Brand New PowerMatic 3520C powers on, but trips breaker when RPM turned up

[jrista]

I purchased a PowerMatic 3520C about a month or so ago (maybe closer to two now). Just turned it on today...and it seems to trip the breaker when I turn up the RPM above 0. It powers on fine, the RPM meter lights up, the green on light lights up when I press the green button, and it'll be fine until I turn up the RPM...

It was on sale when I bought it, $4800 plus extras valued at a couple hundred more. List price on these things now is around $5700, and I just couldn't pass up the opportunity. Well, it shipped and arrived a heck of a lot faster than I expected, and was delivered before I had a chance to install 240V power for it. I had a few electricians come by, and the price just to install a GFCI two-pole 20A breaker, some romex and an outlet was anywhere from $1600 to a whopping $2156. After pricing out the parts myself (a few hundred bucks...romex is expensive nowadays, $108 just for some 12/2, $218 for 12/3, the GFCI breaker was $104, plus a few other parts), realized these guys were trying to take me for a ride with the labor charges.

I ended up wiring in the new breaker, romex and a twist-lock 240V outlet myself (along with a few other things, like a light switch for my new overhead shop lights, a switch and some new GFCI outlets for my drill press and bandsaw, etc.) I triple tested everything with my multimeter, and its all good. I get 123.8v from ground to either black and white (normally red, but I used 12/2 to save some money), and 248V between black and white. This is true at every point along the path from the breaker to the outlet, at the three wires at the other end of the power cable that came with the lathe (which I wired into a 240V twist-lock plug), as well as from the 1 (black) and 3 (white) terminals inside the main switch box in the PowerMatic itself. The power is rock solid stable, it fluctuates maybe ~0.1V occasionally, but otherwise its super stable. So, I believe everything is wired up properly...I don't think there are any ground faults within the wiring job itself from the breaker to the end of the power cable anyway.

With all of that new wiring installed and tested, today I finally had some people come by to help me set up the lathe. It was heavier than I expected...online I thought I saw that the weight was 430lb, turned out to be 726lb in total...so it took three of us to set everything up, and maneuver the bed and stand around, and finally get the headstock on. Finally connected the power cable to the on/off master switch on the back of the lathe, and powered it up for the first time (yes, sadly, probably close to two months after I bought it!! ) After a moment the lights came on, and I thought I was in business...until I turned up the RPM. I am curious why the lathe would power on fine, and show the control panel lights and all that...and only trip the moment I try to turn up the RPM? I am going to be calling PowerMatic on monday of course, but I'm curious if anyone can think of a reason why this might be happening? Its tripping the GFCI breaker...I suspect its a ground fault, as the red indicator on the breaker appears...but, the fault only seems to occur when the motor finally starts to rotate. This lathe seems to have a VFD to control the motor, probably because it is a 3-phase motor. The VFD has a little plastic cover on the back, and if I pull that out I can see a port of some kind...which makes me wonder if it can be tweaked or tuned to account for differences in voltage?

The manual says the motor requires 230V 1-phase power, and my power is single-phase, but its nearly 250V... Is it possible that the extra 20V of voltage is causing a problem? Or is there more likely a problem with the motor itself? OR something with the VFD?

Thanks...

 

[woodcutter199]

I purchased a PowerMatic 3520C about a month or so ago (maybe closer to two now). Just turned it on today...and it seems to trip the breaker when I turn up the RPM above 0. It powers on fine, the RPM meter lights up, the green on light lights up when I press the green button, and it'll be fine until I turn up the RPM...

It was on sale when I bought it, $4800 plus extras valued at a couple hundred more. List price on these things now is around $5700, and I just couldn't pass up the opportunity. Well, it shipped and arrived a heck of a lot faster than I expected, and was delivered before I had a chance to install 240V power for it. I had a few electricians come by, and the price just to install a GFCI two-pole 20A breaker, some romex and an outlet was anywhere from $1600 to a whopping $2156. After pricing out the parts myself (a few hundred bucks...romex is expensive nowadays, $108 just for some 12/2, $218 for 12/3, the GFCI breaker was $104, plus a few other parts), realized these guys were trying to take me for a ride with the labor charges.

I ended up wiring in the new breaker, romex and a twist-lock 240V outlet myself (along with a few other things, like a light switch for my new overhead shop lights, a switch and some new GFCI outlets for my drill press and bandsaw, etc.) I triple tested everything with my multimeter, and its all good. I get 123.8v from ground to either black and white (normally red, but I used 12/2 to save some money), and 248V between black and white. This is true at every point along the path from the breaker to the outlet, at the three wires at the other end of the power cable that came with the lathe (which I wired into a 240V twist-lock plug), as well as from the 1 (black) and 3 (white) terminals inside the main switch box in the PowerMatic itself. The power is rock solid stable, it fluctuates maybe ~0.1V occasionally, but otherwise its super stable. So, I believe everything is wired up properly...I don't think there are any ground faults within the wiring job itself from the breaker to the end of the power cable anyway.

With all of that new wiring installed and tested, today I finally had some people come by to help me set up the lathe. It was heavier than I expected...online I thought I saw that the weight was 430lb, turned out to be 726lb in total...so it took three of us to set everything up, and maneuver the bed and stand around, and finally get the headstock on. Finally connected the power cable to the on/off master switch on the back of the lathe, and powered it up for the first time (yes, sadly, probably close to two months after I bought it!! ) After a moment the lights came on, and I thought I was in business...until I turned up the RPM. I am curious why the lathe would power on fine, and show the control panel lights and all that...and only trip the moment I try to turn up the RPM? I am going to be calling PowerMatic on monday of course, but I'm curious if anyone can think of a reason why this might be happening? Its tripping the GFCI breaker...I suspect its a ground fault, as the red indicator on the breaker appears...but, the fault only seems to occur when the motor finally starts to rotate. This lathe seems to have a VFD to control the motor, probably because it is a 3-phase motor. The VFD has a little plastic cover on the back, and if I pull that out I can see a port of some kind...which makes me wonder if it can be tweaked or tuned to account for differences in voltage?

The manual says the motor requires 230V 1-phase power, and my power is single-phase, but its nearly 250V... Is it possible that the extra 20V of voltage is causing a problem? Or is there more likely a problem with the motor itself? OR something with the VFD?

Thanks...

check the amperage. If it is more than 25 or 30 amps then the wire is too small to start up how ever I think if you took the GFCI breaker out of the loop the problem will solve itself

 

[jrista]

check the amperage. If it is more than 25 or 30 amps then the wire is too small to start up how ever I think if you took the GFCI breaker out of the loop the problem will solve itself

By law in Colorado, I have to have the GFCI breaker for any device out in a garage, which is where my lathe is...

I'm curious, though...why would you just take the GFCI out of the loop? Wouldn't that pose potential risks?

EDIT: Oh, and the breaker is a 20A breaker, but the lathe's draw is like 6.5 amps on average, with I think a max of 9.

 

[rixstix]

Dadgum tablet keyboard

 

[rixstix]

Oops

 

[egnald]

Hmmm - Are you sure you have the right GFCI breaker and have it installed properly?

The breaker should pick up L1 and L2 from the bus in the panel and should have a pigtail (coiled wire) coming out of it (usually a white wire). This pigtail wire must be connected to a Neutral block inside the panel for the GFCI breaker to work properly.

If your lathe requires a Neutral to power any 120V circuits or accessories, you need to have a GFCI Breaker that has a "Load Neutral" lug connection in addition to the L1 and L2 lugs. This is where the Neutral to the Load gets connected. In other words, if the Load needs a Neutral, the Neutral needs to go through the breaker and can not be connected directly to a Neutral bar in the panel.

Regards,
Dave

PS I will make a sketch that shows wiring of a GFCI breaker to both a 4-wire Device and to a 3-wire device and will post it shortly.

 

[jrista]

Hmmm - Are you sure you have the right GFCI breaker and have it installed properly?

The breaker should pick up L1 and L2 from the bus in the panel and should have a pigtail (coiled wire) coming out of it (usually a white wire). This pigtail wire must be connected to a Neutral block inside the panel for the GFCI breaker to work properly.

If your lathe requires a Neutral to power any 120V circuits or accessories, you need to have a GFCI Breaker that has a "Load Neutral" lug connection in addition to the L1 and L2 lugs. This is where the Neutral to the Load gets connected. In other words, if the Load needs a Neutral, the Neutral needs to go through the breaker and can not be connected directly to a Neutral bar in the panel.

Regards,
Dave

I am pretty sure it is the right GFCI breaker. Has the pigtail neutral, that's connected to the neutral bar in the box.. Has three terminals, but with the 12/2 romex I just connected black to one of the hots, and white to the other, there is currently no neutral wire going from the breaker to the wall receptacle. The ground is of course connected to the ground bar in the box. Its a BIG breaker...2x 1" wide, with the red test button and a test indicator light. I tested the GFCI before I connected the cable plug to the receptacle, and it tripped properly.

The lathe has a three-wire cable that came with it, and its a 240V machine: 1 black, 1 white, 1 green/ground. The instructions say nothing about a neutral. They don't even talk about wire colors, it just says connect the two hots to the two terminals on the switch inside the box on the back of the headstock...that box already had a three-wire going from it, to the control box, and that cable was black, white and green/ground. So white, in this case, is just another 120V hot, which is why I connected the 12/2 romex white to the other hot of the GFCI breaker. If the lathe had actually required a true neutral, then I suspect it would have had four wires internally (black and red hot, white neutral, and green/ground), right?

 

[jrista]

Here is the breaker box with everything wired in...the GFCI should be obvious:

I added a couple more outlets for some of my other machines, GFCI outlets instead of GFCI breakers as my subpanel is a GE that supports these half-size breakers as well as full-size breakers, and the GFCI breakers are always double-size full-size (so, ~2" wide, vs. the 1/2" wide that the normal breakers are...I simply wouldn't have been able to fit all the necessary GFCI breakers without replacing the entire panel.)

The twist-lock outlet is here (its been installed now):

 

[egnald]

I am pretty sure it is the right GFCI breaker. Has the pigtail neutral, that's connected to the neutral bar in the box.. Has three terminals, but with the 12/2 romex I just connected black to one of the hots, and white to the other, there is currently no neutral wire going from the breaker to the wall receptacle. The ground is of course connected to the ground bar in the box. Its a BIG breaker...2x 1" wide, with the red test button and a test indicator light. I tested the GFCI before I connected the cable plug to the receptacle, and it tripped properly.

The lathe has a three-wire cable that came with it, and its a 240V machine: 1 black, 1 white, 1 green/ground. The instructions say nothing about a neutral. They don't even talk about wire colors, it just says connect the two hots to the two terminals on the switch inside the box on the back of the headstock...that box already had a three-wire going from it, to the control box, and that cable was black, white and green/ground. So white, in this case, is just another 120V hot, which is why I connected the 12/2 romex white to the other hot of the GFCI breaker. If the lathe had actually required a true neutral, then I suspect it would have had four wires internally (black and red hot, white neutral, and green/ground), right?

Yes - that is correct. It sounds like a 3-wire device (L1, L2, Ground). I just didn't know if there were any 120V accessories on your lathe - a 120v light for example. - Dave

 

[egnald]

Here is the breaker box with everything wired in...the GFCI should be obvious:

View attachment 332096


View attachment 332098

I added a couple more outlets for some of my other machines, GFCI outlets instead of GFCI breakers as my subpanel is a GE that supports these half-size breakers as well as full-size breakers, and the GFCI breakers are always double-size full-size (so, ~2" wide, vs. the 1/2" wide that the normal breakers are...I simply wouldn't have been able to fit all the necessary GFCI breakers without replacing the entire panel.)

The twist-lock outlet is here (its been installed now):

View attachment 332099

According to your pictures, it sure looks like everything is wired correctly. I am assuming this is a sub-panel thus the 4 heavy Gauge wires coming into the panel from the bottom. The only thing I can think of checking is that the heavy Neutral is tied to the heavy Braid back at the main panel, but it would surprise me if it isn't.

You certainly have a puzzle on your hands. Obviously there is some kind of current imbalance between L1 and L2 (or some kind of over-current short) that is causing the breaker to trip.

I'm afraid I've exhausted everything I can think of that could be causing this.

Dave

 

[jttheclockman]

First let me say that VFD motors do not play well with GFCI breakers or outlets. Harmonics will cause stray currents on opposing wires and create stray voltages. A couple things because I did not read all you wrote. How long is your run to this sub panel from main and then from the sub to the lathe. Undersized wires will have an effect. How is your ground connected. . Next that white neutral should not be grounded to the panel Do not use the bonding screw on the neutral.. Not knowing how you wired things and you said you installed everything. Those are the first things to look for.

The next thing is how old is this lathe?? They have made improvements on VFD lathe by adding filters. You may want to call dealer and find out if you can hook this lathe on a GFCI.

You do not say what type(brand) breaker is used. They do sell hospital grade breakers as well as GFCI outlets that are better grade. Too many unknowns here to be able to answer why.

From what I see that is an isolated neutral bar and it is not bonded to the panel which is good.

One thing about questioning the price, if you included all the other work those prices could be right in line depending on where you live.

 

[jrista]

First let me say that VFD motors do not play well with GFCI breakers or outlets. Harmonics will cause stray currents on opposing wires and create stray voltages. A couple things because I did not read all you wrote. How long is your run to this sub panel from main and then from the sub to the lathe. Undersized wires will have an effect. How is your ground connected. The ground wire in the sub panel should not be grounded to the box. It should be continuous back to the main panel. You should not have a screw that goes through the ground bar in the sub panel that connect to panel It should be a floating ground bar. Next that white neutral should not be grounded to the panel either. Not knowing how you wired things and you said you installed everything. Those are the first things to look for.

The next thing is how old is this lathe?? They have made improvements on VFD lathe by adding filters. You may want to call dealer and find out if you can hook this lathe on a GFCI.

You do not say what type(brand) breaker is used. They do sell hospital grade breakers as well as GFCI outlets that are better grade. Too many unknowns here to be able to answer why.

So, I had the subpanel professionally installed about a year and a half ago. An electrician brought the fat gray cable over from a 100A breaker on my main panel, and as far as I can tell all of that is wired up properly. The ground from the subpanel goes back to the ground on the main panel, as does the neutral. The run is diagonal across the size of my house...sadly, the main box is at the opposite corner of my house from where this subpanel was. The electrician I had install it spent a good deal of time figuring out how to route it, and the cable he used is over about an inch and a half thick (and the black, red, white and ground wires in it are around 3/8" thick, maybe more). He actually managed to route it pretty much direct, so its the shortest distance possible between the subpanel and the main panel.

Regarding floating ground and neutral bars...I'll have to get in and take a closer look at those...I am not sure.

The lathe is literally brand new. It was manufactured last year, I bought it either the very end of january, or the very beginning of february.

I thought I had mentioned the breakers were GE...but I'm not finding it now. Anyway, the subpanel, breakers, are all GE. Most of the breakers are the half-height ones, which I think are only available from GE. The GFCI breaker was actually $124. It was the only one I could find, they have been out of stock everywhere that I've looked... Ironically now, it is starting to sound like I didn't even need it?

So, from what you have said, which backs up what @woodcutter199 said, it is sounding like the GFCI breaker itself may in fact be a problem with this lathe?

 

[jttheclockman]

I looked again at your photos and a few I was able to blow up. It looks like the ground bar is fine and it looks like the neutral bar is floating and not bonded. If an electrician did it then it should be fine because he knows not to bond a sub panel.

As far as not needing it is different than being able to use it. Code dictates what is needed in each state and area of the state. Now if you eliminate it and things work well than that is a homeowners choice. Just telling you VFD are notorious for not playing well with GFCIs as is electronic ballasts. Old refrigerators do not play well with GFCI outlets. Anything with a compressor can be a problem.

I won't even ask about the outlets you ran and what you put them on? Electricity is nothing to take lightly. Yes it may work but was it wired correctly?? That is why Electricians get $$$

 

[jrista]

I looked again at your photos and a few I was able to blow up. It looks like the ground bar is fine and it looks like the neutral bar is floating and not bonded. If an electrician did it then it should be fine because he knows not to bond a sub panel.

As far as not needing it is different than being able to use it. Code dictates what is needed in each state and area of the state. Now if you eliminate it and things work well than that is a homeowners choice. Just telling you VFD are notorious for not playing well with GFCIs as is electronic ballasts. Old refrigerators do not play well with GFCI outlets. Anything with a compressor can be a problem.

I won't even ask about the outlets you ran and what you put them on? Electricity is nothing to take lightly. Yes it may work but was it wired correctly?? That is why Electricians get $$$

Everything is wired correctly. I've done enough with electrical wiring in my time. I had a pro install the panel, because its a much bigger job, and the guy had a reasonable price, and did it in a matter of a few hours.

The outlet is a 20A 240V twist-lock receptacle with the corresponding plug. The romex is 12/2 (the yellow cabling in my photos), which is plenty for the ~6.5A average, 9A peak draw from the lathe. I thoroughly tested everything for continuity and voltage throughout the process.

Electricians aren't worth >$1000 (only labor!!) for a breaker, romex run and receptacle install....sorry, not a chance. I could understand a few hundred bucks to do that, a pro shouldn't need much more than an hour to do something that simple....but these guys are of their rocker for what they are asking for a basic install. The labor cost these guys are asking for around here is incomprehensibly insane.

 

[jttheclockman]

Come on now. I think you have been around long enough to know the game. It is not only electricians but it could be any trade. They maybe so busy they really did not need your job but threw a high number out and if you took it they were ahead. You see this all the time. Roofers, siding guys landscapers. It happens in every state.

I am glad you feel competent enough to do your own electrical work. Good luck with your lathe.

 

[jrista]

https://acim.nidec.com/drives/kbelectronics/-/media/kbelectronics/documents/white-papers/updated-using-vfds-on-gfci-devices.ashx?la=en

Well, this was informative, Sounds like the issue is likely the combination of vfd and gfci.

 

[rherrell]

I had the same problem with my Jet 1642 with a VFD, I replaced the gfci with a standard receptacle and that solved the problem.

 

[rixstix]

Another example of the need to remove the GFCI, the LMS 7350 manual specifically states that it will NOT function correctly if plugged into a GFCI protected receptacle, thus my need to rewire part of the basement next week.

Does the manual state the lathe to be hardwired or state that a plug/cord is acceptable?

LMS 7350 Electrical Safety
• Plug the machine into a grounded receptacle. Note that the machine does
not work properly on a ground fault circuit interrupter (GFCI) receptacle...

 

[MRDucks2]

Check and see if your gfci breaker has a lug for a neutral wire. This will typically be right around the white pigtail wire itself.

Think about the type of gfci breaker you are using. The white wire is tied to the neutral bus typically to compare neutral to something else (probably ground). You have no neutral wire (you are right, not needed on a VFD application). Any time you go to power up the gfci breaker has nothing on the load side to reference so presumes there is some kind of fault.

If there is no connection for a neutral on the breaker this thought will not apply.

 

[monophoto]

By law in Colorado, I have to have the GFCI breaker for any device out in a garage, which is where my lathe is...

I'm curious, though...why would you just take the GFCI out of the loop? Wouldn't that pose potential risks?

EDIT: Oh, and the breaker is a 20A breaker, but the lathe's draw is like 6.5 amps on average, with I think a max of 9.

I suspect that this is a problem of interaction between the variable speed drive in the lathe and the GFCI. GFCI's use electronic gadgetry to detect when current that flows out of the 'hot' terminal of a receptacle flows back to the source on any path other than the normal neutral, and are extremely sensitive so that they can detect anomalous current flows that are below the threshold that causes heart fibriliation. As I recall, the sensitivy is somewhere around 0.005 amperes - which is microscopic compared with the normal current flow into the lathe. There are a number of things that can cause small false error currents and fool GFCI's into tripping erroneously. My suspicion is that the power converter in the lathe is generating harmonic currents that flow back into the grid and that can confuse the GFCI into thinking that there is an abnormal current flow.

I am a retired electrical engineer, and prior to retirement, I occasionally had a need to deal with National Electrical Code issues, but I never considered myself to be a NEC authority - the NEC is a complicated document that is revised periodically, and following the code is a real specialty. I suspect Colorado law is based on the National Electrical Code which requires that there be a GFCI on convenience receptacles in a garage, kitchen, bathroom, or anywhere outdoors. The electrical code defines how electricians are supposed to do installations to protect people, but the code can't do anything about the situation when a civilian does something stupid with a non-permanent device temporarily plugged into a receptacle. That's where GFCI's come in - they are intended to protect people from electric shock.

A professional electrician is not going to do something that he knows will not be approved by the inspector. But the fact that you did your own installation means that it may never be inspected although doesn't give you the freedom to ignore NEC requirements.

Ultimately, the local electrical inspector is the final authority to interpret the requirements of the NEC for any permanent installation. I don't think that the NEC requires GFCI's on circuits that are hard-wired (no receptacles) to furnaces, water heaters or sump pumps on the basis that it can be presumed that they are manufactured and tested to meet UL requirements and therefore the design addresses all electrical shock hazards. (Hard-wired pool pumps are an exception to this rule because of the more immediate hazard to persons.)

It might be possible to convince an electrical inspector that the twist-lock receptacle you chose to use on your lathe effectively makes the lathe a permanently-installed device, and therefore a GFCI isn't required, especially if the only device in your shop that can connect to that receptacle is the lathe that is equipped with a plug that mates with that receptacle . However, general purpose electrical receptacles in your shop, regardless of voltage, would need to be protected by GFCI's because the electrician and inspector have no control over what gets plugged into those receptacles.

However, if that argument isn't convincing, then taking the next step and removing the receptacle altogether - hard-wiring the lathe to the power source - should eliminate the need for having a GFCI on the lathe circuit (subject to agreement by the inspector). However, that would also raise a new concern that there should be some means of disconnecting the lathe from the power source in event it needs service. I think a lockable wall-mounted switch would satisfy that requirement.

 

[egnald]

From everyone's input it sounds like your sub-panel was installed correctly with the appropriate bonding scheme between the Neutral and Ground. The information related to VFD harmonics causing nuisance tripping on GFCI and the fact that your lathe powers on and only trips the breaker when you start running the motor (via the VFD controller) also points to the VFD - GFCI interaction.

Licensed Electricians and Electrical Inspectors are required to follow the electrical code to keep their respective licenses and liability insurance. In general the codes are in place to guarantee the safety of the end user, so they are going to follow the code to the letter.

Colorado statutes related to Electrical Inspection include a provision to request a Code Variance for specific installations. It is done submitting a Colorado Variance Request Form to the Colorado State Electrical Board for their approval. I think your situation would be a prime candidate for such an approval to replace the GFCI breaker with a traditional breaker, especially if you eliminate the 240 V receptacle and wire your lathe to an appropriate Lock/Out capable Electrical Disconnect Switch.

Regards,
Dave

 

[jrista]

Thanks, everyone, for the input. I'm pretty sure the issue is VFD-GFCI incompatibility. I'm going to pick up a standard 20A 240V breaker and pop that in and see if it solves the problem.

As for code compliance... @monophoto Thanks for all the detail, I appreciate it. Colorado adopted the 2020 NEC around August 2020 IIRC. It does look like the NEC only requires the GFCI when a receptacle is involved...I didn't realize that. I wonder why...is it potentially because a human could touch the leads with a plug and cause a short themselves?

I know that the GFCI breaker I have should trip when there is a variation in current between the two hots (or the hots and a neutral, if a neutral is used...not used in my case) of just 4-6mA. Given that, I understand now why the VFD is causing it to trip...6-4mA is just noise for a motor load. It sounds like there are some 30mA GFCI breakers that might help, but its not guaranteed that it would completely eliminate nuisance tripping.

I am not entirely sure how I would permanently wire this. The power cable that came with the lathe is stranded wire, whereas the romex is of course solid core copper. Not sure of any reliable way to permanently wire those two together other than to solder the stranded to the solid core. I am not sure a normal wirenut is going to do the job...I'd worry it would slice the strands of the stranded.

 

[jttheclockman]

Check and see if your gfci breaker has a lug for a neutral wire. This will typically be right around the white pigtail wire itself.

Think about the type of gfci breaker you are using. The white wire is tied to the neutral bus typically to compare neutral to something else (probably ground). You have no neutral wire (you are right, not needed on a VFD application). Any time you go to power up the gfci breaker has nothing on the load side to reference so presumes there is some kind of fault.

If there is no connection for a neutral on the breaker this thought will not apply.

Sorry but this is not true. A GFCI will also work with no neutral on a 220volt system when no neutral is required at load. It senses current flow between two hots and or ground. Proof is he powered lathe and did not trip breaker.

 

[jttheclockman]

Thanks, everyone, for the input. I'm pretty sure the issue is VFD-GFCI incompatibility. I'm going to pick up a standard 20A 240V breaker and pop that in and see if it solves the problem.

As for code compliance... @monophoto Thanks for all the detail, I appreciate it. Colorado adopted the 2020 NEC around August 2020 IIRC. It does look like the NEC only requires the GFCI when a receptacle is involved...I didn't realize that. I wonder why...is it potentially because a human could touch the leads with a plug and cause a short themselves?

I know that the GFCI breaker I have should trip when there is a variation in current between the two hots (or the hots and a neutral, if a neutral is used...not used in my case) of just 4-6mA. Given that, I understand now why the VFD is causing it to trip...6-4mA is just noise in for a motor load. It sounds like there are some 30mA GFCI breakers that might help, but its not guaranteed that it would completely eliminate nuisance tripping.

I am not entirely sure how I would permanently wire this. The power cable that came with the lathe is stranded wire, whereas the romex is of course solid core copper. Not sure of any reliable way to permanently wire those two together other than to solder the stranded to the solid core. I am not sure a normal wirenut is going to do the job...I'd worry it would slice the strands of the stranded.

There are statements in here that are not correct or are grey areas, but will not go into them because as I always said when people ask electrical questions on an open forum a couple things come into play. The ability of the person doing the work is not known. Explaining things in writing can lose the message and all steps may not be included. Each state has their own codes as well as the NEC which is basic standards. Not knowing them can lead to false info. Basic questions can turn into unsafe questions.

Now to the last part of the statement and splicing solid wire and stranded wire, it is done all the time( lighting fixtures as an example) and care just be followed especially not having strands outside a wirenut or connector. But must be installed in a junction box mounted to a solid surface and not floating on the floor. But with that said, if I were you I would get a nonfused disconnect and connect the line and load into it to give you power disconnect capabilities to be able to work on tool if need be. When doing this code states it must be lockout capable and they basically all are with holes in the latch for either a lock or tag. Again following codes. This applies to tablesaws and other machinery. Now your panel is in the garage so you can get away with the use of disconnect because you can use the breaker and the ability to lock out the panel

 

[MRDucks2]

Sorry but this is not true. A GFCI will also work with no neutral on a 220volt system when no neutral is required at load. It senses current flow between two hots and or ground. Proof is he powered lathe and did not trip breaker.

There are GFCI devices that reference a balance between neutral and ground, also. In that application, would the missing neutral at the source result in an imbalance?

 

[jrista]

There are GFCI devices that reference a balance between neutral and ground, also. In that application, would the missing neutral at the source result in an imbalance?

For 240V, the two opposing (or phase shifted) 120V signals effectively "find their own neutral" so a neutral wire is not always necessary. With 240V devices that may power other lower-powered 120V loads in addition to a high powered load, you may need a neutral to support the wiring of those additional loads, since they would operate off of normal 120V power, and thus would need a return path (neutral.)

This machine is just strait up, simple 240V power, so it has a ground, and two hots. There is nowhere to connect a neutral line anyway, so I didn't bother to connect one to the GFCI. This GFCI breaker can detect faults either by differential between the two hots, or the differential between either hot and the neutral, so it is not required to include the neutral. The breaker itself connects to the neutral bar, so it has its own neutral reference.

There are also 120V GFCI breakers, which have two lead terminals, one for hot and one for neutral. The neutral would be required in that situation, since 120V loads need that return path.

 

[jrista]

For those who offered their insights. I popped in a standard 20A 240V breaker, connected the two lines to the two terminals, and the lathe runs just fine. So it seems the issue was VFD nuisance tripping of the GFCI. I'll circle back around and re-wire the lathe so its hardwired down the road once I have a chance to figure out how best to do that, for now...I've been out of the game for about two months now, and have a pile of things that need to be turned.

 

[egnald]

For those who offered their insights. I popped in a standard 20A 240V breaker, connected the two lines to the two terminals, and the lathe runs just fine. So it seems the issue was VFD nuisance tripping of the GFCI. I'll circle back around and re-wire the lathe so its hardwired down the road once I have a chance to figure out how best to do that, for now...I've been out of the game for about two months now, and have a pile of things that need to be turned.

Woo Hoo! Congratulations. I'm glad you are finally back in business! - Dave

 

[jttheclockman]

There are GFCI devices that reference a balance between neutral and ground, also. In that application, would the missing neutral at the source result in an imbalance?

No unless you are talking 120V outlets. He has a 220V GFCI that has the neutral terminal on the breaker and if there was a load source neutral then it would monitor that as well. In his case he is not using the terminal so it only monitors the 2 hots. If he needed a 3wire source to load then he would have to include the neutral for lights or sometimes they have an outlet on a tool. Then it would monitor the neutral but he would have needed to run a 3 wire with 2 hots and a neutral. Wire in cable form the ground is not counted as a wire because it is always there. Thus 12/2 or 12/3 or 12/4 but each cable would have also a ground.

 

[Charlie_W]

Glad you have your C up and running….Sweet lathe!
The issue of electronic variable speed lathes tripping GFCIs is not a new issue and has been discussed here over the years.
Since everyone has taken care of the tech/electrical discussion, I'll just add that a friend has a turning studio with 9 full size lathes with 7 of them being 3520 B & C. Models.
All operate with absolutely no issues on non-GFCI breakers. He has one older Jet 1642, 110V that has to be plugged into a non protected receptacle (ceiling dust filter receptacle) as all the wall receptacles are protected.

Also a pain is when you are to demonstrate turning at a local craft fair and the provided receptacle is a GFCI. After too many trips to the outside receptacle to reset the GFCI, we learned to set the speed on the lathe before turning it on. These were some older Delta midi lathes.