high humidity. But, Yeah, I don't suffer fools, when it comes to electricity. But Darwin usually sorts 'em out.


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