# LMS Sieg SC4 Popping My Ground Fault Interrupter



## CFLBob (Dec 30, 2019)

Maybe this is a problem that I'm the only person in the world has seen but with millions of SIEG lathes out there, maybe someone has seen it.

My big lathe is a Sieg SC4 bought as the Little Machine Shop 3540.  

I've been having issues with a ground fault interrupter in my shop popping for a while that are definitely not related to the lathe.   The lathe will be off and the GFI will turn off power.  The majority of that went away when the electric utility replaced a transformer, but it would still pop open every few weeks or go a couple of months.

Last week, I replaced the GFI outlet with a brand new one and then the weirdness started.  

Saturday, I turned on the lathe and was turning a piece at minimum speed (100 RPM).  I started running up the speed (RPMs) and popped the GFI.  I recreated that test three more times and every time the ground fault cut the power when I got above 150 RPMs.  I've run the lathe faster than that many times, on the GFI outlet that I replaced because I thought it might be bad.  

As a test, I put the possibly bad GFI back in the wall and put the new one aside.  Now I can run higher RPMs like I always did before.  

So I got a third GFI outlet (True Value hardware loves me).   Sure as can be, when I cranked up RPMs on the second NEW outlet, it also popped the GFI.   

Now I have two different, NEW, GFIs, that do the same thing.  I have one old GFI which doesn't pop at lathe settings that make the other two pop.  It's not really easy to make sense of that.  It seems to me that the lathe speed controller is probably doing something wrong during the transients while speeding up.

Anybody seen something like this?  

More importantly,  how do I fix this?  


Bob


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## WSMkid (Dec 30, 2019)

As a guy who has had gfi issues before (kitchen related) and seams to be a believer in doing the hard stuff first, check grounds. 

As a guess this issue started as soon as the lathe was bought and likely that circuit not used very much prior?

As a thought, garbage disposals and refrigerators are commonly ran on gfi circuits but they are not verible speed... do you happen to have a router with a speed control you can try on that circuit?

Do you have any other circuits (with or without gfi’s) you can try?

Have you considered a gfi breaker in the pannel vs an outlet?

Just some thoughts. 

GJ


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## CFLBob (Dec 30, 2019)

Thanks, GJ,

It's a long story.  The lathe has never popped a GFI before today and I've had it since 2015.  I replaced the outlet to try to fix the random power shut downs that have been happening since we built the addition my shop is in.   

Unless the lathe developed a problem in the last few days, it has never had problems.  The circuit is used very heavily.  My complete metal shop is pretty much all on it.  My variable speed mill doesn't affect the GFI, the variable speed lathe does.  My lower HP Sherline tools have never popped the GFI.  I run a computer on this circuit, my CNC control boxes, lights, a drill press, lots of tools.  

I do have a variable speed router I could use, not sure I could match the current consumption.  I could plug the lathe into another circuit with an extension cord, which doesn't have a GFI in line. 

Like I say, I have two different, brand new, GFI outlets, that do the same thing - they pop when I increase motor speed.  I have one four year old GFI outlet which doesn't pop at lathe settings that make the other two pop.


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## minh-thanh (Dec 31, 2019)

Hi CFLBob !
Maybe, Try replacing the power filter capacitor on the control circuit. when you increase the speed, the source will appear pulses (high and lot) capacitors can not filter that pulse and with the new GFI outlet (more precisely) will cause that phenomenon. !? maybe, when the frequency increases, the capacitor filter may leak current ..


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## TonyM (Dec 31, 2019)

Unshielded cable runs to and from frequency inverters  can set off  earth trips as they output non sinusoidal earth currents.

Make sure you use copper shielded cable from the mains supply to the speed controller and from the controller to the motor. (Steel armoured cables are not the same)
The cable should have an earth core included. Only connect the shielding to the earth at one end of the cable. The other end should not be connected. Some frequency converters have built in chokes but still advise shielded cables.


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## CFLBob (Dec 31, 2019)

TonyM said:


> Make sure you use copper shielded cable from the mains supply to the speed controller and from the controller to the motor. (Steel armoured cables are not the same)



The power lines aren't shielded at all.  This is an addition to our house we had built in '14 as planning for retirement.  The contractors hired electricians and they ran plastic jacketed cable (like Nomex brand).  

The LMS manual refers to it as a brushless motor, which implies the controller is probably a PWM controller varying the frequency to change speed.  I can see that might show up on the input if it's not well filtered.


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## dnalot (Dec 31, 2019)

My SX-3 mill pops the GFI when increasing the RPM, even though the mill is the only machine on the circuit (20Amp).  I finally just replaced the outlet with a non-GFI type. 

Mark T


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## WSMkid (Dec 31, 2019)

Is there a reason for that circuit to be gfi in the first place? Maybe it’s code? I’ve always lived in the country or in a town without codes so you could rig about anything you wanted. 

Do you have any other gfi circuits that you could swap the two new gfi’s into? I guess if it’s only your lathe that pops it then likely there is no reason for this...


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## werowance (Dec 31, 2019)

i had one doing that and it turned out to be a block heater on the generator.  was back feeding on the ground.  showed up a few months after several things got hit by lightning.   was putting something like 20 or 30 volts on the ground. and as soon as I would try to use a jig saw or anything on that outlet it would pop the gfi on it.  like to have never figured that one out until a friend came over and checked things out for me.  as a test you might try doing an isolated ground just for that one circuit.


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## CFLBob (Dec 31, 2019)

I isolated the ground pin with an adapter socket, (example) like you would use to plug a 3 pin grounded plug into a 2 pin outlet with a separate ground wire.  I could run it up to 250 or 300 RPM and it didn't pop the GFI, so that indicates the ground is getting some AC on it.  

Up above, I said,  "I could plug the lathe into another circuit with an extension cord, which doesn't have a GFI in line".  I did that a little while ago.  



WSMkid said:


> Is there a reason for that circuit to be gfi in the first place? Maybe it’s code?



I think it first got put in because it's code, but I'd like to keep it on that circuit because I use a Fogbuster (water-based) cooling on my mill that's also plugged into it.


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## werowance (Dec 31, 2019)

you isolated with an adapter socket but that didnt isolate the true ground on the outlet.  to isolate that you would unhook its ground and run a groundwire outside to a rod driven into the dirt and hook that to the back of the outlet for a quick test.  if it doesnt pop it on that one then you can use that same ground wire with a volt meter and touch one probe to the new isolated ground and the other probe to the suspected bad ground and see if you get voltage.  if you do then you know something is back feeding volts to that ground.  and since most grounds are common (meaning all ground wires are twisted together as 1 large common ground)  inside the breaker box that can be dificult or time consuming to locate which one is causing it.


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## werowance (Dec 31, 2019)

oh and on the note of testing the ground,  might be an easy check to verify that the contractor actually hooked those ground wires to a grounding source such as a grounding rod.  if its a steel frame building or old home i have seen where people never used a grounding rod, they grounded to iron water pipes and just to the steel frame of the building but never grounded those to a deeply driven into the earth grounding rod.  i recall as a kid our old home was water pipe grounded,  if you had so much as a cat scratch on your hand and you washed your hand you could feel a tingle.  that couldnt have been safe.


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## CFLBob (Dec 31, 2019)

werowance said:


> you isolated with an adapter socket but that didnt isolate the true ground on the outlet. to isolate that you would unhook its ground and run a groundwire outside to a rod driven into the dirt and hook that to the back of the outlet for a quick test. if it doesnt pop it on that one then you can use that same ground wire with a volt meter and touch one probe to the new isolated ground and the other probe to the suspected bad ground and see if you get voltage. if you do then you know something is back feeding volts to that ground. and since most grounds are common (meaning all ground wires are twisted together as 1 large common ground) inside the breaker box that can be dificult or time consuming to locate which one is causing it.



You're looking at it kind of backwards from what I was after - troubleshooting the wiring instead of the equipment.  My big question is "I have two possibilities: either the lathe or the GFI outlet is causing the problem - which is it?"  Seeing the 30 V of noise on the ground and that noise voltage goes up as RPM goes up tells me it's coming from the lathe.  I didn't learn anything about the house wiring.  

I didn't go into everything, but there is a house ground rod, 8' long, and I replaced the original about two years ago.  I have one of those three-light outlet checkers (like this) that tells me ground is good and the outlets are wired properly.  

Second biggest thing: I have two brand new GFI outlets that pop when the lathe goes over 150 RPM.  The old one I was using until I swapped them out doesn't trip.  Combine that with the noise on ground tells me the old one is bad.  

What I'd like to do is find out how to fix the speed controller on the lathe.  If there really is something wrong with it.


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## werowance (Dec 31, 2019)

Oh, sorry you are seeing 30 v on the ground when running the lathe but dont see it when not running the lathe?


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## CFLBob (Dec 31, 2019)

I'm a bit unsure of the 30V number and need to redo that, but yes.  There was noise on the ground pin that went away when the motor was off and the voltage went up as the I adjusted the motor speed up.

Normal life intervened a bit this afternoon and is taking some priority.  I might get back to it tomorrow.


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## Jasonb (Jan 1, 2020)

> Second biggest thing: I have two brand new GFI outlets that pop when the lathe goes over 150 RPM. The old one I was using until I swapped them out doesn't trip. Combine that with the noise on ground tells me the old one is bad.



Any chance the two new ones are a different current rating than the old one and being more sensative are nuisance tripping


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## TonyM (Jan 1, 2020)

CFLBob said:


> The power lines aren't shielded at all.  This is an addition to our house we had built in '14 as planning for retirement.  The contractors hired electricians and they ran plastic jacketed cable (like Nomex brand).
> 
> The LMS manual refers to it as a brushless motor, which implies the controller is probably a PWM controller varying the frequency to change speed.  I can see that might show up on the input if it's not well filtered.


Hi Bob. I was referring to the internal wiring from the outlet to the machine controller which needs to be shielded and linked to earth at one end.  I do not know what the codes are where you are from but do you have Type A and B trips. Type  A is for personal protection usually 5mA and suffers from nuisance tripping where DC drives are used and Type B for machinery usually 20mA up to 50mA.


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## CFLBob (Jan 1, 2020)

TonyM said:


> Hi Bob. I was referring to the internal wiring from the outlet to the machine controller which needs to be shielded and linked to earth at one end. I do not know what the codes are where you are from but do you have Type A and B trips. Type A is for personal protection usually 5mA and suffers from nuisance tripping where DC drives are used and Type B for machinery usually 20mA up to 50mA.



I figured you meant the power lines.   They are plastic insulated, no shielding at all.  The hardware stores I bought the GFCI outlets in are home improvement stores.  I'm sure they're the 5 mA kind.  



Jasonb said:


> Any chance the two new ones are a different current rating than the old one and being more sensative are nuisance tripping



The first one I bought was for a lower current rating, 15A instead of 20A.  The second one I bought was 20A.  They behave the same.  

The one I was replacing is 20A.


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## CFLBob (Jan 1, 2020)

I'm discussing this on another forum and somebody pointed out this quote from the LMS3540 product page on Little Machine Shop's web page   It's on the tab marked "Chris' Tips"

We have no expectation that any HiTorque machine will work on a circuit with a Ground-Fault Circuit Interrupter (GFCI). The National Electric Code has a specific exception to the requirement that receptacles in a garage or work area have GFCI: "_Exception No. 2: A single receptacle or a duplex receptacle for two appliances that, in normal use, is not easily moved from one place to another and that is cord-and-plug connected_".


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## jjr2001 (Jan 1, 2020)

Just some info here on my experience with the brushless motor mini lathe and mill.

My Micromark 7x16 worked fine for 3 years on my garage GFI. Then it started to on occasion trip it. Reset it and off she goes for hours or even days without tripping.
After about 6 months of this it just quit. Would not start at all.  The controller was fine...Motor  just quit. The windings showed signs of overheating and I think the insulation was breaking down.   No smell or burning.  The original motor was replaced with an external motor and VFD rated at 1hp. The VFD/new motor has never tripped the GFI and it has been running for over 1 year. 

I also have the Micromark mini mill and it runs on the same GFI circuit. It has also tripped the GFI but never quit.


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## CFLBob (Jan 1, 2020)

That's an interesting story!  I'm pretty sure the Micromark products are made by SIEG, too.  Probably similar motors and controllers - scaled to save a few pennies for the smaller ones (or made for the smaller and used on the bigger ones to save some money). 

My SC4 was five years old in December.  Due to some problems with fixing other things in the house, the last time I used it extensively was in the summer.  It's possible it's starting to go bad, but when plugged into a plain grounded outlet - like manual says - it seems to work fine.


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## jjr2001 (Jan 1, 2020)

Yes, I believe SIEG makes them under a lot of brand names. Great that it works on non GFI.
Cheers, JR


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## kf2qd (Jan 1, 2020)

You might try putting a couple of ferrite chokes on on the power cable. You are seeing induced noise on the ground wire.


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## awake (Jan 2, 2020)

CFLBob said:


> I'm discussing this on another forum and somebody pointed out this quote from the LMS3540 product page on Little Machine Shop's web page   It's on the tab marked "Chris' Tips"
> 
> We have no expectation that any HiTorque machine will work on a circuit with a Ground-Fault Circuit Interrupter (GFCI). The National Electric Code has a specific exception to the requirement that receptacles in a garage or work area have GFCI: "_Exception No. 2: A single receptacle or a duplex receptacle for two appliances that, in normal use, is not easily moved from one place to another and that is cord-and-plug connected_".



I think you just found your answer: apparently, Sieg has designed the PWM controller in such a way that it is electrically "noisy."

Which does and doesn't surprise me. When I blew the controller on my little 7x14 Grizzly, I did a good bit of tracking down and puzzling out of the controller circuit. It was pretty ... basic, shall we say. No isolation whatsoever, even/especially on the logic circuitry. The mains are rectified to DC - that part is not surprising. But then a resistor divider was used to generate the logic circuit voltage (!), and it did so on the high side of the DC rather than the low side. Thus, compared to the mains ground line, the logic ground was > 100v DC! Presumably their goal was to switch the N-FET on the high side rather than the low side. Ironically, the circuit used an opto-isolator to drive the FET, but that didn't actually do much isolating, since the logic circuit was tied directly into the high voltage DC.

I am not an expert with electronics, just an experienced hobbiest, but it all looked rather suspect to me, and I can imagine that it would lead to a very noisy circuit on whatever line it is plugged into. FWIW, I made my own controller, isolating the logic circuitry from the mains with a small transformer. For many years now it has performed flawlessly on the GFCI circuits in my garage. Of course, that might just be beginner's luck!

I could hope that the newer Sieg machines and their clones would be using a better controller than the original on my 7x14 ... but maybe not?


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## Wizard69 (Jan 3, 2020)

I just logged in and saw this thread.   

first off the behavior of GFI outlets do vary a bit based on the manufacture.  You could very well have a sensitive GFI.    I tend to doubt that at the moment based on other info in this thread.  

second if the GFI is protecting downstream outlets and you have stuff plugged into them then you really should unplug everything.   The problem here is that leakage currents add up, so every thing plugged in can potentially be leaking.   

some time ago I had real GFI issues and traced it down to a doggy extension cord.  Note that from the outside the cord looked practically brand new.  However it leaked in some manner and would trip GFIs.   At least I believe it was leakage the cord did not show signs of being shorted.  

The information that Little Machine Shop supplied is likely accurate.  It isn’t uncommon for noise mitigation techniques to leak current to ground.  This depends on the design of the electrical controls.  This is not a problem on equipment that is properly grounded.  However you need an outlet that isn’t GFI protected.


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## Ken I (Jan 3, 2020)

Just to throw an alternate hypothesis in here.
GFI's will trip on a neutral to earth leaks as well - neutral and earth are at approximately the same potential (theoretically - they never are because of volt drops) - so if you have a neutral to earth fault at your machine and you pull 1A on live then 0.5A goes back through the earth and 0.5A through the neutral - so the GFI "sees" an imbalance between live and neutral and trips.
Neutral to earth faults can normally be deduced because it doesn't matter what you switch on (on that circuit) it causes a trip.
But the fault may not be a dead short only a resistive fault and that will only trip when a certain load creates sufficient volt drop between earth and neutral (at the fault) to bring about the necessary current imbalance between live and neutral to cause the GFI to trip. And a highly resistive connection (like a wet fault) will need a much larger load to create the imbalance - so you might be working quite happily and someone elsewhere in the house turns on something and the trip occurs.

Bear in mind the fault can be anywhere in your system related to that GFI it doesn't have to be anywhere near the device that appears to "cause" the trip when it is switched on.

Neutral to earth faults can be very difficult to trace - my tip would be to disconnect all loads on the circuit - disconnect the neutral from the board and start hunting with a meggaohm meter.
With Neutral off the supply, the neutral line should be as clear of earth as the live line.

Once you have given your system the all clear - then start hunting for the same problems in all your appliances - and as Wizard69 pointed out an extension lead is an "appliance".

Also your neutral to earth voltage (under nominal current load) should never be more than a few volts - 30V is way too much and could be the result of a hot joint or undersized wiring for the load.
This might also be indicative an induced voltage in an earth loop.

A hot joint / wet wiring etc can all lead to GFI trips.

RF interference (from your invertor) can also induce currents in "Earth Loops" that might cause trips - try to avoid Earth Loops - all appliances must be earthed to a single earthing point in the board.

An example of an earth loop would be a lathe at one end of a steel bench and a mill at the other end - each with its own earth but also grounded to the common bench - thus the two earth leads and the bench form a loop - or an antenna for the RF to induce into.

If I get high spurious earth neural voltages I would normally slap on an oscilloscope to see what I'm dealing with - sometimes induced interference from inverters etc. causes harmonics which can also create havoc with GFI units. Cycling the various inverters up/down / on/off normally identifies the culprit.

Regards,   Ken


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## CFLBob (Jan 3, 2020)

Thank you @Ken I and @Wizard69.  The extension cord story is ... frightening, to be honest.  

The sum of the last few days is that I moved the lathe from the west outlets, which have a GFCI, over to the east group which doesn't.  The lathe is completely usable again.  The manual doesn't call out having a GFCI, just a grounded outlet, which it has.  

The lathe is just the latest episode of problems I've been having with the west branch throwing a ground fault and popping the interrupter.  The random GFCI popping goes back not quite as long as the life of the addition but almost as long.  I can't tell you how many times I've changed something and we've gone weeks without the thing popping and suddenly it does it again.  The reason I had replaced the GFCI when I stumbled across this problem was to try to fix random popping.  

Yesterday my wife was out there getting something and the GFCI popped while she was in the room.  There was nothing turned on or running at the time.  That's how it usually is when the GFCI pops.  Ordinarily, I go out first thing in morning and find it.  Sometimes it's not overnight, it just pops when no one is out there.  With the exception of last week, when I found I could make one pop deliberately, I think I've only seen it go twice since May of 2014 (when the addition was finished).  It has shut off my CNC equipment during a job exactly once.  Conveniently, I had just zeroed everything, so it didn't mess up any work. 

I've never bothered to write down all the things we've tried, but yesterday I had unplugged all but two things: a switched outlet with no surge protection in it (my CNC computer and big control box are switched by that) and a surge protected strip that has several low-current loads in it (my three Sherline DC motors, two CNC controller boxes, some lights, and an exercise bike).  All of that was off yesterday when it popped.  

A few years ago, when I found my house ground rod had corroded open and I put in a new one, I thought we were over the troubles.  Since then, I've done other tricks that seemed to make the problems go away; replacing the surge protected AC strips with unprotected ones, swapping the east side GFCI with the west side's one, other things I forget.  

So far the only thing I haven't tried is to unplug everything in the room when I'm not using it.  It would be a bit inconvenient to have to plug everything in every time I use it, but it might restore some of my vanishing sanity.  If it works.  

I suppose this is probably far enough topic off now to not belong here, since it's about my five year old problem and not the lathe, but suggestions are appreciated.


Bob


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## ignator (Jan 3, 2020)

Bob, your problems all sound like they are from the common mode EMI/EMC filters that are used to protect the electronics in your lathe, as well reduce RF emissions per FCC requirements. I could not find a schematic of the electronics for your lathe on line, but with a brushless motor, I suspect the input PI filter, where the capacitors are connected to ground, not neutral. Hence the requirement for a grounded outlet.
The other possible issue, your GFCI may be wired incorrectly, as I just found one, where the original electrician swapped wires from the input power to the protected outlets beyond, the neutrals were switched, and it randomly would trip. Easy to check this by looking at where the wires are in the bottom of the device box. 
Your computers have this same input PI filter arrangement. It all depends on the capacitor size on how much current is dumped at 60hz to ground, and if this is enough mismatch for the current transformer in the GFCI breaker to trip on.


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## CFLBob (Jan 3, 2020)

Thanks, ignator.  

I understand your point, but since it's all 120V single phase, the filter is probably on the side that's switched and not in-circuit to the GFCI.  When I replaced the interrupter outlet last week (three times), I verified the line and load connections to the outlet were proper by only wiring the line side and then turning the breaker back on to verify that voltage was on the outlet as it should be and the downstream outlets were off. 

I've resolved the question of the lathe by simply plugging it into the side of the room that doesn't have a GFCI.  We took that side's GFCI out years ago because we put in a freezer and had read about refrigerators and freezers causing them to pop.  

I think I'm going to adopt the habit of unplugging everything when I'm not using it.  That way if I go a long enough time, say until the summer thunderstorm season starts in May, without it popping, I can reason that it's either in the wiring or it's the power company's feed to us.


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## SailplaneDriver (Jan 3, 2020)

ignator has it right. It could be the filters in the drive. I'm a retired electrical engineer that specialized in power system anaylsis and protection. Here are some other things to keep in mind and things you may want to check:

- GFCIs in the US are designed to trip between 4 and 5 miliampers of current. It doesn't take much to cause one to trip.
- The GFCI measures what goes out the hot wire and compares it to what comes back through the neutral (white wire in US). The GFCI will trip f the difference is more than the 4 to 5 miliampere setting.
- A connection of the neutral to earth anywhere after the GFCI device can cause some neutral current to bypass the GFCI causing nuisance tripping. Isolate the neutral at the GFCI device and test for continuity to ground (will all devices unplugged from the circuit) to see it that is causing a problem.
- Conservatively, 100 feet of wiring at 120 volts 60 Hertz has enough capacitive leakage current to cause 5 miliampers of current through earth return. Much more than 100 feet and you are asking for trouble. This is a big issue for pools and the protection of underwater lights. It can also be an issue for extension cords.
- Most residences only have one GFCI that covers the garage, bathrooms and outdoor receptacles. The total wiring can be 100 feet or more and make the circuit prone to nuisance tripping.
- Moisture in an outdoor receptacle on the GFCI circuit can cause leakage that will make the GFCI circuit prone to nuisance tripping.
- Receptacle GFCIs have less wiring after the protection than circuit breaker type GFCIs. The less wiring makes the receptacle type GFCI less likely to nuisance trip. The receptacle type is also much less expensive.
- Noise filters connect to earth and will add to the normal wiring capacitive leakage current.
- Many plug strips include filters and will add leakage current. Too many devices with filters can make a GFCI prone to nuisance trip.
- The National Electrical Code (for the US) requires all circuits in the garage to be GFCI protected under 2020 Article 210.8(A)(2). There used to be an exception for dedicated appliances such as freezers and garage door openers but that appears to have been removed.
- Using an adapter to isolate the ground of the lathe, or any other load, is extremely hazardous. If the device shorts to ground you will become the return path to earth. Only do this for testing and be very careful. Test the frame of the device to earth to make sure it is not energized before touching. 
- GFCIs are electronic devices and will eventually fail. Test periodically to make sure they will trip. Use the test button on the unit. Better yet, get a receptacle tester with a ground fault test button on it and use that. This will not test if the device is too sensitive. It takes more specialized equipment to do so.
- Some GFCIs are sensitive to harmonics - the hash on the sine wave caused by electronics. 
- Some GFCIs are sensitive to the starting current of motors which may cause them to nuisance trip.

I don't know of a simple way to test the filters for leakage.  If you have a multimeter that can read AC amperes, you can make a cheater cord that will break out the earth return. Plug the lathe into the cheater and the other end into the mains receptacle. Run the cheater earth return through the meter and read how much current is returning to earth. If it is above 5 miliamperes, the problem is in the lathe somewhere - filters or some sort of short. If the current is well less than 5 miliamperes, the problem is elsewhere. If the current is above about 3 miliamperes, the combination of the lathe and leakage current from the wiring and other devices on the circuit is likely the issue.

GFCIs are simple devices and work well when properly installed and without excessive electronic devices plugged in. Check the above items to see if any of them could be the issue.


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## CFLBob (Jan 3, 2020)

As my profile says, I'm also a retired EE, but my specialty is radio frequency design: receivers, transmitters, PLL frequency synthesizers, feedback/control loops.  Anything in the DC to microwave spectrum.  Consequently, I understand how they're supposed to operate, what I don't have any feel for is how tolerant they are of things that designers didn't design specifically for.  In my last 20 years, I worked in commercial avionics.  Everything electronic for the big air transport airliners and the smaller business jets.  In aviation, everything is tested to major industry specifications so you know that nothing in the expected environment will cause the equipment to misbehave.  I know nothing about how GFCIs are certified but I bet they don't go to that level.   

At this point, I'm not thinking about the lathe, but about the fact that I've had random GFCI pops for over 5 years now and I'm about sick of it.  We have other GFCI outlets in the original house and a GFCI breaker in the house breaker panel.  None of those pop at all.  Ever.  (Except when we test them).  The one spot I'm fighting in the shop has never gone more than a couple of months without the GFCI popping.  The brand new 20A GFCI randomly popped yesterday.   

Virtually all of the hundreds of times that GFCI popped, everything in the shop was turned off.  As I said above, what made the lathe unusual was that I could make it fail just by increasing RPMs. 

About the "100 feet of wiring at 120 volts 60 Hertz has enough capacitive leakage current to cause 5 miliampers of current through earth return."   The shop is divided in half: east and west breakers.  The breaker box is connected to a GFCI at the first outlet, maybe 20 feet away, and that outlet protects the rest of the circuit.  From the breaker box to the last outlet is about 60 feet if you include going up into the attic and back down to the outlets.  This isn't just a straight series connection of 60 feet, it's some up, some down, some series and some parallel.  It's all "Romex" type, plastic-jacketed, three 14 AWG conductor wiring.  The west wall (the problem wall) also has an outdoor outlet, a branch of about 12' of extra wire.  

Both walls had the same arrangement, but I took out the one on the east side when we put the big freezer on it. 

Technically, I don't believe this is a garage.  Does that affect how the NEC considers it?  There's no space for cars, no doors big enough to allow a car in if I wanted one.  The contractor said we shouldn't call it a shop because that might bring county ordinances for workplaces into consideration.  It's a large, open space, 770 sq. ft.  It could have easily been more living space for the house with internal walls and (probably) plumbing.  

My inclination is to remove the outdoor outlet.  We were initially suspicious of it because of moisture, but there's no correlation of the GFCI popping after rain.  Went down that road years ago.


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## awake (Jan 3, 2020)

Oops, missed that detail in your profile (EE). I'm guessing you know way more about this stuff than some of us who have offered advice! Which makes your 5-year saga even more puzzling ...

Wish I had something useful to offer, butt I will certainly be interested to hear the details when you do figure it out!


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## CFLBob (Jan 3, 2020)

Well, for all the good it has done for me, the background doesn't matter.  

Troubleshooting intermittent failures is hard.  With radios we try to get them to fail constantly instead of intermittently.  If they fail cold, we spray them with refrigerants.  If they fail hot, we use heat guns (like paint peelers) and if they fail under vibration, I've been known to whack them with a rubber mallet.  

This system fails randomly at unpredictable intervals.  Like I say, I've only been in the room when it popped a few times.  There's probably a dozen things we did that were followed by not failing for a couple of months.  Now I think all of it was totally random.


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## SailplaneDriver (Jan 3, 2020)

Removing the outdoor receptacle is a good start. Do the continuity test to ground on the neutral wire. I've seen lots of problems in industry because of improper grounds on neutrals below the ground fault protective device. The same thing will happen to your GFCI if the neutral has an accidental earth downstream. Also check the earth return current on the lathe. That will pick up any problem in the lathe itself.

One of the guys I used to work with told a story of how he went to investigate some electrical switchgear that had burned down. He met the electrician on site. The electrician explained that this one circuit breaker kept nuisance tripping. The electrician had taken the cover off to obseve the operation of the breaker. Each time it tripped he saw a little lever jump up - so he wired the lever down. Turns out that there was an intermittent short circuit below the breaker. The electrician had disabled the trip unit by wiring the little lever down. The breaker overheated from the short and failed resulting in all the switchgear burning down. Sometimes when somethning trips it's trying to tell you something.


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## SailplaneDriver (Jan 3, 2020)

As to wheter your shop is a garage or not, if it is at or below grade and not intended as habital space, it has to have GFCI. See the snip of the 2020 NEC below. Depending upon when your shop was built, you may be grandfathered to an earlier edition of the Code and this requirement may not apply.


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## CFLBob (Jan 3, 2020)

SailplaneDriver said:


> As to wheter your shop is a garage or not, if it is at or below grade and not intended as habital space, it has to have GFCI. See the snip of the 2020 NEC below. Depending upon when your shop was built, you may be grandfathered to an earlier edition of the Code and this requirement may not apply.
> 
> View attachment 113152



Well, it's certainly an accessory building.  I'm not aware if the Powers That Be here require everything to be retrofitted when the NEC is revised.  I will have to talk to the building inspector's office.


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## SailplaneDriver (Jan 3, 2020)

CFLBob said:


> Well, it's certainly an accessory building.  I'm not aware if the Powers That Be here require everything to be retrofitted when the NEC is revised.  I will have to talk to the building inspector's office.



You are generally "grandfathered" and not normally required to update to current code unless you make changes. I would not bring it up to your building department since it could open a can of worms.

What year was your shop built and what city/state are you in? I can look up the code requirements at the time of construction.


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## CFLBob (Jan 3, 2020)

I'm pretty certain that the building doesn't have to meet the current code unless it has been modified and needs a new inspection.

The shop was built in 2014 and I'm in Melbourne, Florida. 



SailplaneDriver said:


> One of the guys I used to work with told a story of how he went to investigate some electrical switchgear that had burned down. He met the electrician on site. The electrician explained that this one circuit breaker kept nuisance tripping. The electrician had taken the cover off to obseve the operation of the breaker. Each time it tripped he saw a little lever jump up - so he wired the lever down.


That's mind-numbingly stupid for an electrician.  It would be pretty stupid for Joey Bagadonuts, random homeowner, but for someone who should understand why breakers are there...



SailplaneDriver said:


> Sometimes when something trips it's trying to tell you something.


That's always my assumption.  I've never replaced a fuse with a penny - or copper bar.


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## Ken I (Jan 4, 2020)

Sorry Bob - I also didn't see your bio EE - my apologies for teaching you to suck eggs (WRT to earth loops and RF interference).

I once had a problem which was ultimately traced to the nearby electrified railway having lost one of its local earth spikes due to corrosion. The system was thus grounding HT literally through the earth. Since it depended on how dry the ground was (seasonal) and how heavy the train was and whether it was accelerating or not as it passed by - it was an infrequent cause and not easily identifiable. Eventually we realized it mostly happened in the dry season and finally when a train was stopped by a red light and had to pull away again. The rail company fixed it as soon as we notified them that we thought they had a problem and GFI faults stopped.

As Sherlock Holmes says - when you have eliminated all possible causes, then only the impossible remain.

Good Hunting - Ken


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## CFLBob (Jan 4, 2020)

Again, no problem, Ken.  For all the good it has done for me, the engineering background is hardly worth mentioning.  

That ground issue you talk about is one of things I'm trying to figure out how to assess.  There are tracks about 6/10 of a mile from here, probably too far. 

Among the things that I've thought would have fixed it for good was when the power company replaced a transformer we share with three other families.  We have underground utilities here so it's not branches touching a wire and interrupting it.  We started to go through a period when the lights would dim or pulse in brightness and that was highly correlated with the GFCI popping.  We called it in and after some troubleshooting, the power company came out and did the replacement.  It was about two months before it popped again, and I really thought it was going to stay working until then.  

Maybe I should try some of the troubleshooting things I'm used to on the outlets.  Hit them with a heat gun and see if I can cause one to fail.  It has never correlated with cold, so freeze mist seems like the wrong direction.


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## MachineTom (Jan 4, 2020)

A ground fault interrupter was designed for Bathroom and kitchen use. All about moisture creating a path from hot to YOU.  If you have a motor with brushes, the carbon dust creates a leakage bridge to ground, or the metal dust in a non brush motor. Leave the GFI in the bathroom where it belongs.

So years ago i sold a TP grinder to a guy from our group. It worked fine for me for years. When he got it he called to tell  me the motor was shorted out. Wanted his money back. I asked him how it was hooked up, and he said through a GFI box. Lose the GFI box I told him. works perfect. now for years.


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## Fordgalaxy (Jan 4, 2020)

Most likely cause, you have the neutral and ground crossed at some point in that circuit.  Both the neutral and ground are connected to the ground bar, yes they go to the same place.  They create two paths to the same place, The neutral is the return path for the power, and the ground is for safety by providing a path of less resistance to ground than you do.  The neutral  is created in your breaker panel where the neutral bar is attached to the ground bar.  If they are crossed everything works fine, until something else on that circuit is used and even then a GFI may not trip, MMM intermittent pain in the butt troubleshooting.

Please don't heat gun your outlets, it won't help. 
Don't let Engineers trouble shoot, they're best left crunching numbers, and shouldn't be allowed to play with tools.
Sorry had to slip that in, dealt with a lot of engineers in my various adventures.

My qualifications Licensed Electrician.  Commercial/Industrial, and "The Guy".


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## CFLBob (Jan 4, 2020)

I spent enough years as an electronics production bench technician and then an engineering lab technician to think that doesn't apply.   

Whatever I have is intermittent, like once every couple of months.  I have one of those three light AC line checkers and it has never shown an issue, so it's not a permanent wiring error.   If it's an intermittent wiring error that shows up every few weeks or months (or every few hours when it feels like it) I suppose we'd have to be looking at the tester in the instant that it fails, and even then, if the GFCI trips in 1/30 second (2 cycles), humans can't see that.  1/30 of a second is a _long_ time to electronics but short to a person.  

So what do I do?  I've replaced the GFCI outlet three times.   I could fill a page with  all the other things I've done - taken out surge protected power strips, put in non-protected strips, put in different surge protected strips.  Left motors unplugged.   Do I replace all the outlets?  There's four of them.


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## Wizard69 (Jan 5, 2020)

It is possible that those surge protection strips are an issue.  It all depends upon how the MOV’s and gas tubes are wired up.  In most cases turning the strip off will not help.  I’d unplug that strip and not use it to see what happens over time. 

Also being that this is a garage I’d keep track of humidity, it is possible that a drastic change could put something that is leaky over the edge.  

also if the GFI protects outlast out side of the garage you probably should have those outlets looked at.    Rain or even bugs in the outlet box can cause a lot of strange issues.  

These are just a couple of ideas off the top of my head.   Can’t sleep at the moment so im only half here.  



CFLBob said:


> Thank you @Ken I and @Wizard69.  The extension cord story is ... frightening, to be honest.
> 
> The sum of the last few days is that I moved the lathe from the west outlets, which have a GFCI, over to the east group which doesn't.  The lathe is completely usable again.  The manual doesn't call out having a GFCI, just a grounded outlet, which it has.
> 
> ...


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## Wizard69 (Jan 5, 2020)

As for that outdoor outlet it isn’t just rain but bugs that can trip a GFI.  

The responses above are really good except for the comment about extension cords or power cords.   I’ve seen cords far shorter that 100 feet trips GFI, in at least one instance it was like new.   It appears that they fail via resistive leakage. In many cases the quality of extension cords and power cords is extremely poor. 

At work we have a very large number of PC’s wired to GFI outlets.  We actually have gone through a large number of these GFI outlets in the last year, they simply decided to give up at the same time.  However in a couple of cases the issue was corrected with new power cords to the PC’s.   The point is you can have multiple issues including bad GFIs.  There is a huge difference in the GFI outlets too, you basically get what you pay for.  

Your wiring and machines can be checked by an electrician that knows what he is doing (many don’t).  He would need a high voltage ohm meter or leakage detection equipment.  As do it’s above GFIs will trip when the current difference between hot and neutral exceeds a specific value (5milliamps in most cases).    That isn’t much current when you consider how much power your tools draw.  



CFLBob said:


> As my profile says, I'm also a retired EE, but my specialty is radio frequency design: receivers, transmitters, PLL frequency synthesizers, feedback/control loops.  Anything in the DC to microwave spectrum.  Consequently, I understand how they're supposed to operate, what I don't have any feel for is how tolerant they are of things that designers didn't design specifically for.  In my last 20 years, I worked in commercial avionics.  Everything electronic for the big air transport airliners and the smaller business jets.  In aviation, everything is tested to major industry specifications so you know that nothing in the expected environment will cause the equipment to misbehave.  I know nothing about how GFCIs are certified but I bet they don't go to that level.
> 
> At this point, I'm not thinking about the lathe, but about the fact that I've had random GFCI pops for over 5 years now and I'm about sick of it.  We have other GFCI outlets in the original house and a GFCI breaker in the house breaker panel.  None of those pop at all.  Ever.  (Except when we test them).  The one spot I'm fighting in the shop has never gone more than a couple of months without the GFCI popping.  The brand new 20A GFCI randomly popped yesterday.
> 
> ...


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## SailplaneDriver (Jan 5, 2020)

Wizard69 said:


> As for that outdoor outlet it isn’t just rain but bugs that can trip a GFI.
> 
> The responses above are really good except for the comment about extension cords or power cords.   I’ve seen cords far shorter that 100 feet trips GFI, in at least one instance it was like new.   It appears that they fail via resistive leakage. In many cases the quality of extension cords and power cords is extremely poor.



The 100 feet is total from the GFCI to all loads and includes the wiring inside the wall. Shorter extension cords can easily cause a nuisance trip. It all depends on the condition and design of the cord, and the amount of wiring in the walls.


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## CFLBob (Jan 5, 2020)

SailplaneDriver said:


> The 100 feet is total from the GFCI to all loads and includes the wiring inside the wall. Shorter extension cords can easily cause a nuisance trip. It all depends on the condition and design of the cord, and the amount of wiring in the walls.



What about the parallel or series connection aspect?  The outlets are in series where each hot or neutral goes to the next hot or neutral, and an extension cord on an outlet in the middle would look like a shunt (parallel) load.  Say there's two outlets, one 25' (total wiring up/down to the outlet) and one at 75'.  An extension cord in the first one acts like a parallel load while the same cord on the last outlet just looks like the load is farther away in series.  

Inductances (in the wire length) and capacitances between the wires behave entirely different in series vs. parallel.

By length alone, people shouldn't put a 50' extension cord in an outlet 75' feet away, but the same cord is fine in an outlet 25' away. 

Also:


Wizard69 said:


> Also being that this is a garage I’d keep track of humidity,



It's worse than that.  I'm in Florida.  Humidity is one of the state's major exports.  It's always humid, but sometimes are worse than others.  The shop is air conditioned, which means there's a humidity gradient from inside through the drywall and insulation, then the concrete blocks to the outside world.  Since it's about as cool as it gets around here, the shop air has been off pretty much since November.


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## SailplaneDriver (Jan 5, 2020)

CFLBob said:


> What about the parallel or series connection aspect?  The outlets are in series where each hot or neutral goes to the next hot or neutral, and an extension cord on an outlet in the middle would look like a shunt (parallel) load.  Say there's two outlets, one 25' (total wiring up/down to the outlet) and one at 75'.  An extension cord in the first one acts like a parallel load while the same cord on the last outlet just looks like the load is farther away in series.
> 
> Inductances (in the wire length) and capacitances between the wires behave entirely different in series vs. parallel.



All of the wire downstream of the GFCI will add capacitance. All of it is in parallel and will add since it is shunt capacitance.


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## SailplaneDriver (Jan 5, 2020)

An interesting item to note for those versed in electrical stuff, the leakage current from deteriorated or even normal insulation is resistive and is in quadrature (at a 90 degree angle) to the capacitive leakage current. They add at a 90 degree angle and not aritmetically. Not terribly useful but interesting.


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## CFLBob (Jan 5, 2020)

SailplaneDriver said:


> They add at a 90 degree angle and not aritmetically.



Yeah, that's my world.  At radio frequencies, resistors aren't, capacitors also have inductance and vice versa.  I wouldn't think of buying a calculator that can't do complex numbers.    

My new GFCI popped again this afternoon.  As usual there was nothing on in the shop and it popped at some time between when one or the other of us was out there for something so no one witnessed it.  This was two days since the last pop; the weather is drastically different.  Friday it was hot - set a record high of 86, I think.  Today was barely in the mid-60s.  Quite a bit cooler and drier today.  

I pulled the outside outlet and put a wire nut on each of the wires to keep them from finding each other.


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## Rich N (Jan 5, 2020)

Hi All.  First post here.  Love watching the progress on all the engines.  Very nice work that I hope to be able to do in the future.  As far as GFI's go I hate them.  First I must point out that where I live they are required if the floor is concrete, years ago I even had a CO inspector make me put them in a closed in carport that was asphalt.  I did see the post above about a dedicated outlet and he wasn't budging, I went there with him and he was a total you know what.

I would like to offer up the following that I have experience with when it comes to GFI's and house wiring problem just for consideration.

GFI's hate inductive loads.  Works today not tomorrow, or 5 minutes from now.
Capacitors start leaking the day they are born, and in the case of a variable speed drive that goes to DC bus, oh yeah check the input caps.
A faulty Neutral line on the utility input side at your house or the pole can cause this also. 
The line you are connected to has an outside outlet downstream that has moisture in it sometimes but not always would cause an intermittent problem also but not the problem you describe with the vari drive but definitely if your wife is in the shop and hears the click with nothing running.
We use many submersible pumps at work and they will work for a while on a GFI and then suddenly not, trips and will not work.  But plug them in on a non GFI and all good to go.

Perhaps you can insulate the floor around the machine and use the outlet with extension cord you mentioned earlier.  Good luck.


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## ignator (Jan 5, 2020)

CFLBob said:


> Yeah, that's my world.  At radio frequencies, resistors aren't, capacitors also have inductance and vice versa.  I wouldn't think of buying a calculator that can't do complex numbers.
> 
> My new GFCI popped again this afternoon.  As usual there was nothing on in the shop and it popped at some time between when one or the other of us was out there for something so no one witnessed it.  This was two days since the last pop; the weather is drastically different.  Friday it was hot - set a record high of 86, I think.  Today was barely in the mid-60s.  Quite a bit cooler and drier today.
> 
> I pulled the outside outlet and put a wire nut on each of the wires to keep them from finding each other.



Bob, it is possible that the NM wire has a leaking short problem that an Arc Fault Circuit Interrupter (AFCI) would trip on? I don't think the code requires these in a garage. And memory is post 2008 they (per NEC) became required for bedrooms, but now I believe all inhabited spaces in the home require these circuit breakers (NEC 2014). They look just like a GFCI in the panel, including a separate neutral wire. For laundry rooms, kitchens they require a dual GFCI and AFCI (all in one breaker).
My point is, there may be a nail or some other shorting in the wire down stream of your GFCI wall outlet NM wire that is causing all this. The arcing is intermittent. That's my theory. I've got these same GFCI's out in the garage (installed in the duplex receptacle boxes), and I've never had one trip. Most have ~30feet of NM wire to the protected down stream outlets.
Looks like your isolating the outside outlet. If it still trips, then you're going to have to figure out where the damaged wire is. I don't think the power company can produce problematic power that will trip the GFCI outlet.
I suggest at the first box with your new GFCI, take the source power re-connect to this GFCI, and to the wire running to the next box (i.e. make it a hot unprotected connection to the next box). At that box put in a new GFCI. I don't know how many duplex receptacles are chained to the first GFCI, but figure out what segment of NM cable has the problematic arc fault. (I know you are very capable of troubleshooting, but writing this for others, hopefully in a way that makes sense).
If you search the internet, you can find stories where electricians found nails and screws through the NM cable causing breaker tripping problems.


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## CFLBob (Jan 6, 2020)

ignator said:


> I suggest at the first box with your new GFCI, take the source power re-connect to this GFCI, and to the wire running to the next box (i.e. make it a hot unprotected connection to the next box). At that box put in a new GFCI. I don't know how many duplex receptacles are chained to the first GFCI, but figure out what segment of NM cable has the problematic arc fault. (I know you are very capable of troubleshooting, but writing this for others, hopefully in a way that makes sense).
> If you search the internet, you can find stories where electricians found nails and screws through the NM cable causing breaker tripping problems.



I removed the outdoor outlet yesterday, but the only reason I started there is because it's outside and we don't use it.  There was no evidence of insect life in the junction box, which is good, but I wasn't expecting it.  The wires looked slightly corroded, but since I haven't replaced a thousand outlets, I don't know if it looked normal for an outdoor outlet.  There's no particular reason to think that outlet is bad - or that any one of them is bad.

What this really comes down to is that after the box with the breakers on the south wall of the shop, I have four outlets and about 60' of wire.  I'll replace everything if it makes the problem go away.  

The nails or screws in the cable is the kind of thing I'm suspecting - either that or incomplete sealing around the wires allowing moisture into places it shouldn't be.


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## awake (Jan 6, 2020)

Bob, I think your and ignator's plan is a good one (rewiring so that instead of a series with one GFCI protecting all of the downstream plugs, each outlet has its own GFCI wired in parallel). At the very least, this may help to identify which section of wiring is causing the problems.

I don't think it really helps with your situation, but I have a set of dual outlets wired in two or three spots in my garage - by dual outlets, I mean two outlets side by side, one fed by one hot leg and the other by the other hot leg - effectively I have a 240v circuit across the hot wires of the two outlets, but each of them is returned through the neutral, so they are actually each just 120v circuits. But here's the kinky thing - they are wired with a common neutral and ground. Apparently this was acceptable in the code at the time (?) ... but it did not work with a pair of GFCI's in the first box wired to protect the downstream outlets; this arrangement kept popping the GFCI's. However, when the circuit was re-wired so that each set of outlets was made GFCI, wired in parallel rather than in series, all problems disappeared and it has been trouble free ever since.


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## CFLBob (Jan 6, 2020)

awake - I have nothing like that.  It's a plain old 120V single phase.  One pair (hot and neutral) coming in; one pair going out the GFCI has a labelled line and out and that's where they are.  The outlet closest to the breakers is the GFCI, and it's the only one.  The Line Out from the GFCI goes to three other outlets (or it did before I removed the one on the outside).  I've heard of multiple GFCIs on one circuit interacting before.


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## awake (Jan 6, 2020)

As I said, I figured that wouldn't help, but mentioned it just in case ...


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## CFLBob (Jan 7, 2020)

"This just in..."    

The GFCI popped late this afternoon, about 50 hours after I removed the outside outlet.  Nothing was on inside the shop.

I will leave it out, but I think tomorrow will bring a trip up to the hardware store to buy three outlets for the indoors and I'll change them all.   In the electrical technician world, this is called 'shotgunning' because you scatter your shots across the thing you're working on.  Any popping of the GFCI then means it's in the wiring.


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## Ken I (Jan 8, 2020)

Try switching off every load on that GFI circuit - if possible for some length of time. If possible physically disconnect all appliances - including their earths - completely unplugged.

Break the neutral and measure the current (unless you have a snap on that goes into mA territory). When removing the neutral from the board please remember to treat its open end as live - which it will be if the power is on and there is any live to neutral leakage or switched on load.

Run the live and neutral through a current transformer (it will only output the difference) and slap on an oscilloscope. Repeat on neutral and earth.

Repeat the above with appliances added incrementally.

Were into serious debugging here and you should feel right at home.

I'm beginning to think you may have some equipment (like an invertor) with filter caps connected to ground which when subject to spikes etc will effectively introduce a lagged load imbalance which may be unrelated to anything going on at your home - but mains disturbances elsewhere - like the earlier mention of dimming lights and problems with the pole transformer shared with your neighbours.

Regards,  Ken


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## CFLBob (Jan 8, 2020)

Ken I said:


> Try switching off every load on that GFI circuit - if possible for some length of time. If possible physically disconnect all appliances - including their earths - completely unplugged.
> 
> Break the neutral and measure the current (unless you have a snap on that goes into mA territory). When removing the neutral from the board please remember to treat its open end as live - which it will be if the power is on and there is any live to neutral leakage or switched on load.
> 
> ...



Thanks, Ken.  There are some useful concepts in there.  I can unplug everything; that's easy.  As you say, I may need to leave them unplugged for months.  I have had the GFCI go a couple of months without popping.  I suppose I would unplug everything I wasn't using, plug it in to use it, and unplug it when I'm done.  

My starting point is that there was nothing turned on at all on that circuit when it popped and there's usually nothing on when the GFCI pops.  Plugged into that branch was (1) a turned off Dell PC and monitor that I'm turning from a desktop into a doorstop, (2) a Belkin surge protected outlet strip with a bunch of things on it, all of them off; (3) a non-surge protected outlet strip with my CNC computer, monitor, Ethernet Smooth Stepper and CNC control box, all of them off and (4) the last outlet had my G0704 mill plugged into it, and turned off.  

I guess I should point out that all of the outlet strips have been changed at least once, and the Belkin one is a new one after swapping different strips in that spot.   

Since all of this is plain 120V single phase, I would not be surprised if things like my 4x6 bandsaw has the "bottom" end of the motor connected to neutral and the power switch just completes the circuit.  That's plugged into that Belkin strip.  

I have an AC milliameter and a clamp on, but I don't have a pre-made transformer I could measure with.  This sounds like the active part of a GFCI.  I do have some ferrite and iron powder cores I could wind one on, but is that something an electrician could buy?  I did a search of Grainger and a place called Westside (builder's supplies) and didn't get anything that I thought looked right.  


Bob


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## SailplaneDriver (Jan 8, 2020)

CFLBob said:


> I have an AC milliameter and a clamp on, but I don't have a pre-made transformer I could measure with.  This sounds like the active part of a GFCI.  I do have some ferrite and iron powder cores I could wind one on, but is that something an electrician could buy?  I did a search of Grainger and a place called Westside (builder's supplies) and didn't get anything that I thought looked right. Bob



Fluke as well as others make clamp-on style ground leakage detectors but they tend to be expensive.  You can get some cheap clones on FleaBay for a bit over $100 US.

Bob, you took out the original GFCI. You may be able to disassemble that one and remove the current transformer (CT) inside. You could put a resistor on the output of the CT and measure the voltage with an O-scope. Check the circuit board to see what size load resistor was used to prevent over burdening the CT. Never run a CT open circuit. It will saturate and put out a very high voltage impulse train since it is trying to act as a step-up transformer.


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## Ken I (Jan 9, 2020)

Ditto Sailplane driver's caution on open circuit CT's - normal practice  is to short the output when not in use. One of those rare occasions where it can literally burn out open circuit but is quite happy shorted.
So it needs a burden resistor for the test I was suggesting.
If you have a snap on you can do the neutral/live & neutral/earth checks with that. I have an AC/DC snap on "attachment" that plugs into a meter via banana plugs - it gives 1mV/A - handy for connecting the output to an oscilloscope.
I'd try exchanging the surge protected strip for a non-protected strip - those things often have filter caps, MOV's & GDT's transient surge tubes etc. down to earth.
Might be an idea to open it up / diagnose it.
These things are often rated for the degree of permited transient ie 300V, 400V & 500V for 120V outlets. Lower limits are good for protection but more prone to tripping.
The other thing you could try (if the strip is the problem) is to lift the ground end of the protection devices from earth and put them down to neutral instead - so the transient is more likely to ballance out at the GFI although phase shifts can still dick with it.
This modification obviously destroys the strips ability to protect you from a simultaneous rise in your live and neutral voltages relative to earth.
Perhaps you can re-engineer the strip to a low sensitivity to neutral (300V) and a much higher sensitivity (500-1000V) to earth.
The GFI trips might just be symptomatic of the strip actually doing its job and your problems are caused by a ratty supply - or something on your system (neighborhood / locale) is generating overvolt spikes which are being dragged down to earth by the strip.
Obviously if you have had equipment failures caused by overvolt transients - and that's why you installed a surge protection strip - then its doing its job - leave it in and live with the occasional trip or try and hunt down and kill the source of your tormentor.
Regards,  Ken


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## SpringHollow (Jan 9, 2020)

I do not know what you have plugged in but there are many things that still draw some power when "turned off".


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## bluejets (Jan 10, 2020)

SpringHollow said:


> I do not know what you have plugged in but there are many things that still draw some power when "turned off".



They don't "draw power".
What they do is provide a leakage path from the Neutral.
Which is why, as they have already stated, they have pulled the plug on all devices.

In my experience, there is usually one they miss somewhere such as a submersible septic pump or an added fault such as an outdoor outlets that has become a home for a million or so ants.
Even had it where ocean breezes blew up though the cavity walls and over the years created earth leakage paths in the outlets themselves.

Diagnosis can be troublesome at times even with the correct procedure, test instruments and the qualifications.


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## ccolby (Jan 10, 2020)

Your problem is the radio-interference reduction capacitors in the various components.  As they absorb from and release current into the circuit, they confuse the GFCI circuitry.  Vintage military-spec Porter-Cable portable belt sanders are the classic example in which the included instructions warned about this effect.  The only easy solution is to toss the GFCI and reinstall the less-intelligent receptacle and then don't do any machining while standing bare-foot in the water puddle on your basement floor.  You can Google all, of this.  That's how I learned about it after my surge-arresting outlet strip continually tripped the GFCI in my shop.


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## SpringHollow (Jan 11, 2020)

I was referring to some "power bricks" connected to equipment that is turned off, devices that have sensors always on checking for wireless remotes, etc.  They are consuming power/drawing current since they are not turned completely off even though the power switch on the device is turned off.  A television is a perfect example of this.


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## bluejets (Jan 11, 2020)

SpringHollow said:


> I was referring to some "power bricks" connected to equipment that is turned off, devices that have sensors always on checking for wireless remotes, etc.  They are consuming power/drawing current since they are not turned completely off even though the power switch on the device is turned off.  A television is a perfect example of this.



If the switch powering the "brick" is off then no current flows. (except the aforementioned leakage path through the Neutral.

What you are getting confused with is smps units in standby where power is still applied to the input and the smps generates a 5v dc standby voltage waiting for the press of a remote button or what have you to power up the main output.


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## SpringHollow (Jan 11, 2020)

I am not confused.  I understand what you are saying.  What I said was for those who turn off the power switch on a device and think it is off which is not totally true for some devices.  I was not referring to the plug strip power switch.  Earlier, it was said things were not turned on and that is why I said what I did.  I appreciate the effort you have put in to explain things.


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## CFLBob (Jan 11, 2020)

SpringHollow said:


> I am not confused. I understand what you are saying. What I said was for those who turn off the power switch on a device and think it is off which is not totally true for some devices. I was not referring to the plug strip power switch. Earlier, it was said things were not turned on and that is why I said what I did. I appreciate the effort you have put in to explain things.



And with no disrespect intended, the reason I didn't reply is that it's something I've known for about 50 years.  Even back then, there were "instant on" TVs that worked by leaving the tube filaments on all the time, so that when you turned on the switch they didn't take 20 or 30 seconds to warm up.  I'm well aware that the Dell computer that I'm cleaning up has a green LED shining off the back panel, even though they want us to believe it's off.  Something is obviously always on to power that LED.  

What you posted is good for someone who comes across this thread next month or next year that doesn't know these things, so it's valuable for other people.


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## CFLBob (Jan 11, 2020)

I came across something interesting while changing out all the outlets.  It just doesn't look like it should have been there.  







That's the neutral side.  Could that cause leakage current once every couple of months?  Or every couple of days if the conditions are just right?  (Just wrong?) 

I will continue the experiment of only plugging in the AC outlet strip that plugs into this outlet when I need to use it.  For a couple of months.


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## ignator (Feb 10, 2020)

Bob, any luck finding root cause of this tripping? Last post was a month ago.


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## CFLBob (Feb 10, 2020)

ignator said:


> Bob, any luck finding root cause of this tripping? Last post was a month ago.



Tomorrow will be four weeks since the last time it tripped.  It has gone longer without tripping and then started again, so I'm not convinced, but so far, so good.   To be honest, it will probably have to be six months before I start to believe it's fixed.


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## ignator (Feb 10, 2020)

Yes, the humid day's of summer yet to come.


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## SailplaneDriver (Feb 10, 2020)

If you just want info on how to troubleshoot GFCIs, skip down to the bullet list. 

I spent yesterday helpting a friend put in a transfer switch so he could power a subpanel from a generator during power outages. The generator itself has a GFCI. With the generator running and no load, we could plug the in the cable and everthing was fine. When we connected the cable to the transfer switch, again no load and the transfer switch on utility power, the generator's GFCI would trip. Testing of the cable and the transfer switch showed no problems. So I did what any safety concious person would do - I disabled the GFCI by disconnecting the shunt trip to the generator main breaker. This is NO a safety issue. I explain why not below.

The generator is 120/240v and has an internally grounded neutral. That is, the white wire (neutral) of the generator is connected to the green wire (ground or earth for you Europeans) and the generator chassis. The house is also 120/240V (obviously) and has its neutral grounded at the utility service (mains again for you Europeans). The cable which will connect the generator to the house is four-wire, two "hot" wires, one neutral wire and one ground wire. When the cable is connected from the generator to the house, there is a loop in the circuit created by the neutral and ground wires; the neutral is connected to ground at the generator and the neutral is connected to ground at the house. This loop is what is causing the generator GFCI to trip.

Modern GFCI electronic circuits have a self-check feature that is intended to confirm proper installation and proper opeartion after installation. One of these self-check tests if to determine if the neutral has been improperly earthed downstream of the GFCI. The GFCI puts a small pulse into the neutral and checks to see if it comes back through earth. That self-check feature is what was tripping the GFCI in the generator.

The above is why I have been repeatedly telling people who have GFCI nuiance trips  to check to see if the neutral has a ground downstream of the GFCI. This is a common causes of GFCI misoperation.

Now, why disconnecting the GFCI does not pose a safety hazard. The generator has no provisions for removing the ground to the neutral. The neutral to ground connection cannot be removed from the house electrical service since that would be a huge safety issue. Switching the neutral to the subpanel with a three-pole transfer switch that switches the neutral as well as the hot wires would work for most installation but not in this case; the homeowner has a battery backup system as well and a bypass from the main panel to the subpanel - don't ask why. Even if I could removed the internal ground from the generator, the GFCI only looks downstream of the ground location. In this case, the GFCI on the generator would only look INTO the generator and would not protect the cable or any other cords connected to the generator. There is no safety issue since the only load is the house wiring and it is already protected in accordance with safety standards. Additionally, I warned the homeowner not to use the receptacles on the generator without reconnecting the GFCI trip.

The moral of this story is check your neutral for grounds after the GFCI. Here are the other checks I recommend:

If the GFCI won’t reset, make sure that there isn’t an actual ground fault on the circuit.
Make sure the GFCI has been installed properly and is functioning properly.
Check if there is an outdoor receptacle on the same GFCI circuit. If so, check it for moisture and insects.
Unplug everything else from the GFCI protected circuit and see if the problem persists.
Don’t use plug strips with surge protection.
Don’t use extension cords.
There can be problems if there are too many receptacles on one GFCI. The total one-way wire connecting all the receptacles should not exceed 100 feet. That includes any cords plugged into the circuit.
Make sure the line and load wire on the GFCI are not reversed.

Have an electrician check to see if the wiring is proper at the GFCI and all downstream receptacles.
Make sure there isn’t another GFCI connected downstream of the one that is tripping. Connecting GFCIs in series can cause nuisance trips.
GFCIs can fail. Replace the GFCI.
If all else fails, install a dedicated circuit and dedicated GFCI for the device.

No, there is no exception for installing GFCIs in garages and shop areas. The exception was up until the 2005 edition of the National Electrical code. It was removed in 2008 and all subsequent editions.

No, I did not plagerise this from LMS - I sent it to LMS.

I am a licensed electrical engineer in California (previosly in several other states). I can provide my license number if you want to verify my credentials.


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