# VFD keeps tripping GFCI



## Stronghold (Jan 19, 2015)

First off, I want to let everyone know up front that I'm an electrical noob of the highest order. I picked up a South Bend lathe and an Ex-Cell-O mill, both of which have 3 phase motors and are located in my garage. I hooked a VFD up to the lathe that's meant to run off of 115v single phase which is all I have in the garage. I've got everything wired up with 12 AWG cord and when I plug it in the VFD turns on just fine. When I hit "run" the motor will spin for a second and then the GFCI trips. I can reset the GFCI and the VFD turns on again just fine and then trips again when I try to run the motor. 

From my research it seems that this is a common issue with VFD's, and people usually just replace the GFCI receptacle with a standard one and everything is good to go. Now, from my understanding I must retain GFCI's in my garage in order to remain compliant. Does anyone know what I can do to fix this annoying issue while staying compliant?


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## JimDawson (Jan 19, 2015)

The only thing I can suggest is to make sure you have a good ground between the motor and the VFD, and that the VFD is properly grounded back to the plug. 

Failing that, the only option may be to replace the GFCI with a standard plug, but that would put the installation out of code.  I am not going to advise you to do that.


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## Jim Nunn (Jan 20, 2015)

Jims suggestion is a very good one. Lack of proper grounding causes all kinds of problems with drives.

The GFCI fault is indicating  that  ground exists in the output of the drive.  All drives check for a ground path on the motor leads as part of the start up for the simple reason that this could cause the output IGBT transistors to turn into 3 wire fuses.   Disconnect the motor at the drive and start the drive and see if you are still getting a ground fault, if you don't then it's a high probability that the drive is good. 
If it does not then reset the drive to factory defaults it's a long shot but this could clear the problem.

If it does pass this test then check all connections between the drive and the motor looking for poor connections or loose wires.  Open the terminal box on the motor and triple check the connections.  If wire nuts were used unscrew them and check the wires use new wire nuts and tape the motor leads.

look for any switches or controls between the drive and the motor these should be eliminated.

Make sure that the motor is wired for 230/208 not 460 there should be a wiring diagram on the inside of the motor terminal box cover.   Not knowing the age of the machines if they have cloth covered wire then you have to rewire the machines using new wire.

As another way of checking the drive connect it to the other machine and see if faults out.

Jim Nunn


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## mksj (Jan 20, 2015)

You may be exceeding the GFI's current rating when the motor starts, usually most 120V GFI's are 15A. *You can replace it with a 20A GFI only if the circuit/outlet is protected by a 20A or larger breaker and wiring to the socket is at least 12 gauge*. There are also GFI breakers, but must be sized to the wiring and circuit, and you need to know how to properly install them. You could also try a slower acceleration speed or acceleration ramp on the VFD programing.

I have also had GFI's go bad (tripping or not resetting) and needed to be replaced.


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## Eddyde (Jan 20, 2015)

I agree with all the above. However, if none of those suggestions fix the problem, you may need to run another circuit from the panel to the garage. In that case it would be a dedicated machine circuit and would not, as far as I know, need to be GFCI protected. That would also give you the opportunity to make it a proper 230v which would be better for running the VFD and the machines, anyway. Of course, double check your local codes beforehand.


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## countryguy (Jan 20, 2015)

I'm sure I missed something here but how do you get a 110VAC GFI into a 2phase input VFD to make 3 phase output poles.   Do they make those?   I read it 3x.  I'm not getting it?   Or did I get something wrong and 1 leg of 220/240 has the GFI?      My head is hazy still from the expensive spend on my new ajaxCNC setup.....  Uggg.   What this site hath done to the poor city guy moved to the county and just wanted to make a plate or two for his tractor......


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## JimDawson (Jan 20, 2015)

countryguy said:


> I'm sure I missed something here but how do you get a 110VAC GFI into a 2phase input VFD to make 3 phase output poles.   Do they make those?   I read it 3x.  I'm not getting it?   Or did I get something wrong and 1 leg of 220/240 has the GFI?      My head is hazy still from the expensive spend on my new ajaxCNC setup.....  Uggg.   What this site hath done to the poor city guy moved to the county and just wanted to make a plate or two for his tractor......




120 single phase in, 3 phase 240 out.  These have a voltage doubler circuit in them.  http://www.automationdirect.com/adc...ts_(115_-z-_230_-z-_460_-z-_575_VAC)/GS2-11P0

Voltage doubler:


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## countryguy (Jan 20, 2015)

Tada.... Forrest Mims would be proud!  OK.  Thats an easy concept and I've used them in the past.  Long past but nice to see them still being productive.   OK,  so it's easy enough.  

As for grounding-  Been doing some reading on the code and Neutral bonding to ground.  Not always done right.  Ground loops from building to building and Ground from the Pole (Provider) to the main.   ground is a PIA if not done right.   I believe in GFI's-     Lots to check it seems. 

Plus I sunk an 8ft rod into the ground myself and have been looping things like all the Plasma and CNC stuff to that ground as well for chassis and such. 

   ;-)   Ohh what fun!   Thanks Jim!


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## countryguy (Jan 20, 2015)

Honestly I had not ever researched how these work.  Here's a good review and offers tips on constant tripping.  A good one for the masses. (well me anyway).
http://www.nema.org/Products/Documents/NEMA-GFCI-2012-Field-Representative-Presentation.pdf


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## Jim Nunn (Jan 21, 2015)

I maybe missing something do you have a GFI if front of the drive on the incoming leads?   I'm assuming that the drives built in GFI is giving you a fault and what I suggested is based on the drive indicating the ground fault.


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## chhedausa (Jan 21, 2015)

I am having the exact same problem with an automation direct gs1-10p5 vfd.  It is also on a 20 amp gfci.  I called AD to troubleshoot and they said that most likely something got fried on the vfd.  I just got in a new one and I am about to wire it up.  I will report back the results.


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## chhedausa (Jan 21, 2015)

I just tested and I am getting the same problem with the new VFD.  I ran it on a new GFCI I installed on the other side of my workshop that is on a new breaker and it works.  I think it may be just a worn out receptacle or maybe the old wiring is not sufficient.  I do not know.  I really do not know enough about wiring and electricity to determine the issue.  I am going to try to replace the old GFCI outlet with a new one.


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## Doubleeboy (Jan 21, 2015)

I would bet that removing the GFCI completely would solve your problem assuming all wiring is hooked up correctly.  Unless you are going to be standing  barefoot on a wet floor holding a a metal framed electrical appliance I fail to see the need for the GFCI.   I have been in dozens of shops and I dont ever recall seeing one, except in the bathroom.
Michael


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## CluelessNewB (Jan 21, 2015)

I have had several GFCI receptacles fail tripping for no reason.  Rather than replace with GFCI receptacles I have gone with GFCI breakers.  They cost a bit more but seem to be better built and I haven't had one fail yet.  You can buy a GFCI tester for about $8-$15 online or at Home Depot, Lowes etc.


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## chhedausa (Jan 21, 2015)

I figured it out.  It was the GFCI outlet that was the problem.  I did have it loaded with 15+ amps with other machinery and it would not trip, but with only the VFD it would trip, which is only about 9 amps.  Not sure what the exact problem was, but I replaced it with a new one and the VFD is running on it now.

Now I have to get a motor for the extra VFD I bought.


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## mksj (Jan 21, 2015)

Actually the GFI will not trip if overloaded per se, but the GFI imbalance with load may increase causing it to trip. Needless to say, I have had them just go or get finicky with time. I have had better luck with the 20A versions, and it is is acceptable with my 12G wiring. It is important to install them with the line load direction correctly, and the neutral is not grounded after the breaker. I do recall some problems using a GFI with VFDs, not sure how this mingles with the residential electrical code in the garage location. Anyway, this is a short review of some possible corrective techniques to decrease the interaction between the devices. http://www05.abb.com/global/scot/scot239.nsf/veritydisplay/bbe3c864d311f0e88525792000750ed3/$file/LVD-EOTN14U-EN.pdf


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## jim18655 (Jan 21, 2015)

Some GFCI receptacles are more sensitive to RFI than others. Some will trip from operating ham radios in the area. I once worked on a house that had a back-up generator that tripped all the GFCIs in the house when it started. The motor or drive could be generating noise back into the GFCI. My Grizzly mill won't run on  GFCI receptacle and it's relatively new.
One thing I would check is to make sure there aren't any connections between the ground and neutral in the control box. At one time a machine, even the stove and clothes dryer in your house, was allowed to be grounded to the neutral wire. Check with an ohmmeter between the neutral and ground on the machine for continuity. There may be a light connected from the hot to ground if there isn't a neutral available. It only takes 5mA to trip a GFCI, not much more than a flashlight bulb.


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## CoopVA (Jan 21, 2015)

I had the same issue.  Replaced the GFCI breaker with a regular one and never looked back.


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