LMS Sieg SC4 Popping My Ground Fault Interrupter

[CFLBob]

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

 

[WSMkid]

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

 

[CFLBob]

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.

 

[minh-thanh]

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 ..

 

[TonyM]

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.

 

[CFLBob]

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.

 

[dnalot]

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

 

[WSMkid]

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...

 

[werowance]

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.

 

[CFLBob]

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.

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.

 

[werowance]

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.

 

[werowance]

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.

 

[CFLBob]

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.

 

[werowance]

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

 

[CFLBob]

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.

 

[Jasonb]

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

 

[TonyM]

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.

 

[CFLBob]

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.

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.

 

[CFLBob]

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".

 

[jjr2001]

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.