Strange Motor Problem Instantly Trips Breaker When Plugged In

[Maui]

I have a vintage 1/4 horsepower single phase motor that is used to power a Hook-Eye knife sharpener. The guy I bought it from told me that it doesn't work, but everything is there. It doesn't appear to be missing any parts, and the motor shaft turns freely. You can spin it with your fingers easily. When I plugged it in it with the switch in the "OFF" position it immediately tripped the in-line breaker on the outlet. I checked the connections between the power cord and switch, found a few loose connections, squared everything up, and the same thing still happened. I removed the power cord and switch that came with it and put them aside, and wired up a brand new power cord, plug and switch that I know is wired correctly and works properly - and I verified this with my ohm meter. Again, I plugged it in with the switch in the "OFF" position so there should not be a completed circuit, and it immediately tripped the breaker again. To make sure the outlet wasn't the problem I plugged my bench top drill press into the same outlet and when I turned it on it fired right up like normal. I checked for connections to ground from the common lead and the hot lead and found none.

I am truly puzzled. How can a motor trip the breaker with the properly wired switch turned OFF??

 

[MovingAlong]

How can a motor trip the breaker with the properly wired switch turned OFF??

Is this a GFCI breaker, Arc Fault, etc?

Have you removed the motor and just plugged the cord/switch into the wall? (careful with those live ends...)

Have you connected another motor to the same cord/switch and tested it?

 

[Gozo]

With the switch in the off position, essentially the hot goes nowhere, so nothing should happen. I’m guessing it’s a 3 prong grounded plug. If there’s a short from the neutral to ground AND the hot and neutral are switched, it’ll pop the breaker. Have you checked where each wire goes (and the frame) with a ohmmeter?

 

[Maui]

Is this a GFCI breaker, Arc Fault, etc?

Have you removed the motor and just plugged the cord/switch into the wall? (careful with those live ends...)

Have you connected another motor to the same cord/switch and tested it?

From my original post, I plugged my bench top drill press into the same outlet and turned it on. It ran perfectly, like it always does. So the outlet itself is not the problem. Yes, I used the power cord and switch (which I wired up) on several different motors. It works exactly as it should. I should mention that I have been rebuilding vintage motors for over a decade, and have never run into this problem before. When I replaced the original cord with the brand new cord and plug I got the same exact result.

 

[Maui]

With the switch in the off position, essentially the hot goes nowhere, so nothing should happen. I’m guessing it’s a 3 prong grounded plug. If there’s a short from the neutral to ground AND the hot and neutral are switched, it’ll pop the breaker. Have you checked where each wire goes (and the frame) with a ohmmeter?

Your first sentence I typed as bold because that was my expectation as well. Yes, it is a 3 prong grounded plug. Before posting this I checked for shorts from neutral to ground with an ohm meter and found none.

 

[cvairwerks]

Disconnect the load from the switch and try again. If it still trips, then probably a bad switch internally.

 

[Maui]

Disconnect the load from the switch and try again. If it still trips, then probably a bad switch internally.

I'm not quite sure what you mean here by "bad switch internally". Please clarify. I replaced the switch in the power cord with one that has been verified to work correctly, but it still tripped the breaker when plugged in with the switch in the "OFF" position.

 

[PCustoms]

Pictures?

What tripped, breaker, GFCI or arc fault? (Already asked but not answered)

What (with pics) wiring have you changed?

As already said, if you replaced the switch and it is off, then there is no current past that switch. The "breaker" should not trip

 

[Shoreline_]

Sounds like you have a grounded winding. Take a meter and check each lead to the case of the motor.

 

[PCustoms]

Sounds like you have a grounded winding. Take a meter and check each lead to the case of the motor.

Shouldn't matter if the switch is off though right?

 

[Maui]

Pictures?

What tripped, breaker, GFCI or arc fault? (Already asked but not answered)

What (with pics) wiring have you changed?

As already said, if you replaced the switch and it is off, then there is no current past that switch. The "breaker" should not trip

What would you want pictures of? Yes, I can upload photos of the motor and wiring. Do you want more than these?



The outlet breaker tripped as shown. The power cord, plug, and on/off switch have all been replaced with components wired by me that have been verified to work on other motors. I agree the breaker should not trip. But it does every single time the cord is plugged in with the switch off.

 

[PCustoms]

What would you want pictures of? Yes, I can upload photos of the motor and wiring. Do you want more than these?



The outlet breaker tripped as shown. The power cord, plug, and on/off switch have all been replaced with components wired by me that have been verified to work on other motors. I agree the breaker should not trip. But it does every single time the cord is plugged in with the switch off.

Ok, we're making progress.

You tripped the GFCI.

Your switch has nothing to do with the motor. Forget it for now.

Have you used a meter to check continuity on each terminal on the yellow wire, to the motor (ground) and to other terminals?

Pics of the motor wiring, where it connects to the yellow wire would be good.

 

[Maui]

Yes, I used the ohm meter to check for continuity on the plug that is wired onto on the yellow wire (which I wired up this morning) before connecting it to the motor as I normally do. After connecting the yellow cord to the motor I checked for continuity between the neutral and hot terminals and also checked to see if either the neutral or hot leads were shorted to ground. Neither showed continuity to ground.

 

[Cruzan80]

I sold my Hook Eye about a month ago, or would open it and check connections. For S&G, did you see if either screw terminal shows continuity with the shell of the motor?

 

[PCustoms]

For S&G, did you see if either screw terminal shows continuity with the shell of the motor?

If he checked at the plug he should have caught it, but can't hurt to double check.

He didn't check neutral to hot as far as I can tell.

He's leaking current somewhere. The fact that he does it with the switch plugged in but off is odd. I suspect something (possibly the outlet) is mis wired

 

[Cruzan80]

If he checked at the plug he should have caught it, but can't hurt to double check.

Hence the S&G part...

If it were me, I would confirm that the switch/plug doesnt trip the GFCI when disconnected from the grinder (sounds like it has worked previously on other stuff). If so, then the grinder is the known issue at that point. Remove the driven wheel and covers, and then diagnose where it is leaking internally and decide if worth fixing. Possibly, try hooking up to a non-GFCI to see if it is just enough to trip a GFCI, but not a normal breaker (and then make sure your meter is sensitive enough to pick up on that level of leakage).

Mine sold for $50-60 earlier this summer, and was listed for at least a couple weeks before someone bought it.

Edit: to help those who would otherwise search, it is *hits and giggles...

 

[Maui]

If he checked at the plug he should have caught it, but can't hurt to double check.

He didn't check neutral to hot as far as I can tell.

He's leaking current somewhere. The fact that he does it with the switch plugged in but off is odd. I suspect something (possibly the outlet) is mis wired

I did check neutral to hot as I stated in my previous posts. They show good continuity.

 

[Maui]

Hence the S&G part...

If it were me, I would confirm that the switch/plug doesnt trip the GFCI when disconnected from the grinder (sounds like it has worked previously on other stuff). If so, then the grinder is the known issue at that point. Remove the driven wheel and covers, and then diagnose where it is leaking internally and decide if worth fixing. Possibly, try hooking up to a non-GFCI to see if it is just enough to trip a GFCI, but not a normal breaker (and then make sure your meter is sensitive enough to pick up on that level of leakage).

Mine sold for $50-60 earlier this summer, and was listed for at least a couple weeks before someone bought it.

Edit: to help those who would otherwise search, it is *hits and giggles...

As I stated previously, I plugged my bench top drill press into the same outlet and turned it on. It ran perfectly as it always has. The breaker did not trip. Nor has the breaker tripped when I plugged anything else into the same outlet.

 

[larry4406]

Breaker is the device in the panel that energizes the entire circuit.

From prior post, you appear to be tripping the GFCI, not the breaker in the panel. Please confirm. If so, stop saying breaker tripped.

Different devices, different functions.

 

[Cruzan80]

As I stated previously, I plugged my bench top drill press into the same outlet and turned it on. It ran perfectly as it always has. The breaker did not trip. Nor has the breaker tripped when I plugged anything else into the same outlet.

This only tells me the outlet and breaker are good. My point is to take the switch and plug and make sure there is nothing between the grinder and the outlet that is bad.

The other part is plugging in the grinder into a non-GFCI, so you can tell if it is just enough to trip the GFCI outlet, or any breaker. As Larry just said above, you are mixing the term outlet and breaker in your posts so it isn't clear what is tripping.

If the plug/switch (without the grinder connected) do not trip the GFCI, then that part is good. After that, if the entire thing doesnt trip a non-GFCI, then the grinder has just enough leakage to trip the GFCI and you need to make sure your meter can read that sensitive. If the grinder trips a non-GFCI breaker, then it is definitely something inside the motor., and any meter should be able to sense the issue.

 

[Cruzan80]

I did check neutral to hot as I stated in my previous posts. They show good continuity.

If there is an imbalance in the hot going out and the neutral travelling back, the GFCI knows it has to go "somewhere" and trips. Continuity just means a path, doesnt do anything on imbalances.

 

[FrankLee]

Something amiss in the plug? Hot and neutral swapped? An errant strand sorting out in plug?

 

[PCustoms]

I did check neutral to hot as I stated in my previous posts.

Missed that, sorry.

Do you have an outlet tester?



I'm back to it trips the GFCI instantly with the switch (that works fine on other loads) off.

A GFCI trips when there is an imbalance of current. With the hot switched and the switch off you shouldn't have any current...

Something is backwards...

Take that for what it's worth. I've been cooking my brain doing concrete all morning.

 

[Maui]

I do not have an outlet tester, and since everything else I have plugged into that same outlet has worked fine with no problems, I do not believe the outlet is the source of the issue. One thing that comes to mind is this tool was designed for grinding steel knives, and it has no doubt generated a LOT of metallic grinding dust over the decades since it was put into use. Maybe that remnant dust is creating some sort of intermittent electrical pathway inside the motor at 120V allowing current to bleed from neutral to ground? Maybe a good cleaning could eliminate it? Time to tear into the motor and have a look...

 

[PCustoms]

@Maui for the hell of it, open your switch and show how it's wired.

The each end of that cord too if you're up for it

 

[signcrafter]

Plug it into a regular outlet that isn't gfi protected and see what happens.

 

[larry4406]

OP doesn’t seem to want to clarify GFCI trip vs breaker trip.

So, throwing darts at the wall…

 

[RTM]

Important thing to remember is that the GFCI tripping is much different than a breaker tripping.

The GFCI trips on a slight "leak of current" as an electrician friend called it. Been way too long since I was schooled on this by him, but assume a much lower bar than shorting things out. The recent note about dust etc could be on track.

If the new cord set and switch trip it without the grinder, I'd worry about your outlet dying. Over the years I've replaced several that would trip on one device, but not others.

Way too many comments coming in while I'm typing to keep up.

 

[whateg01]

How are you "checking continuity"? If you just have a meter that beeps when there's a short, you aren't going to see a high impedance somewhere. It'll just not be a dead short.

 

[whateg01]

OP doesn’t seem to want to clarify GFCI trip vs breaker trip.

So, throwing darts at the wall…

Op posted a pic of a GFCI receptacle that was lit up, I think indicating the GFCI was tripping, not the breaker.

 

[larry4406]

Op posted a pic of a GFCI receptacle that was lit up, I think indicating the GFCI was tripping, not the breaker.

Yet in subsequent posts he continues to say “breaker trips”….

I’m out. Good luck OP.

 

[mm08822]

Seems like ground and neutral may be rolled. Check if there is continuity from ground pin of plug to switch box and motor housing.

Check the same from neutral blade on plug.

(By plug, I mean the male cord end not the receptacle.)

 

[OccupantRJ]

Have you tried plugging this into a completely different circuit that is not on a GFCI?

 

[signcrafter]

What would you want pictures of? Yes, I can upload photos of the motor and wiring. Do you want more than these?



The outlet breaker tripped as shown. The power cord, plug, and on/off switch have all been replaced with components wired by me that have been verified to work on other motors. I agree the breaker should not trip. But it does every single time the cord is plugged in with the switch off.

Yet in subsequent posts he continues to say “breaker trips”….

I’m out. Good luck OP.

I'm guessing when he says "the outlet breaker tripped as shown" and showed a picture of the gfi that he is calling the gfi a outlet breaker. Using the wrong terms is causing the confusion.

 

[willf650]

I will point out something I have seen before. Those handy boxes are tiny so when I am ever using them for a device and not just a splice box I put the connectors in the ends and not the sides.


Those boxes are so small the metal connector coming in the side often will make contact with the wires/terminal on the device. I'm hoping this is not the case in your situation but have seen this in the field more than once.

No one notices this until it is energized.

Another thing I've seen with handy boxes many times is when coming in the ends with wires in a romex connector and you don't cut the device screws down in length they will pierce the wire entering the box.

I'm assuming one of these conditions may be your issue and your gfi is catching it before the breaker trips.

Obviously there is something up with your switch wiring.

I would take your switch set up out of the equation and plug your motor directly into the outlet to narrow down where your issue lies.

I will also point a meter will often not find an insulation issue due to only putting out a very marginal voltage. A megger will find something a meter will not but I think your issue is much simpler than that.

 

[Maui]

I will point out something I have seen before. Those handy boxes are tiny so when I am ever using them for a device and not just a splice box I put the connectors in the ends and not the sides.


Those boxes are so small the metal connector coming in the side often will make contact with the wires/terminal on the device. I'm hoping this is not the case in your situation but have seen this in the field more than once.

No one notices this until it is energized.

Another thing I've seen with handy boxes many times is when coming in the ends with wires in a romex connector and you don't cut the device screws down in length they will pierce the wire entering the box.

I'm assuming one of these conditions may be your issue and your gfi is catching it before the breaker trips.

Obviously there is something up with your switch wiring.

As it turns out I have another Hook-eye unit that I purchased several years ago. I just dug it out and even though it wasn't required, I used the same switched extension cord that I used previously with the other Hook-eye unit to plug in into the outlet. When I flipped the switch on the machine it sprang to life immediately with no issues. I turned it off and then turned it back on again. It ran again without any issues whatsoever. It is obvious that the motor on the other Hook-eye unit has some sort of electrical problem that has yet to be conclusively diagnosed.

 

[Cruzan80]

Given the second unit has a black wire coming out of the motor, it means that all you have identified is that from the white round plug onwards is good. Anything from the yellow prongs back on the first is suspect.

It could be the yellow cord is miswired, broken inside, or a bad connection inside the motor, or grinding dust, or... You need to take the meter out of continuity mode and start checking for resistance, etc, just like you would on any other given suspect motor.

 

[FrankLee]

Something amiss in the plug? Hot and neutral swapped? An errant strand sorting out in plug?

Open up the plug and verify the wire/cord did not get pulled out or twisted. Verify that hot and neutral are in the correct pole.

Pass & Seymour plug

 

[Maui]

I'm guessing when he says "the outlet breaker tripped as shown" and showed a picture of the gfi that he is calling the gfi a outlet breaker. Using the wrong terms is causing the confusion.

You are correct. Please pardon me for using the wrong terminology. The breaker located in the breaker box did not trip. The GFCI tripped. I have not tried plugging the faulty unit into another outlet yet. I'm going to open the motor up and have a look inside before doing that.

 

[PCustoms]

Can someone explain how, with his switch OFF, it's still tripping the GFCI?