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My lathe motor and GFI do not play nicely together.

R

Rick Bucker

Joined
Dec 26, 2020
Messages
51
Likes
5
Location
Leland, NC
My previous lathe played nicely with the GFI (ground fault interrupter). The GFI is in a 20 amp outlet.

My new lathe popped the GFI on each of the three circuits in the shop. It ran nicely when I used a very long extension cord and plugged it into a non-GFI protected circuit in the house. Several friends with the same lathe did not have a problem with it tripping the GFI.

The outlet GFI's were made by Leviton. I called them to see if they had any suggestions and was forwarded to a GFI specialist. After getting a nice brief discussion on how a GFI works, he asked more about my problem. I told him about my new lathe popping every GFI circuit that I tried to use. He said that some motors will do that. Several people previously gave me suggestions such as getting a different lathe, upgrading the GFI to a hospital grade GFI, and using a GFI breaker. He told me that the electronics in each grade of GFI are the same. There are differnces in the construction of the GFI. He said that a GFI breaker would not work. He said that in 2015 the specifications for a GFI became stricter and homes built starting in 2016 would have the new GFI recepticals. He thought that my lathe may not trip one made prior to the change. He then said that another option that would meet the electrical code would be to plug it into a dedicated non-GMI circuit in the shop. The motor/electronics on my lathe could not be converted to 220. But I had an unused 220 circuit and had an electrician change it from a 220 circuit to a single outlet 110 non-GFI circuit that works with my lathe.

I just wanted to let others know how the problem was addessed in case you encounter a similar issue with a new lathe in the future.

Rick
 
Gerald Lawrence said:
I have to wonder why anyone would want GFI in the shop, unless it is in the home. But that is just me. I do not have any in mine but is a detached building.
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The shop is attached to a two car garage (a third bay) and has a door to the garage. The builder and the electrical inspector said that GFIs were required to meet the electrical code.
 
I don't have a restroom or any water in that room. It was explained to me that garages require GFI and this room is basically an extension of the two car garage that has been insulated and has a wall with a door between it and the two car garage. The builder said it required GFIs and his electrician said the same thing. With the dedicated circuit for the lathe, everything is now working fine.
 
If you have a variable speed lathe with a VFD controller, the VFD will feed a lot of RF back into the power line. Did Leviton mention anything about putting an RF filter on the power line? I had a lot of problems with electronic gear in the shop until I added an RF filter between the lathe and power outlet.
 
Dave Mueller said:
If you have a variable speed lathe with a VFD controller, the VFD will feed a lot of RF back into the power line. Did Leviton mention anything about putting an RF filter on the power line? I had a lot of problems with electronic gear in the shop until I added an RF filter between the lathe and power outlet.
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I asked about filters and he said that they would not work. He explained that the GFI measures the outgoing current on the red wire and measures the incoming current on the neutral wire. If the difference exceeds a certain milliamp value, the GFI then trips. He aid that inductive motors do not play nicely with GFIs for this reason.
 
It is my understanding that, according to current code, any room with a concrete floor must have GFI. Which means that a workshop in most garages or basements should have GFI outlets. Some lathe menufacturers state that their lathes don't work with GFI, but none seem to offer a solution. Are there any electricians in AAW land who know how to fix this?
 
We're quite explicit about our VFDs not working on 110v GFI circuits. The solutions seem to be wiring a dedicated non-GFI 110v circuit as mentioned above; running a 220 circuit and converting your unit to that voltage (most 110v VFD's can be rewired 220 quite simply - I know ours can) or running a heavy extension cord somewhere to a non-GFI 110v circuit. Often, the plug in for a garage door opener is in the ceiling, and non-GFI as it is difficult to make human contact between that unit and the floor.
 
Rick Bucker said:
I don't have a restroom or any water in that room. It was explained to me that garages require GFI and this room is basically an extension of the two car garage that has been insulated and has a wall with a door between it and the two car garage. The builder said it required GFIs and his electrician said the same thing. With the dedicated circuit for the lathe, everything is now working fine.
Click to expand...
I think that GFIs are a code requirement in spaces with concrete floors, but I certainly don't have expert knowledge of codes.
 
Is GFI incompatibility a problem for other machinery motors (e.g. band saw; circular saw)?

Is it just VFD's? Anyone with experience with DVR motors and GFI?
 
My Powermatic 2014 doesn't play nice with GFCI. My workaround was to replace the single-gang box the GFCI receptacle was in with a double-gang box and install a non-GFCI receptacle in the box next to the GFCI. The breaker is wired to the non-GFCI receptacle, which in turn is wired to the GFCI. The lathe plugs into the non-GFCI, and other tools (grinder, vacuum pump) are on the GFCI.
 
As far as I know, AC induction motors aren't a problem, but the very essence of VFD operation which is switching high voltage high-current power to the motor at a PWM frequency of approximately 8 kHz makes it a problem for other nearby sensitive electronic devices.

Rick, hopefully, the VFD and motor on your lathe can be reconfigured for 240 volts AC dedicated branch circuit per Brent's suggestion. That is the ideal solution.
 
So maybe I'm missing a step, but what I'm hearing is that GFI incompatibility is not an issue at 240V, and at 120V it's only an issue for VFD's. So is there such a thing as a 120V VFD?
 
Mark Jundanian said:
So maybe I'm missing a step, but what I'm hearing is that GFI incompatibility is not an issue at 240V, and at 120V it's only an issue for VFD's. So is there such a thing as a 120V VFD?
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The GFI is only required for 120 volt circuits since a GFI is not readily available for 240 volt circuits
 
Mark Jundanian said:
So maybe I'm missing a step, but what I'm hearing is that GFI incompatibility is not an issue at 240V, and at 120V it's only an issue for VFD's. So is there such a thing as a 120V VFD?
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Yes. 110-120 volt VFD's are available for up to 1.5 HP. They are more expensive that 220-240 volt VFD's of the same horsepower, as the VFD must also buck up the voltage to 220-240 for the motor. We offer our 1.0 and 1.5HP machines in either 110/120 or 220/240. Some other lathe manufacturers do as well.
 
I had to solve this problem in another setting where I had no other choices and after many years, countless hours of research and consultation with engineers, and _many_ hundreds of dollars spent, the option I found that allowed me to reliably plug a 120V VFD into a GFI circuit was to interpose an AC/AC constant voltage isolation transformer between the VFD and GFI. These can be had for a couple hundred bucks heres an example of one for a small motor. That was on top of shielded cables and RF chokes, so I can't say it wasn't a combined effect.

In my shop, which doesn't get wet, I had GFI breakers on the inside receptacles only until the inspections were complete.
 
Brent@TurnRobust said:
We're quite explicit about our VFDs not working on 110v GFI circuits. The solutions seem to be wiring a dedicated non-GFI 110v circuit as mentioned above; running a 220 circuit and converting your unit to that voltage (most 110v VFD's can be rewired 220 quite simply - I know ours can) or running a heavy extension cord somewhere to a non-GFI 110v circuit. Often, the plug in for a garage door opener is in the ceiling, and non-GFI as it is difficult to make human contact between that unit and the floor.
Click to expand...
While checking out the problem with a Record Power Envoy Lathe, I found out that many lathe manufactureres do not suggest using a GFI circuit. Brett - thank you for your input.

Rick
 
When I built our house (about 20 years ago) I was told any outlet that you can stand on the ground/concrete had to be GFI protected. I have had issues with a number of them and usually just replace them with regular outlets.
 
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