VFD keeps tripping GFCI

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?

VFDs often have enough leakage to ground to trip a GFCI that's working properly.

The instruction manuals for my VFDs even include a specification (> 3.5mA) and discussion of that fact.

As Bill said, you should use 240v AC for your machines, regardless of whether you use a VFD or not.

- Leigh

If unfinished area then install an outlet overhead in the rafters and use a twistloc.

Label it lathe.

Make cord for lathe that matches.

Was surprised to find that the latest code does require GFCI outlets in a garage ("All 125-volt, single-phase, 15- or 20-ampere receptacles installed in garages and grade-level portions of unfinished accessory buildings used for storage or work areas shall have ground-fault circuit-interrupter protection for personnel.")

Note that it is only 120V circuits, so Bill's & Leigh's solution would in fact solve your problem. I also found an ABB publication that said some interesting stuff, and suggests RFI/EMC filters might help. Maybe someone else can suggest exactly how to do that if you for don't want to add a 240V outlet and buy a new VFD (unless yours allows 120v & 240V single phase input).

Here's the text of the PDF:

Description: Can a GFCI circuit breaker be installed on the AC power feeding a drive, or will the drive cause it to trip?

Answer:

The AC Drive most likely will cause the GFCI protection device to trip. The reason the AC Drive
will cause this tripping of the GFCI is the Common Mode Current or Common Mode Noise (CM
Noise) that the VFD is producing. The high rate that the IGBT is switched on and off is around
(1 - 16 kHz). This switching creates Common Mode Electrical Noise. The Common Mode
Noise is the current that appears on a conductor with respect to ground. This Common Mode
Noise can and will travel throughout the plants ground system and even beyond. This Common
Mode Noise can affect the operation of the application, and other equipment in the plant by
interfering with signals from sensors, computers, PLC’s, telephone and radio. The VFD does
provide ground fault protection on the output of the VFD.

Corrective Actions:

The goal is to have all the Common Mode Noise return to the VFD. Here are some actions that
will help reduce or eliminate the tripping of the GFCI. The motor cable should be VFD rated
motor cable and the motor and shield should be grounded back to the VFD. The User Manual
will provide information on how to correctly install the VFD. The installation of RFI/EMC filters
before or inside the VFD. Installing an isolation transformer before the VFD and after the GFCI
circuit breaker will help reduce the tripping of the GFCI.

Jeff

When it comes to having serious machinery running... solid-state drives, power supplies, radio transmitters... ground potential rise from lighting, nearby electrical substations, heat treatment ovens, arc furnaces... the answer is short and simple: GFIs suck. The best ones don't suck as much, but they all suck.

'the code' requires them, even where it is totally illogical, unsensible, and imprudent to do so, but The Code also absolves itself from liability by identifying itself as 'not law'... and that the NFPA is in no way liable one way or the other for what anyone does, or does not do.

I had an inspector demand that I install GFIs on my home's sump pumps. I've tried a dozen different brands of GFIs, and EVERY one of them will trip... EVEN with NOTHING CONNECTED, each time there's a foggy day. Why? Because I'm 750 feet from a 35,000w FM broadcast tower... the wiring in my house is subject to some substantial radio energy from that, and substantial ground-potential rise from the atmospheric interaction with that tower, and the power feeding my home. Henceforth, my choice, was to either be compliant, and go without sump pumps, or be compliant, allow the pumps' GFIs to trip, then allow the basement to flood to the level of the outlet (remember- just because the GFI trips, doesn't mean the backside wiring isn't hot)... and flood the water heater, furnace, or just be non-compliant, and have a dry and safe basement.

I agree with the others- pull a 240 feed out... even if it's low power, put in drops for 240v/20A plugs and call it good.

Thanks everyone. Right after I posted this and started researching more I did say to myself: "This is stupid. If I just put in the 240 I don't have to worry about this crap." So, that's what I'll do. Sucks that I just bought the 115v VFD, but I'm sure I'll be able to sell it without a huge loss, hopefully.

A serious line filter on 240V balanced (not UK 240) will actually have much of the leakage current balanced out and not affect the GFCI. A fair amount of the switching-induced current from the VFD frequency will probably be balanced out also. A better filter will fix a lot of that even better, though.

THAT is the reason to use 240V. That and the fact that 120V is so power limited.

Did you mention the motor power? Didn't see it. Another reason is that even 1 HP is a serious drain on 120V.... Especially with a VFD and its addition to the bad power factor of the motor.

Stronghold said:

Thanks everyone. Right after I posted this and started researching more I did say to myself: "This is stupid. If I just put in the 240 I don't have to worry about this crap." So, that's what I'll do. Sucks that I just bought the 115v VFD, but I'm sure I'll be able to sell it without a huge loss, hopefully.

Click to expand...

Wire up your 240 outlet with a receptacle that can do both 120 and 240... like a NEMA 14-30 dryer outlet. Then configure your plug to power the VFD that you already have to just tie into the 120 part of it. Or just toss the GFI. I am with Dave K; although they have some rational basis in 100% civilian settings like bathrooms and kitchens, around swimming pools, etc., they are an abomination in working settings. Deliberately don't have them in my workspaces.

Thanks again everyone. The motor is 1 HP, 3.9 amp. I checked my panel and only have enough room for one 240v breaker. So I'm not sure what I'm going to do when it comes time to get my mill up and running when I'm done with it.

Stronghold said:

I checked my panel and only have enough room for one 240v breaker.

Click to expand...

You actually have room for a bunch of 240v breakers.

Replacing one of your full-width breakers with a pair of half-width breakers frees up on full-width slot.

- Leigh

You can replace the panel with one with a larger load center and more breaker spaces. You could use the one existing two position space for a 240VAC breaker to power a rotary phase converter and power all of your machine tools of the rotary phase converter.

Vlad

The real Leigh said:

You actually have room for a bunch of 240v breakers.
Replacing one of your full-width breakers with a pair of half-width breakers frees up on full-width slot.
- Leigh

Click to expand...

Well that depends, the loadcenter needs to be listed for use with "twins" half width. Small loadcenters, like 20CKT are not usually listed for this use. Larger panels, like 42 CKT are usually listed for this use but limited to the slots that are approved, normally only the lower slots in the panel. The only way to be sure is to check the label inside the panel door. Most newer loadcenters and breakers will have a rejection mechanism built into the buss assembly or breaker design to limit where they can be placed to enforce the rule.

Sound's to me that the OP needs to use the available remaining slots to power a subpanel in the garage, for his future shop setup, can be expensive but worth it...

SAF Ω

Another simpler alternative since you already own the VFD, get rid of the plug and hard wire it. The rule only applies to receptacles, not hard wired machinery.

Yes wire up a new line, but...

I had exactly this same problem.
1HP VFD on a 120V line with a "cheap" gfci from Home Depot.
The gfci would trip 50% of the time.
I replaced it with a more expensive unit from a proper electrical supplier.
Has not tripped in 2 years.
Much cheaper in a situation where I had the VFD, and all the wiring was done and in place.

Josh

Or you could even install a 5-20P plug on the VFD, and install a matching receptacle... that solves that problem... ;-)