# Strange Problem with Sieg SC4 (LMS 3540) and Ground Fault Outlet



## MontanaAardvark (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.  I was hoping to make that random power outage go away.  

Saturday, I turned on the lathe and was turning a piece at minimum speed (100 RPM).  I started running up the speed (RPM) 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 RPM.  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 are different brands, 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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## JimDawson (Dec 30, 2019)

I have seen similar problems with GFIs.  They work great with light bulbs and double insulated power tools.  But don't work well with electric heaters for instance (like in a control panel).  Not really tried one on something like a small lathe or mill.  There is apparently enough ground leakage in the motor/control circuit to trip the GFI.  I would just install a properly grounded non-GFI outlet for the lathe and be done with the problem..... unless your lathe is in a wet location.


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## MontanaAardvark (Dec 30, 2019)

JimDawson said:


> I would just install a properly grounded non-GFI outlet for the lathe and be done with the problem..... unless your lathe is in a wet location.



Thanks, Jim!

That properly grounded non-GFI outlet is available already, I just move my extension cord from five feet to the left over to five feet to the right.  It's as close to zero effort as there is.    

Ground leakage brings to mind something I've done in electronics test.  There are adapters that you plug a three prong power cord into and it isolates the ground.  They were for plugging three prong cords into the old two prong outlets.  If the cause is the motor controller leaking current onto ground, that will stop the GFI from popping.


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## JimDawson (Dec 30, 2019)

MontanaAardvark said:


> Ground leakage brings to mind something I've done in electronics test. There are adapters that you plug a three prong power cord into and it isolates the ground. They were for plugging three prong cords into the old two prong outlets. If the cause is the motor controller leaking current onto ground, that will stop the GFI from popping.



Yup, I've done that to ''isolate'' a scope ground, back in the day anyway.  Not exactly safe.  Today I use a proper isolation transformer, or a battery scope.

You might try the 2 prong test and measure the motor frame to ground voltage, maybe across a series light bulb to load it a bit.  Might be interesting to see what the leakage is.


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## Nigel123 (Dec 30, 2019)

Just another theory on this
Ground faults in Canada also trip on uneven current on the hot and neutral
A few milliamps will trip it depending on the sensitivity of the device
It measures the difference between the two wires
So if it trips with no ground prong the problem is with the lathe control
When it tripped when not running is the power disconnected from the lathe
either switch double pole or unplugged


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## MontanaAardvark (Dec 30, 2019)

Nigel,  I think that's how they work.  They measure the current in hot and neutral and I think they're set to open if the difference is more than .005 Amp. 

What you're describing about the lathe motor controller unbalancing hot and neutral a little is what I've been thinking is happening.  



Nigel123 said:


> When it tripped when not running is the power disconnected from the lathe
> either switch double pole or unplugged



It is always just switched off at the AC power switch on the lathe.  Since it's 120V, single phase, I always assumed, just the hot wire is switched.


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## Nigel123 (Dec 30, 2019)

Depending on the controller you have if the switch is double or single pole
Is the lathe plugged in to a receptacle or hard wired
If It doesnt trip when unplugged then the problem is more than likely in the controller
Not familiar with your lathe
Is It DC voltage maybe brush leakage but without it running not likely
Some motors here are exempt from GFI Sump pumps fridges deep freezers
Sorry my mix up the above motors are arc fault exempt not GFI


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## mksj (Dec 31, 2019)

With VFDs, it is a common occurrence to trip GFI's. You need expensive industrial GFI's which have a higher trip threshold (seem to recall it is around 25-30mA as opposed to 5mA).  Not sure on DC drives if that is what you have, but if it generates a lot of electrical noise it can be leak into the power wires and trip the GFI. I would not eliminate the ground connection, see comment below. Why not just put in a regular socket and skip the GFI, just put it back in if you decide to sell the house. I have had a number of intermittent GFI sockets that just seemed to go bad and trip erratically, I did have better longevity using a heavy duty 20A industrial socket GFI type. I also use several layers of surge protection starting at the service entrance, and at the sub panel.

Interesting comment I read on GFI's as to function and reliability "In addition, GFCI protection devices fail at times, leaving the switching contacts closed and allowing the device to continue to provide power without protection. According to a 1999 study by the American Society of Home Inspectors, 21% of GFCI circuit breakers and 19% of GFCI receptacles inspected didn't provide protection, leaving the energized circuit unprotected. In most cases, damage to the internal transient voltage surge protectors (metal-oxide varistors) that protect the GFCI sensing circuit were responsible for the failures of the protection devices. In areas of high lightning activity, such as southwest Florida, the failure rate for GFCI circuit breakers and receptacles was over 50%!"


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## Nigel123 (Dec 31, 2019)

mksj said:


> With VFDs, it is a common occurrence to trip GFI's. You need expensive industrial GFI's which have a higher trip threshold (seem to recall it is around 25-30mA as opposed to 5mA).  Not sure on DC drives if that is what you have, but if it generates a lot of electrical noise it can be leak into the power wires and trip the GFI. I would not eliminate the ground connection, see comment below. Why not just put in a regular socket and skip the GFI, just put it back in if you decide to sell the house. I have had a number of intermittent GFI sockets that just seemed to go bad and trip erratically, I did have better longevity using a heavy duty 20A industrial socket GFI type. I also use several layers of surge protection starting at the service entrance, and at the sub panel.
> 
> Interesting comment I read on GFI's as to function and reliability "In addition, GFCI protection devices fail at times, leaving the switching contacts closed and allowing the device to continue to provide power without protection. According to a 1999 study by the American Society of Home Inspectors, 21% of GFCI circuit breakers and 19% of GFCI receptacles inspected didn't provide protection, leaving the energized circuit unprotected. In most cases, damage to the internal transient voltage surge protectors (metal-oxide varistors) that protect the GFCI sensing circuit were responsible for the failures of the protection devices. In areas of high lightning activity, such as southwest Florida, the failure rate for GFCI circuit breakers and receptacles was over 50%!"



Very good information
The GFI instructions use to read test monthly
I for one are guilty of not doing that
I run many DC motors on my tools they can build up with
brush(carbon) dust which tracks to ground
It has not been a problem but I dont use GFI in the shop
I always use a grounded plug or connection
Does the Lathe stipulate must be GFI protected


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## MontanaAardvark (Dec 31, 2019)

These are excellent remarks.  I don't know what kind of motor is in the lathe; my guess it's "whatever is cheapest" in China.  The manual says "Brushless motor" which implies the controller is varying the frequency applied to the motor and not varying voltage.  Probably a cheap PWM controller.  

At the risk of too much information, this is in an addition to our house we has built back in '14 as planning for retirement.  We have two 20 A breakers in the wall with two rows of outlets which go down the east and west walls.  The west wall has all of my shop equipment on it: Grizzly G0704, Sherline mill and two Sherline lathes, a drill press, and everything except a computer, and three CNC control boxes all have motors.  I've used a bunch of handheld power tools: pad sanders, jigsaws, belt sanders, wall powered handheld drills...  Never seen this problem.  The Sherlines are all DC motors.  I think the Grizzly mill is a DC motor as well.  After resetting the GFI, I tested the mill's variable speed motor and the GFI didn't pop.

The west wall has had the GFI popping since we got settled into the shop.  The East wall hardly ever popped.  It has a larger freezer on it, and when we learned that refrigerators and freezers don't mix well with GFI outlets, I took the East wall's GFI out and swapped it with the one in the west wall.  The whole reason I decided to swap this GFI for a new one is to address its popping at random.  Sometimes it's twice in a day, sometimes it will go a month without it. 

I have a Fogbuster, water-based coolant on the mill but never on the lathe.  The lathe's manual says just to use a grounded outlet, nothing about using a GFI.


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## pontiac428 (Dec 31, 2019)

GFI is part of the electrical code, unfortunately.  I'm at the electrical phase of my shop building, and the electrician I hired to do my panel connection is the local community college instructor for electrical code.  He taught me a few things while I helped him pull wire about GFI.  A GFI breaker is the best way to go, but they cost $70 each, so that's a grand on breakers right there.  For $20 per circuit, you can use a standard breaker and run a single heavy duty GFI outlet first in line in series with cheap, regular grounded outlets.  It isn't necessary to have a GFI outlet on every receptacle.  You can use the money saved ($50 per circuit!) for something else that you actually want in your shop.  That may help with the number of senseless GFI trips.  For the record, I hate GFI outlets.  My Oster beard trimmer tripped the one in my bathroom three times the other day, and that's a 20 watt double-insulated power tool.


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## MontanaAardvark (Dec 31, 2019)

pontiac428 said:


> For $20 per circuit, you can use a standard breaker and run a single heavy duty GFI outlet first in line in series with cheap, regular grounded outlets. It isn't necessary to have a GFI outlet on every receptacle.



That's exactly how they wired my shop.  

I have other GFI outlets in my house, and a GFI breaker in the breaker box.  The one on the west wall of my shop is the only one that goes off randomly.  That's why I tried replacing it and ran into this issue with the brand new GFI outlets getting tripped by my lathe, but the old one that was installed in '14 doesn't get tripped.


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## DavidR8 (Dec 31, 2019)

MontanaAardvark said:


> These are excellent remarks. I don't know what kind of motor is in the lathe; my guess it's "whatever is cheapest" in China. The manual says "Brushless motor" which implies the controller is varying the frequency applied to the motor and not varying voltage. Probably a cheap PWM controller.



I would double check to see if the motor is truly brushless. My 7x14 was advertised as having a brushless motor but actually has a brushed motor. 
I have no idea if a brushed motor would leak voltage to ground. 


Sent from my iPhone using Tapatalk


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## Meta Key (Dec 31, 2019)

I wasn't familiar with Sieg machine tools (sounded vaguely European) so I went to the LMS web site to take a look.

3540 lathe at LMS

I was reading about the machine and clicked on the tab for "Chris' Tips" where I read:  

"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_"."

MK


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## MontanaAardvark (Dec 31, 2019)

Thanks for that Meta Key.  

I go to the lathe's product pages so often that I think I've memorized them, but obviously not.  I think "_not easily moved from one place to another_" is a good description for a lathe that weighs about 250 pounds on its base cabinet.

The manual doesn't address a GFCI but specifically calls for a grounded outlet, which I have.  

Today, 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 GFCI, so that indicates the ground is the issue. I have an oscilloscope and could see lots of high frequency noise on the AC line. At the moment, I'm not comfortable enough with that measurement to put a number on it.

I'd rather keep the GFCI for my milling machine because I use water-based coolant on it.  I'm still studying.


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## salindroth (Jan 8, 2020)

MontanaAardvark said:


> 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.
> 
> ...


Coming late to this thread, but I had the same problem with my LMS lathe and mill.  I wrote to LMS and Chris Woods replied that I should not use GFI outlets because "these machines turn your AC into DC, then reassemble it to 3-phase. The phase shift unbalances the hot and neutral." 

Scott


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## middle.road (Jan 8, 2020)

Another 2cents which may not even apply to this,
Lived in a sub-division several years ago that was built by a crooked contractor.
All the houses were less than 10 years old at that time.
We kept experiencing weird trips on both conventional and GFCI circuits. Blew out a few computers before I scored some extra UPSes.
To make a long story short the electrical utility came through and pulled all the meters and re-did the lugs and replaced the meters.
One of the neighbors had a small fire inside their meter box and that was what triggered the repairs.
I talked to the supervisor when they were affecting the repairs and he said that all 24+ homes had not been installed properly.


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## MontanaAardvark (Jan 8, 2020)

salindroth said:


> Coming late to this thread, but I had the same problem with my LMS lathe and mill.  I wrote to LMS and Chris Woods replied that I should not use GFI outlets because "these machines turn your AC into DC, then reassemble it to 3-phase. The phase shift unbalances the hot and neutral."
> 
> Scott


I've come to the conclusion that was the cause of the problem with my lathe.  That and if you look on the Chris' Tips tab for their page on this lathe, it says something like, "we don't expect any of our machines to run on a GFCI"  Then they quote a justification from the national electrical code saying the GFI outlet isn't required in a case like this: a big, non-portable machine plugged into the wall.  An electrician tells me that has been removed from the code in the 2014 update.

Anyway, I've just moved the plug for the lathe into an outlet that doesn't have a GFCI, just a good ground, which is what the manual calls for.


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