Lathe power disconnect options

[William C Rogers]

I have the Laguna 18-36 lathe and the emergency stop switch is fixed in the headstock. I unplug the lathe every night and was thinking about putting some type of disconnect at the tailstock end to serve both to disconnect the power and use as an emergency stop at that end. What opinions do you have or what option are viable? Right now I would have to walk 25' to the breaker box to avoid crossing the line of fire.

i was even thinking of getting a 120/240 relay and one of the outdoor remote systems to do this.

[Prashun Patel]

LMK when you do it. I will copy ;)

[Roger Chandler]

I was told by a turner that VFD's do not like a power disruption using a switch to just shut the power down. An emergency situation, where a blank is coming lose or such is not a regular happening, but just to power down the lathe is perhaps too frequently. Here is his quote to me in an email...


You mentioned adding a shop-made pendant for remote on/off control. I'd be interested in knowing more about the design of the one your club members demonstrated at show and tell. I considered adding one to my G0766 a year or so ago, but decided it would take more effort than I wanted to put into it right now. It's my understanding that, with these sensitive VFDs, you have to add the switching circuit to the actual VFD circuitry at the headstock, not just put it between the 220v receptacle and the lathe's power cord. Switching the 220v power off and on to the inverter while the lathe is operating is supposedly not good for it.



Now for my part, I do not really know for sure, but I think this gentleman likely knows what he is talking about, so I am going to not put a power interruptor between the headstock and outlet because of this. Wired into the headstock circuitry might be the way to go, and not just a switch to kill the power for everyday use.

[George Troy Hurlburt]

To each his own, but I have 4 lathes on computers, I don't ever disconnect. I have seen sparks fly out of the plug-ins box. I have wood dust in the air and maybe even finish fumes. Having arthritis doesn't help any. It's been this way for almost twenty years. Once I plug a machine in that's it, unless I have to move it. Don't you think all the other plug-ins in your house is similar. Like computers, stove, washer, dryer, water heater, microwave, dishwasher, TV, stero,golf cart,etc.and electric furnace.

[David Delo]

LMK when you do it. I will copy ;)


I did PM you back on that other matter, did you get it?

[William C Rogers]

Hmm! So far what I have been doing is pushing the emergency stop and then unplugging the machine. I am somewhat remote and we see power disruptions about 4 times a year, so don't want a surge to fry my VFD. So I would push the emergency switch and then kill the power to the lathe. Is it wrong to use the emergency stop this frequently?

[John Keeton]

To each his own, but I have 4 lathes on computers, I don't ever disconnect... Don't you think all the other plug-ins in your house is similar. Like computers, stove, washer, dryer, water heater, microwave, dishwasher, TV, stero,golf cart,etc.and electric furnace.Aside from the electrical considerations, there is one other possible consideration. If you produce any revenue from your turnings, it is likely your lathe is not insured on your homeowners policy, whereas the household appliances are. My homeowners would not cover my shop building nor the contents without the commercial rider I have.

[Roger Chandler]

Hmm! So far what I have been doing is pushing the emergency stop and then unplugging the machine. I am somewhat remote and we see power disruptions about 4 times a year, so don't want a surge to fry my VFD. So I would push the emergency switch and then kill the power to the lathe. Is it wrong to use the emergency stop this frequently?The emergency stop is wired into the lathe circuitry, so the vfd accounts for it. If I understand correctly, it is just abruptly cutting power by means of wiring not run through the circuitry which has the vfd in the sequence. I have not investigated this personally, but am not willing to chance creating vfd problems, until somone like an electrical engineer [Sparky or Bill perhaps] can speak definitively to this.

It does seem to me, that a switch added to the power cord would be in sequence since the lathe cord is in sequence with the vfd wiring, though.......hummmm? Perhaps, it could be that the extra switch bypasses the emergency stop button that is in sequence with the vfd?

[William C Rogers]

The emergency stop is wired into the lathe circuitry, so the vfd accounts for it. If I understand correctly, it is just abruptly cutting power by means of wiring not run through the circuitry which has the vfd in the sequence. I have not investigated this personally, but am not willing to chance creating vfd problems, until somone like an electrical engineer [Sparky or Bill perhaps] can speak definitively to this.

It does seem to me, that a switch added to the power cord would be in sequence since the lathe cord is in sequence with the vfd wiring, though.......hummmm? Perhaps, it could be that the extra switch bypasses the emergency stop button that is in sequence with the vfd?

So now I'm totally confused! How should one power down the lathe and VFD. The emergency stop kills the power to the motor and display, but the VFD is still powered. Forgetting about the emergency stop, are we saying unplugging and replugging the lathe is a problem? Isn't that the same as putting a disconnect in line with the power?

what is recommended?

[Roger Chandler]

So now I'm totally confused! How should one power down the lathe and VFD. The emergency stop kills the power to the motor and display, but the VFD is still powered. Forgetting about the emergency stop, are we saying unplugging and replugging the lathe is a problem? Isn't that the same as putting a disconnect in line with the power?

what is recommended?I would not think so, because that is the way it is designed.....the stop button works in sequence with the vfd and other circuitry. If one has an extra switch, and shut off occurs by bypassing the circuitry, could that not allow for power surge, or simply gets the sequence off cycle? Again William, I am NOT AN EXPERT in electronics, but know enough that VFD's are sensitive equipment. That quote in blue from another turner gave me pause, as I was planning to put an extra shut off switch on my power cord by using an extension cord wired into a switch [appropriately sized wire of course]

I am wondering out loud, and you should seek more qualified advice than I can provide..........this quote came to my mind when I saw your question. I just know that until I could find out definitively from experts, that I would not do it personally and risk vfd damage. It may be that it won't damage the vfd, and I hope one of our creekers who is an electrical engineer can speak to this. You would be safe I think just uplugging the lathe.

[John Keeton]

The attached files are excerpts from the manual for the Revo 2436, which does have the remote switch. They are Greek to me, but perhaps one of you electrically gifted folks can find the answer from these.

[William C Rogers]

I would not think so, because that is the way it is designed.....the stop button works in sequence with the vfd and other circuitry. If one has an extra switch, and shut off occurs by bypassing the circuitry, could that not allow for power surge, or simply gets the sequence off cycle? Again William, I am NOT AN EXPERT in electronics, but know enough that VFD's are sensitive equipment. That quote in blue from another turner gave me pause, as I was planning to put an extra shut off switch on my power cord by using an extension cord wired into a switch [appropriately sized wire of course]

I am wondering out loud, and you should seek more qualified advice than I can provide..........this quote came to my mind when I saw your question. I just know that until I could find out definitively from experts, that I would not do it personally and risk vfd damage. It may be that it won't damage the vfd, and I hope one of our creekers who is an electrical engineer can speak to this. You would be safe I think just uplugging the lathe.

I understand what you are saying Roger. I just don't know about these things and hope someone can comment. I thinking two things. One is removing power via of a switch when the lathe is running (emergency) be pulling the plug and two removing power when the lathe is not running (pulling the plug). So maybe the emergency stop has circuitry to prevent damage to the VFD when the lathe is running. Like John I don't understand. I will call Laguna tomorrow to see what they say. I do remember they told me to unplug the lathe when not in use to prevent damage from power surges.

[John K Jordan]

I have the Laguna 18-36 lathe and the emergency stop switch is fixed in the headstock. I unplug the lathe every night and was thinking about putting some type of disconnect at the tailstock end to serve both to disconnect the power and use as an emergency stop at that end. What opinions do you have or what option are viable? Right now I would have to walk 25' to the breaker box to avoid crossing the line of fire.
i was even thinking of getting a 120/240 relay and one of the outdoor remote systems to do this.

I have an emergency stop switch on my PM3520b which is tied into the low voltage control circuit for the VFD, just like the main stop switch on the front of the lathe. This stops the lathe but doesn't kill the AC power. Killing the AC power results in delay when powered up again while the VFD boots up or something.

I do disconnect my lathes from the power when I leave the shop to minimize possible damage from power surges. (I had a VFD fail on a lathe that I kept plugged in all the time but I don't know if it was due to a power surge.) For the PM I use a double-pole switch mounted in a metal box stuck to the end of the end of the lathe with magnets. For another lathe, a Jet1642, I disconnect with a 110v power strip which also controls the lights over the lathe.

BTW, I do not like to disconnect things by unplugging or by turning off a breaker because receptacles and breakers are not designed for that. A relay would work nicely but would be complicated compared to a switch. To be complete, I read that a surge from lightning could come in on the ground wire too. However lightening can jump across the room so I'm not sure how you could perfectly protect from lightning without working under ground.

JKJ

[Glenn C Roberts]

Just put the tail stock shut off in series with the headstock shut off. Easy.

[Brice Rogers]

On the G0766, if you are running the lathe and hit the emergency switch, it will somewhat slowly coast to a stop. If I pull the AC plug, exactly the same will happen. If I rotate the speed control to zero it will slow down faster. The "reverse EMF (electro-motive force) apparently is dissipated in the output semiconductors. If I had installed the braking resistor, this power would have been dissipated in them.

Interestingly, the main power on switch has a latching relay in it. So, when it is off, there is no electrical voltage to anything other than the switch. When I press the main power-on switch, then it "latches" and applies power to the VFD, etc. So, when the main power is off, the lathe is somewhat isolated from the mains. BUT, if, say a 10,000 volt surge comes into the lathe, it may (or may not) jump past the main power-on/off switch. What do I do if there is an electrical storm coming in or I'm going out of town? I unplug the lathe. If I get hit by lightening, it is unlikely that the "jolt" will jump several feet. A quarter inch? Yeah, maybe.

[Leo Van Der Loo]

I have the Laguna 18-36 lathe and the emergency stop switch is fixed in the headstock. I unplug the lathe every night and was thinking about putting some type of disconnect at the tailstock end to serve both to disconnect the power and use as an emergency stop at that end. What opinions do you have or what option are viable? Right now I would have to walk 25' to the breaker box to avoid crossing the line of fire.

i was even thinking of getting a 120/240 relay and one of the outdoor remote systems to do this.

Bill I am not the VFD expert, however on the Canadian forum there are a few, and the use and addition of or changing of VFD to machines are discussed often enough.

So to show that these experts have no problem with shutting down and starting up of the VFD I’ll add this and if you want there is more on this and other threads on the forum.

You can see that this person has used the VFD for years and shut it down and start it up with no problem.

378590

Here is the first answer to the question of a spray gun activated trigger for the VFD to start and stop, there aare several more answers.

378591

[Keith Buxton]

Looking at the wiring diagram and pictures of the head stock on line you have 3 switches a 1 pot one switch is for fwd and rev another is main on/off switch and the last is emergency stop switch and the speed pot. when you are using the lathe and want to stop it to look at the turning you should use the speed control to stop it. when you are going to turn the unit off when you are done you should use the main on/off not the emergency and then unplug it. the emergency stop kills power to the motor an part of the vfd not all of it the emergency stop should be us for what it named for when something is going wrong and you need to stop quickly.

[William C Rogers]

I did talk to Laguna CS yesterday about power disconnect. They said it was no problem to unplug the lathe at the end of the day. I also asked them if in an emergency condition if the VFD would be damaged if the power was cut while the lathe is running and again said it would not damage the VFD. So right now I can use the breaker to kill power to the lathe in an emergergency situation without crossing the line of fire. However the breaker is about 15 feet from the lathe. Using a relay is beneficial if you are constantly turning on and off through the relay. I still plan to disconnect the power cord, so a relay is not beneficial. Eventually I will put a simple kill switch at the end of the lathe. It will be in the on mode and only used should there be a reason to kill the power in an emergency. Hopefully it will never see the off position except for initial testing. As far as wiring into the existing emergency stop, it is more than I want to try to figure out.

[Bert Delisle]

With most modern VFD controls the normal operation of start and stop are momentary push button switches, these switches usually are wired to programable "inputs" to the VFD to send pulse instruction to the vfd.
The E-Stop button is usually a "maintained" switch which means the signal is maintained off and must be manually pulled or twisted to turn it back on, usually wired to programable "input".
Depending on the VFD initial programming the "braking" function of the vfd under normal stop/start may be different than the E-stop "braking" function. E-stop likely will apply more braking action to stop the rotation quicker, based on the factory setting from the manufacturer of the lathe. Or it may simply just remove the run command and the work piece would just coast to stop.
In both cases the power to the computer /programable board and the DC buss is still applied. This means the computer portion, the cooling fan, and the DC portion of the inverter are still energized and ready to respond to operator action.
The cooling fan is important to keep running as the heat sinks used in the VFD can get very hot while running and need time to cool down, the fan is likely temperature controlled(mine is, I can hear it running, and it stops several minutes after a period of down time), lathe is still ready to run, just the internal VFD fan has stopped,
Switching off the main power switch or unplugging the cord will remove the incoming power totally resulting loss of cooling to these heat sinks and could result in damage to the electronic speed control components of the drive.
I suspect that the comments related to VFDs not liking "power off" switches in the main power line may be due to overheating of components because fan power was shut off.
Adding a remote stop start push button is a great convenience and safety feature, my magnetic remote switch box lets me place it where it is most convenient for me, out of the line of fire.

[William C Rogers]

With most modern VFD controls the normal operation of start and stop are momentary push button switches, these switches usually are wired to programable "inputs" to the VFD to send pulse instruction to the vfd.
The E-Stop button is usually a "maintained" switch which means the signal is maintained off and must be manually pulled or twisted to turn it back on, usually wired to programable "input".
Depending on the VFD initial programming the "braking" function of the vfd under normal stop/start may be different than the E-stop "braking" function. E-stop likely will apply more braking action to stop the rotation quicker, based on the factory setting from the manufacturer of the lathe. Or it may simply just remove the run command and the work piece would just coast to stop.
In both cases the power to the computer /programable board and the DC buss is still applied. This means the computer portion, the cooling fan, and the DC portion of the inverter are still energized and ready to respond to operator action.
The cooling fan is important to keep running as the heat sinks used in the VFD can get very hot while running and need time to cool down, the fan is likely temperature controlled(mine is, I can hear it running, and it stops several minutes after a period of down time), lathe is still ready to run, just the internal VFD fan has stopped,
Switching off the main power switch or unplugging the cord will remove the incoming power totally resulting loss of cooling to these heat sinks and could result in damage to the electronic speed control components of the drive.
I suspect that the comments related to VFDs not liking "power off" switches in the main power line may be due to overheating of components because fan power was shut off.
Adding a remote stop start push button is a great convenience and safety feature, my magnetic remote switch box lets me place it where it is most convenient for me, out of the line of fire.

Bert, thanks for the detail. I do have a better understanding regarding power relating to VFDs. Since I disconnect power when I am done for the day, it is important to leave the VFD power on for a few minutes for cooling rather than disconnecting immediately after shutting down. I understand that it is not good to disrupt power when the lathe is running. The emergency stop switch compensates for that by leaving power to the VFD and cooling fan. Although not ideal since that I don't have the capability to wire a remote emergency stop, would be to put a power disconnect at the end of the lathe. If used it would put the VFD at some risk due to cooling, but with power removed no additional heat would be generated. I would only use this option in an emergency situation and hopefully never.

[Glenn C Roberts]

William, Get a friend to wire the second emergency stop switch in series with the first. Now either switch will shut it down in the fashion Bert describes for emergency off mode. Easily accomplished.

[david privett]

it would have some disadvantages for sure if needed to be moved often. but most heavy equipment is hard wired and a manual throw disconnect is used between the provided power source and the pigtail from the machine . But a big zap of lightning could still make that jump in the switch. but if hit that hard there would be other issues as well, seen it quite a few times when live in FL. worked in utilities.

[William C Rogers]

it would have some disadvantages for sure if needed to be moved often. but most heavy equipment is hard wired and a manual throw disconnect is used between the provided power source and the pigtail from the machine . But a big zap of lightning could still make that jump in the switch. but if hit that hard there would be other issues as well, seen it quite a few times when live in FL. worked in utilities.

I still plan to unplug the lathe as I always do. The switch would only be used in an emergency condition. Strange thing yesterday as I had a 13" spalred maple bowl 2nd turning and dry 11% MC. I had turned it to about 1/2" thickness and stopped the lathe to check. I was turning the inside and there was some tearout so I figured I would put some sanding sealer and sharpen my gouges. As I was putting the sanding sealer on all of a sudden "SNAP" and it cracked from the rim to the base just sitting there. I didn't see any indication of a flaw. I can only speculate if turning I would have seen a big chunk come off and I would have been on the tail stock end and need to shut the lathe down.

Glenn, I don't have any friends that I know of capable to wire the emergency stop.

[Robert Edington]

Since no one else knows for sure, I'm safe to add my 2 cents.
First.You should unplug your VFD after every use. I don't care how long you've been lucky. I lost my PM 3520 due to a lighting surge.
Second. Circuit breakers are not switches. Don't use them to shut stuff off. Plus, that won't protect you from a surge.
Third. There is a thing called a sand resistor which absorbs energy created by the motor during braking. The sand in it absorbs heat. As Roger says, it's in the circuitry of the VFD. The sand resistor is a protector for the motor and VFD. I think if you disconnect the power as you propose, you'll bypass this safety feature which protects your equipment. In spin down, the motor becomes a generator.

If I'm wrong about this, I apologize in advance.
RP

[John K Jordan]

...You should unplug your VFD after every use. I don't care how long you've been lucky. I lost my PM 3520 due to a lighting surge.


Visiting my son this week end - he said when a thunderstorm threatened he started unplugging everything in the house. He had just unplugged the last "device" when lightning hit. The only thing it fried was the ice maker on his fridge which he didn't think to unplug. A neighbor lost multiple TVs, iPads, audio equipment, computers - basically almost everything plugged in.

JKJ

[William C Rogers]

Since no one else knows for sure, I'm safe to add my 2 cents.
First.You should unplug your VFD after every use. I don't care how long you've been lucky. I lost my PM 3520 due to a lighting surge.
Second. Circuit breakers are not switches. Don't use them to shut stuff off. Plus, that won't protect you from a surge.
Third. There is a thing called a sand resistor which absorbs energy created by the motor during braking. The sand in it absorbs heat. As Roger says, it's in the circuitry of the VFD. The sand resistor is a protector for the motor and VFD. I think if you disconnect the power as you propose, you'll bypass this safety feature which protects your equipment. In spin down, the motor becomes a generator.

If I'm wrong about this, I apologize in advance.
RP

If the way I propose it would just be a quick off then on that would reset the latched power on switch to off, so if the electronics sense heat it should bring the protection back on. In all reality I doubt this would ever be used, but realize the possibilities. I would think there have been instances where there is a brief power interruption when a VFD device is in operation.

[Prashun Patel]

I am unclear how if the VFD is unplugged before the fan has completely cooled is a problem. If the machine were going to be turned on in the next 5-10 minutes, then the fan would assist in accelerating the cooling between uses and during use. However, if the machine will be shut for the day, and the fan is interrupted mid-cooldown, then wouldn't the lack of power to it mean it's going to cool just fine in - what - an hour?

I might think the problem is the abrupt cutting of power to any electronics. However, I notice that when I unplug the lathe, the VFD remains powered for another 20 seconds, and the LED annouces a different mode, before finally clicking off.

I am not knowledgeable on this, so please lmk where I am being naive.

[David C. Roseman]

If the way I propose it would just be a quick off then on that would reset the latched power on switch to off, so if the electronics sense heat it should bring the protection back on. In all reality I doubt this would ever be used, but realize the possibilities. I would think there have been instances where there is a brief power interruption when a VFD device is in operation.

William, this actually highlights one of the biggest risks of a do-it-yourself double pole-double throw (DPDT) switch wired into the input 220v AC power side of the VFD between the 220v wall receptacle and the lathe. It sounds like that's what you have in mind, rather than wiring a switch into the low voltage circuitry of the lathe's existing switch. If the input power is cut off, but then cut back on as you describe, without waiting at least two minutes, you risk damaging the VFD. Here is an excerpt from an article by Thomas Robbins, a machine systems Applications Engineer, titled "Feed the Right Power to Your VFD." The whole article can be viewed and downloaded at http://www.machinedesign.com/motorsdrives/feed-your-vfd-right-power

Excerpt:

Do not cycle the input power more than once every two minutes. In fact, drive manuals specifically warn that switching a drive off and on without waiting two to three minutes is detrimental: Applying input power more quickly causes a buildup of voltage in the input pre-charge circuit, and eventually burns it out. Why? Here, the dc bus capacitors don't have enough time to discharge, and the input circuit needs time to stabilize. Otherwise, additional input can damage the charge relay circuit, or at the very least, blow the input fuses or circuit breaker.

In other words, the pre-charge circuit allows a certain time limit for the inrush limiter to send current through to charge the dc bus capacitors. The inrush limiter resistance changes with temperature. The hotter the limiter gets, the lower the resistance value. When that pre-charge time ends, the relay cuts off and the capacitors hold the charge. When the drive is powered down, this voltage bleeds off through resistors in the discharge circuit. Power reapplied too quickly meets an inrush limiter that hasn't had time to cool down to an acceptable resistance level, so the current will be higher, and consequently, could blow the fuses or possibly damage the pre-charge circuit.

The problem that Robbins describes is in addition to the two that others have already mentioned: Interrupting all power to the lathe (1) defeats the VFD's cool-down cycle, and (2) defeats any built-in dynamic braking feature, thus causing the lathe to go into free-wheel.

In an emergency, stopping the lathe is the important thing. If you can't reach the lathe's built-in E-stop switch safely, then of course pulling the plug, flipping the circuit breaker, or using a do-it-yourself 220v DPDT switch is better than nothing. But we should be aware of the unintended consequences. BTW, if we happen to be turning at the time of a power failure, the loss of the cool-down cycle and the dynamic braking feature occurs then, as well. And if the power comes back right away, the risk of damage that Robbins describes exists. But occasional power failures are pretty much unavoidable. Even if an automatic back-up generator system is in place the risk exists absent a very sophisticated setup, as the cut-over to standby power will likely involve delay and voltage swings. Robbins discusses that in the full article.

I'm not a sparky, but bottom line for me is that a remote switch intended for use as a "start/stop" switch, rather than simply to shut off all power in an emergency same as pulling the plug, should only be wired into the lathe's existing low-voltage start/stop circuit.

Evidently none of this came up in your conversation with the Laguna customer service person. Perhaps he/she was only thinking in terms of an occasional shut-down of 220v input power while the lathe is operating, so didn't see a risk of damage to the VFD as a practical matter. And of course pulling the plug after the lathe has been shut down properly is not a problem at all.

[Roger Chandler]

Wonderful information, explaining the technical aspects of all this David! Thank You so much for reliable information that helps us protect our hard earned investments in our machines. :)

[William C Rogers]

David, I also appreciate your in depth explanation. So I have decided not to install any remote. Although very unlikely, if the situation arose I will use my headstock emergency switch. I will figure out a way to engage it without putting myself in harms way. I have never had a situation where I needed a remote emergency stop and suspect this is a rare occurrence.

[David C. Roseman]

Roger and William, as I say, I'm not an EE, but I have looked into these issues. I'm just passing along wisdom from folks who are and know these things.

Putting a do-it-yourself DPDT switch in the 220v input line is an easy and tempting way to kill all power to the lathe (or other equipment) in an emergency. There are 220v DPDT magnetic switches, even "paddle" or "knee" switches, available online for under $15. I know of turners who have done this. When a VFD is involved, though, we should be aware of the other considerations.

If one is used, I suggest thinking of it only as a substitute for "pulling the plug", and making sure anyone who uses the lathe knows why. If under the circumstances you would pull the plug, use the switch. So, if the lathe is actually operating, that means only in an emergency, never merely as a convenient way to shut down the lathe. But even then, be sure to wait two or three minutes before flipping the switch back on. Absent an emergency, I would use the switch only after the lathe has been shut down normally and you want to disconnect from the line power to avoid damage from power surges. In the latter case, though, a DPDT switch only disconnects the two hot legs, not the ground leg. So a lightning ground strike might conceivably reach the lathe anyway. And even with respect to the hot legs, the disconnect is only the gap between the switch contacts. Pulling the plug from the receptacle would still seem to be the best protection.

[John K Jordan]

DPDT switch in the 220v input line ...
If one is used, I suggest thinking of it only as a substitute for "pulling the plug",...

That's how I use mine - turn off the lathe with the control switch, then throw the switch when leaving the shop. I'd like to replace it with a 3-pole single-throw switch to include the ground as you mentioned but I've never found one - maybe a 3-pole contactor instead. BTW, I you should only need a DPST switch but the double throw doesn't hurt anything.

[David C. Roseman]

[snip]
BTW, I you should only need a DPST switch but the double throw doesn't hurt anything.

Good point, John. I should have said DPST, otherwise the throws would have to come tied together, as on a typical 220v circuit breaker. In fact, the inexpensive magnetic paddle switches I mentioned are DPST.

[Glenn C Roberts]

John, Can you use a 3 phase DPST?

[John K Jordan]

John, Can you use a 3 phase DPST?

I've never had one in my hands but I don't see why that wouldn't work! Duh - I had searched for "3-pole" but never thought to search for "3-phase power switch" - now I see lots of options. Thanks!!

Due to the contact separation issue mentioned earlier it still might not help with a local lightning strike but then there's not much that will other than unplugging. Should be perfect for moderate power line surges though. Fortunately, all the power lines on our farm are underground.

JKJ

[Bruce Schoenleber]

Would a near ground strike (lightning) still charge the ground wire sufficiently to fry a VFR? I too have below ground utilities but still unplug my lathe for just that fear. I would prefer the 3-pole switch solution. My paranoia stops short of wrapping my shop in lead in case of a Solar Mass Ejection, how cavalier is that? ;)

[John K Jordan]

Would a near ground strike (lightning) still charge the ground wire sufficiently to fry a VFR?

That's a good question. I was told that the underground wiring helps. Maybe someone who lives on the top of a hill will volunteer to put up some lightning rods and test this!

My power is 600' underground to a 7200v transformer near the house, then split about 75' underground to the house on the top of the hill, 250' to the shop, and maybe 2000' to a shed, barn, and electric gate. We've had several "good" lightning strikes following trees to the ground but I've not yet had anything fry. One time the 7200v underground feed went out with a pinhole in the insulation - the utility guy said it may have been from lightning but he didn't know. That blew the fuse on the pole at the property line as did once in the past when termites got in under the transformer - when the fuse blows it sounds like a cannon going off!

I did have a VFD go bad once but it was a gradual failure. I don't think it was from a power surge but it was during those years when I left the lathe plugged in all the time.

JKJ

[JohnC Lucas]

I haven't read this whole thread (it's quite long) There seem to be 2 issues here. One is disconnecting the lathe from the power source (unplugging) and the other is a remote switch. The switch that turns the lathe on so it spins I will call the power switch. Those are usually hooked into the VFD and are low power. The 3 phase simply goes from the VFD to the motor. You never need to switch that, it's done internally in the VFD. The power switch is hooked directly into the VFD and simply tells the VFD to turn the 3 phase on or off. Very easy to put a remote switch in to turn the lathe off. The other switch is I will call the main switch. This is the switch that applies the 220 single phase to the inverter. Like John I turn the circuit breaker off each night. On my powermatic if you leave the main power on the VFD stays on or has power. I turn the circuit breaker off for two reasons. One is to disconnect the power to the VFD and the other is to try and protect it from lightening strikes and power surges. I've been doing this more than 12 years now and my lathe still runs perfectly. (Powermatic 3520A) I also did this on my Nova 3000 that I added a VFD to. No problems.
I hope I didn't miss some important issue in the other threads. I know John K knows all of this already.

[Bruce Schoenleber]

What caused me to ask is that there is always (or should be...) a 5-6' copper ground stake near the main power panel. That is where I would expect to pick up the surge from a strike.

[Dick Strauss]

Just so that we are all clear here...the emergency stop button interrupts a 12-24V (maybe 0.01-0.1A) DC signal between the VFD and itself. If the VFD doesn't see the signal on its inputs, it shuts off power to the motor. You can wire another switch in series with the e-stop where both have to be on for power to the motor. You can also wire one switch in parallel with the existing e-stop whereby the motor will be receiving power if either or both switch(es) is/are on...

For protection from surges and strikes you want to interrupt power between the incoming wall power and all conductors (including the ground) to the VFD. A three phase disconnect will do the job but unplugging is better because lightning can jump a gap in a switch! The more distance the electricity has to jump, the better protection you have.

[Olaf Vogel]

Hey Brice,

IMO it problem is a lot simpler than you think.

Ideally what you have is:

One central power panel that distributes to all your machines (Including the VFD's)
At the end of the day, hit the main panel and disconnect everything. That insulates against power surges etc.

One circuit breaker for each major machine. This is required, by law, in industry. Commonly known as a disconnect switch.
I use these for 3 phase: https://www.ebay.com/itm/CHNT-Triple-Pole-3-phase-AC230-400V-2A-Circuit-Breaker-Din-rail-mounting/301845858116?hash=item46476a4744:g:w74AAOSwYIhWlMD 8

There are single phase versions.

Whether your shop is single or three phase - its all the same idea.

To shut down your lathe, hit stop or emergency.
Wait about 30 sec, disconnect it - either via the disconnect switch or the main power.

I have 6 VFDs in the shop, from 1 hp up to 10 hp.
Thats been my setup for 5 years now - installed by an industrial electrician. Never had an issue.

And the shop is in a rural area where brownouts are common.
Plus I have a steel roof, which must be lightning friendly....

[Olaf Vogel]

I've never had one in my hands but I don't see why that wouldn't work! Duh - I had searched for "3-pole" but never thought to search for "3-phase power switch" - now I see lots of options. Thanks!!

JKJ

John

I think you have two options:
https://www.ebay.com/p/Never-GE-Heavy-Duty-Safety-Switch-TH3362R-600-VAC-60-a-3-Pole/1600001876

These are huge, heavy, expensive and the fuses are a one shot deal.
The best of 1920's technology, wickedly overpriced.

or the European solution
https://www.ebay.com/itm/CHNT-Triple...4AAOSwYIhWlMD8 (https://www.ebay.com/itm/CHNT-Triple-Pole-3-phase-AC230-400V-2A-Circuit-Breaker-Din-rail-mounting/301845858116?hash=item46476a4744:g:w74AAOSwYIhWlMD 8)

Get a 4"x4" distribution box from Home Depot and cut a square for the switch

Cheap, easy to reset, small.


Guess which ones I use?
:)

[Don Bunce]

Olaf, Those breakers are only rated at 2 amps. I would think that you would need something like 20 amps.

[Olaf Vogel]

Olaf, Those breakers are only rated at 2 amps. I would think that you would need something like 20 amps.

Sure, I meant that type. They go from 2A up
https://www.ebay.com/itm/CHNT-Triple-Pole-3-phase-AC230-400V-20A-Circuit-Breaker-Din-rail-mounting/381490452963?hash=item58d29a59e3:g:aUQAAOSwfZ1WbBj k

Pick the size you want