Machine blows my GFI

For some reason, my MK2 blows my GFI. At first, I thought that the power strip was bad. I replaced the power strip with a brand new power strip and it still happens. Any suggestions? I have moved it to a dedicated circuit with only a single GFI on it and it still does it after jogging the MK2. Any suggestions would be greatly appreciated!

@Jake If you put a similar load on the GFI using another appliance, does it behave?

Hi Grant!
Yea both circuits are just fine. I have run my cabinet saw on both circuits without issue. Thinking before I start a ticket, I will unplug the motors one at a time and see if it is a motor or cable to a specific motor. I tend to have decent trouble shooting skills when it comes to electrical. My bet is something happening inside the control block. But i could be wrong too. I did notice it pops the GFI while sitting idle.

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So I just unplugged all the motors from the control brick. It made it about 2 minutes and blew the GFI again. The only thing plugged in was the Power Button and the USB plug I bought from Sienci. I will unplug it from the control brick and see if that makes a difference. I will also unplug the power brick and see if that is the issue.

@Jake Are the PC and monitor plugged into the same GFI, too?

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@gwilki Hey Grant, I am using a MacBook Pro for the control computer. Yes it is plugged into the same circuit. I unplugged the USB plug and it blew it. The last thing was to unplug the power brick from the Control Box. It did not blow the GFI, although there obviously isn’t a load on it either. Just for the heck of it, I will plug the laptop into a separate circuit and see if the issue is recreated.

I attempted to call Sienci and got their machine. I sent them an email outlining my trouble shooting and what I think is the issue. I will let you know what they say when they respond. Thanks Grant, I am excited to work through my issues and get carving!

@gwilki Hey Grant, found the issue. It is the computer plugged into the same circuit as the cnc. Really doesn’t solve the problem, probably a small current leak on the cnc control box or power brick causing the gfi to blow. I am fortunate enough to have a second circuit in close proximity to my router to plug into. Not all people would be that fortunate. I will update the service ticket so tech support can look a bit closer into the issue. Good call, would have never thought that.

Onto next problem. Thanks again sir!

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Let me start by getting the terminology straight here. GFIs do not blow, they trip, as they are designed to do if there is a different of current detected between the hot and neutral wires being supplied by the GFI.

If you run the laptop on battery power and you don’t trip the GFI, then that’s a pretty good indication that your computer power supply is what is causing it, not the CNC.


@Ranchdude appreciate the correction, thank you! This morning I did a couple of other things. This vintage Mac came with a 2 prong travel plug and a 3 prong “home” plug. I located the 3 prong plug and placed it on the power brick for the Mac to see if that takes care of the tripping issue.

I also downloaded the newest version of gsender onto an old windows based laptop I was originally going to use for control of the cnc. The windows laptop failed to connect so I went back to the MacBook Pro with the 3 prong power cord. I will see if it trips the gfi. Again, thank you! I have a punch list of issues and feel better getting through at least one of them.


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@Jake Since you had hoped to use the windows laptop for the CNC, maybe we can explore a bit why that is not working out. What OS are you running on it? When you say that you cannot connect to the Mill with it and gSender, does Windows see the comm port at all in Device Manager?

@gwilki Thanks Grant, I appreciate that. I want to pick my battles now. I want to get the machine up and carving. The windows laptop runs windows 7… It was new in 2008. The Mac runs and runs good. For now, I think I should just stick with it, especially now that I have the GFI problem solved. I am incredibly happy that it wasn’t a control board or a power brick. That would have pushed me back and I want to get carving! I have some things from Jason to try and fix my other two punch list items. If they don’t work, I will post my issues here and see what the board has for solutions. Have a great afternoon sir, you are fantastic to have around for sure!

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What causes a GFCI to trip is an imbalance between the neutral and power line when a connection to the ground line occurs.
Your fault will be in the AC circuit. You’ve provided a dedicated line which is good. Double check the outlet box and verify the grd line is seperated, if it touches neutral (white) this will trip it.
How do you get power from the wall to the CNC? If you’re using an extension cord, try a different one.
Try moving item’s plugged into the power strip one at a time to a seperate source, this will isolate the one that causes the trip.

@Bruces-CNC Thank you for the help. I still get the occasional GFCI trip. Going to move some things around in my shop and see if that helps. I actually found the first thing I would change if I were to rebuild my shop. I would mix outlets, meaning not having an entire wall on one circuit. My CNC machine and table saw are on dedicated circuits however. That seems to help quite a bit in itself.

Thanks again for the info, I greatly appreciate it!


Your are correct a GFCI trips when sensing a fault. You are wrong a GFCI can blow when it sees a catastrophic short to ground in a device or appliance connected or serviced by the device. At that point the GFCI is no longer serviceable and can not be reset.

As to the posters issue. He is experiencing an arc fault most likely from the laptop power source or and the power brick for the CNC controller. This was one of the issue that resulted in the newer AFCI Receptacles and breakers being created. Many laptops had this issue in the early 2000 and had to do with the circuitry used. Sometimes a small popping sound can be heard when plugging in a power brick. That is an ARC occurring. Does this still occur in newer laptops or power sources used on said devices that use for lack of better terminology power bricks. Yes a very sensitive GCFI or AFCI or a combination of both will trip. Also a bad battery in a laptop will cause an overdrawing of the charging circuit also tripping or triggering the GFCI/AFCI . I hope this brings some clarity. If needed I can upload a photo of a 20 amp GCFI that is blown from catastrophic short to ground due to water getting on the circuit board of an appliance control module.

Thank you! I am still moving battery chargers around my shop. I did notice that since unplugging them 3 Dewalt chargers, I have not had any gfi trips. Even with the laptop still plugged in. Strange for sure. Never had the problem before the CNC. But then again, never had the laptop out there either. Difficult to troubleshoot for sure.
Thanks again!

You are most welcome. Like you my Cordless tools battery charging stations are located in my shop. I do occasionally use compressed air to clean and blow woodworking dust and debris out of the chargers.
Years ago I came accross a crazy short to ground on a circuit board. Then 120vac fuse keep blowing. I tested all power points an there were zero pathways to ground. I was stumped and pulled the circuit board. To inspect the board under scope. It was when I turned the board over that I found a spider on the back of the board. It was the damndest thing. That spider was fried between 2 contact points. When the board went through the power up sequence it would finally power those points an the spiders body would provide the short. But would not show up on an omhs test due to internal circuit on the logic circuit of the board. I cleaned the board with contact cleaner. Reinstalled and all was good. It was the first time I worked on a 100 ton HVAC unit. It was that simple thing that took down the manufacturing plant as the unit was the main cooling unit integral to making specialized paper. Since then I take a little time to clean all my tools, computer intakes, open housing air vents on any large/small woodworking tools, because that lesson taught me that something minuscule can stop all work from occurring.
I put all my battery chargers on a surge strip that provides equal power to each Receptacle. Plus it suppresses any harmonic imbalance and electrical noise as several of my machines do have digital control and electrical noise does cause interference. Being that i live in very rural area with old infrastructure issues do sometimes arise. It sometimes shows itself when I plug in my radio in the shop I get feedback noise when running certain tools.