LMS Sieg SC4 Popping My Ground Fault Interrupter

[MachineTom]

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.

 

[Fordgalaxy]

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".

 

[CFLBob]

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.

 

[Wizard69]

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.

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

 

[Wizard69]

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.

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.

 

[SailplaneDriver]

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.

 

[CFLBob]

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:

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.

 

[SailplaneDriver]

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.

 

[SailplaneDriver]

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.

 

[CFLBob]

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.

 

[Rich N]

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.

 

[ignator]

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.

 

[CFLBob]

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.

 

[awake]

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.

 

[CFLBob]

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.

 

[awake]

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

 

[CFLBob]

"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.

 

[Ken I]

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

 

[CFLBob]

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

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

 

[SailplaneDriver]

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.