# New GFI 110v outlets blow out TECO VFD



## Glenn Brooks (Jan 29, 2018)

I decided to install three new 110 v outlets at my grinder bench to accommodate my power tools.  The county electrical code requires GFI outlets when any upgrades are accomplished, so I installed 3 GFI outlets.

Now my baldor 8” grinder doesn’t work. It is powered with a Teco L510 110 to 220 3 phase  VFD. when I push the on button, the VFD powers up the grinder for maybe 2 or 3 seconds, then the  gfi circuit trips and the grinder goes dead.  

Of course, with the old standard plugs, the VFD and grinder work just fine.  But the electrical inspectors won’t sign off on old style plugs, demand GFI’s.

Any one advise me how to fix this?  Maybe some parameter in the VFD?

thanks
Glenn


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## rwm (Jan 29, 2018)

I was always told not to use motors on GFI circuits. I am curious to hear the experts replies on this. Do you have to use GFI receptacles or can you use GFI circuit breakers? Would one work better than the other potentially? (by potentially I don't mean electrical potential I mean theoretical potential or hypothetically....oh, never mind.)
Robert


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## markba633csi (Jan 29, 2018)

Do you have a good earth ground on the Baldor separate from the one in the power cord?  What about the Teco ground? Robert has a good point; maybe the GFI breakers are less sensitive than the outlets
Mark S.


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## jim18655 (Jan 29, 2018)

GFCI or AFCI?  AFCI is required by NEC in almost all new applications. GFCI in some applications. My Grizzly mill wouldn't run on the code required GFCI (unfinished basement) and a call to tech support was not much help.
Somehow some of the power to the drive isn't getting back or, the more likely reason, the drive is creating some interference that trips the GFCI. Ask any ham radio operator about some GFCI or AFCI devices tripping when transmitting. Try some ferrite cores around the power supply cord to the VFD.


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## Glenn Brooks (Jan 29, 2018)

Mark, the motor and VFD are bonded together thru the pedestal mount, but I do not have the motor or VFD grounded directly. They do ground thru the ground wire in the circuit coming from the main panel.  I can certainly run a separate ground wire directly to a grounding rod I installed just for this purpose.

Jim, these are common residential GFCI fixtures.  Not sure what an AFCI is...

In googling Teco VFD’S it appears many people say this is an insolvable problem as required GFCI receptacles sense differtial current and automatically assume a ground fault when none actually exists - if I am paraphrasing correctly.  So far, the fix seems to be, get the inspection signed off, then replace the da&n things with standard electrical outlets.


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## pdentrem (Jan 29, 2018)

Replace the 110 with 220 to avoid the GFCI issue completely. I cannot say what you should do after the inspection is signed off but there is mention of using the ferrite rings and to reduce the length of wire to the motor if possible and increase or actually attach the shield ground to remove EFI. Lots of chatter on the web about this and with the codes moving to more GFCI and AFCI is Arc-fault breakers for home use, issues will occur and manufactures have to step up.

https://library.e.abb.com/public/bbe3c864d311f0e88525792000750ed3/LVD-EOTN14U-EN.pdf


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## rwm (Jan 29, 2018)

Does an AFCI breaker also provide GFI safety?
If you hard wired the Teco VFD ( no receptacle) would the AFCI or GFI be required?
R


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## Glenn Brooks (Jan 29, 2018)

Well, I don’t have 3 phase in this area of my shop, so eliminating the VFD isn’t an option for me.  Hardwiring the VFD to the 110 circuit IS an option.  I’ll have to ask the county inspector if that is permissible under the code. Might be an excellent option.  

Thanks
Glenn


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## mksj (Jan 29, 2018)

You cannot use a residential GFI with a VFD, it induces current (leakage) in the neutral wire that will trip them every time. In industrial settings that require a GFI, you can buy a comercial one specific for use with VFDs and they are very expensive. An AFCI is not a GFI, although they do sell combination units, the GFI will still trip. I suggest you call Teco Tech., but I have seen this problem countless times and the only solution is to not have the VFD on a GFI outlet.
https://www.schneider-electric.us/en/faqs/FA274920/
http://www.bender.org/


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## TimSmith (Jan 29, 2018)

Glenn, you might find that the "leakage" that mksj refers to is caused by an RFI (or EMC) filter that is sometimes installed to limit radio frequency interference from the vfd, rather than leakage from the drive itself.  They have a connection to ground, via internal capacitors, which can pass enough current to trip the gfci.  I would agree tho' that hard wiring the unit would be the best option, preferably through an industrial type ground fault circuit breaker.
Cheers Tim


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## Ulma Doctor (Jan 29, 2018)

i replaced my GFIC outlet with a standard 15 amp wall plug to avoid any problems like this


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## 4GSR (Jan 29, 2018)

After the inspector leaves, change the GFCI plug out with a standard one. Just be sure to change it back if you sell the place.


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## markba633csi (Jan 29, 2018)

I think Tim nailed it- it's the VFD's darn internal RFI filter that looks like a ground fault to the GFCI.  Only other solution I could offer would be to use a large isolation transformer between the GFCI and the VFD.  But, see if you can hardwire the VFD in or, use Ken's solution 
I don't think adding another ground will help but you could try. 
Mark S.


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## rwm (Jan 29, 2018)

North Carolina only adopted 2014 NEC in 2016 (with amendments.) My entire house is out of code at this point. It was built to existing code at the time though. Point being, only you know when specific work was done and if it was compliant at the time it was done. 
R


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## Glenn Brooks (Jan 30, 2018)

Thanks all,  looks like hardwiring the connection is the best option.  FYI, this is a new circuit I am adding, ( one of two) so have applied for an electrical permit and can’t get away from passing a new inspection meeting the latest code requirements, e.g. the GFCI  receptacles.


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## Blackjackjacques (Jan 30, 2018)

Generally, most jurisdictions require GFCIs only in damp or wet spaces.  Garages, bathrooms, un-finished basements, etc are usually classified as damp or wet spaces. Shops may not necessarily be classed as a wet or damp space. If there is a means such that the motor housing or enclosure can get wet - say condensation for instance then you want a GFCI.  GFCIs are sometimes waived where the branch service is dedicated to a particular appliance. The interpretations for what constitutes "dedicated" can vary from jurisdiction to jurisdiction. In some cases the AHJ will accept a receptacle in immediate proximity to the equipment and labeled as such, in some it may be a screwy receptacle style and your appliance being the only item with a matching plug, and in some it means a hardwired pigtail. You can ask the AHJ and see what they will accept.  Residential GFCI devices are Class A devices, meaning that they protect against electrocution as well as damage to equipment.  Class A devices range from 4 mA to 254 mA of leakage, while industrial (Class B) GFCI devices are set to trip above 254 mA and do not provide protection from electrocution -- they only protect equipment.  The AHJ should not normally permit Class B devices in a residential application where GFCI devices are invoked. As Tim and Mark points out, an RFI filter at the VFD can supply sufficient leakage to trip a GFCI. In fact, many lighting dimmer devices can also trip GFCI devices.  An isolation transformer between the GFCI and the appliance (in your case the VFD) will thwart GFCI tripping as well as practically eliminate the shock risk -  but they are pricey.  AFCI devices only guard against arc faults and do not do what GFCI devices do. AFCIs will trip if connected to anything that sparks - say a motor using brushes for instance.  AFCIs are usually required where a receptacle is in close proximity to combustible material - like drapes in a living room, etc.  GFCIs work and have saved lives while I am not so persuaded for AFCIs.  If you have a damp situation with connected equipment, you want a Class A GFCI device even if the AHJ says you do not need it.


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## Eddyde (Jan 30, 2018)

Glenn Brooks said:


> So far, the fix seems to be, get the inspection signed off, then replace the da&n things with standard electrical outlets.



That is exactly what I would do .


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## higgite (Jan 30, 2018)

Glenn,

The quote below is from the NFPA website, authors of the National Electric Code. Most municipalities that I’m aware of (certainly not all) who even have a code, usually rely on the NEC. Like Blacjjackjacques said, you may not be required to have GFCIs for your new circuits. Has the inspector said that you do? If so, have you asked him to point you at the written code or county requirement?

Tom

https://www.nfpa.org/Public-Educati...re/Electrical/Electrical-circuit-interrupters
“GFCI protection is required by the 2017 NEC for newly installed and replacement 15 and 20 amp receptacles on kitchen countertops, in bathrooms, outdoor areas, unfinished basements and crawl spaces, garages, boathouses, laundry areas, and within 6’ of sinks, bathtubs and shower stalls. GFCI protection is also required for certain appliances that have a history of being a shock hazard. Drinking fountains, vending machines, dishwashers and boat hoists are examples of appliances that require GFCI protection.”

Edited to address the right person. Sorry about that.


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## jim18655 (Jan 30, 2018)

NEC is the minimum code and municipalities can go above the minimum requirements. Some cities I've worked in required BX cable when Romex met the code standard for single family homes.  No BX = failed inspection.

Remember, do what you want until there's a problem and the lawyers and insurance companies get involved.

I knew a guy that did maintenance of all types in industrial facilities. He serviced his oil furnace and had a fire that destroyed his house about 6 months later. The insurance and fire marshal determined the fire started in the furnace and held his payment up for over a year. He ended up suing to get his money. They wanted to know if he was "qualified" to work on his own equipment.


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## JPMacG (Jan 30, 2018)

You could put a 1:1 ungrounded isolation transformer between the GFCI and the Teco.   I think that might work, but I may have myself confused.


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## rwm (Jan 30, 2018)

higgite said:


> Mark,
> 
> The quote below is from the NFPA website, authors of the National Electric Code. Most municipalities that I’m aware of (certainly not all) who even have a code, usually rely on the NEC. Like Blacjjackjacques said, you may not be required to have GFCIs for your new circuits. Has the inspector said that you do? If so, have you asked him to point you at the written code or county requirement?
> 
> ...



If you take this regulation literally, it only applies to Receptacles. Hard wiring would be the way to go. Glen-have you confirmed that would be acceptable?
Robert


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## mksj (Jan 30, 2018)

An isolation transformer if floated (neutral and 120VAC) would negate the GFI effect, typically they use a faraday shield to ground to cancel out the EMI/RFI generated. But many 120VAC isolation transformers bond the neutral to the primary  and secondary coils, so I am not sure if this would remedy the GFI tripp situation, vs. 240VAC where both 120VAC legs are floated (isolated). The cost of a 1800 VA isolation transformer like a Tripp-Lite would be more expensive than the VFD, and would most likely need to be modified to float the secondary neutral line. It would seem that it is a very expensive band-aide vs. other options: bypass the GFI at one receptacle, hard wire the grinder to a non-GFI box, buy a 240VAC VFD.


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## tq60 (Jan 30, 2018)

Any type of switching power supply has leakage current due to the magic of how they work so gfi and larger ones do not play together.

Hard wire one option the other is to change outlet to a twist lock type.

Make sure device is properly grounded via the plug and due to the not common interface then likely fine.


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## Dabbler (Jan 30, 2018)

Please let me take a stab at this:  if you use conventional 110V receptacles (15A or 20A) to pass code you have to use GFI, right?

Then how about wiring 4 wire 220V Hubbel plugs as per industrial wiring standards.  you then use the 110V legs to power your machine.  In my jurisdiction, this passes and we don't have to use arc fault.  If *we *do any new wiring *here *for 110V 15/20A plugs, they now have to be arc fault.  All my 220 4 wire twist locks are conforming to the new wiring code.


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## rwm (Jan 31, 2018)

Dabbler said:


> Please let me take a stab at this:  if you use conventional 110V receptacles (15A or 20A) to pass code you have to use GFI, right?
> 
> Then how about wiring 4 wire 220V Hubbel plugs as per industrial wiring standards.  you then use the 110V legs to power your machine.  In my jurisdiction, this passes and we don't have to use arc fault.  If *we *do any new wiring *here *for 110V 15/20A plugs, they now have to be arc fault.  All my 220 4 wire twist locks are conforming to the new wiring code.



That is clever! Just wire the room for 220 but only use half of the receptacle so to speak. I ideally you could balance the loads too.
Robert


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## tq60 (Jan 31, 2018)

Dabbler said:


> Please let me take a stab at this:  if you use conventional 110V receptacles (15A or 20A) to pass code you have to use GFI, right?
> 
> Then how about wiring 4 wire 220V Hubbel plugs as per industrial wiring standards.  you then use the 110V legs to power your machine.  In my jurisdiction, this passes and we don't have to use arc fault.  If *we *do any new wiring *here *for 110V 15/20A plugs, they now have to be arc fault.  All my 220 4 wire twist locks are conforming to the new wiring code.


That is a similar plan but one needs to be certain they do wire with all 4 conductors so the neutral is there and that the breaker is correct size.

Given the op is using a 120 volt input vfd the 240 volt option may not be available.

Another suggestion is to stop by the building department and discuss the options with them as they are local enforcement and may have easier suggestions as the gfi may only be required if within a given distance to outdoors or some other thing and be sure to get a copy of the rule.


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## Blackjackjacques (Jan 31, 2018)

mksj said:


> An isolation transformer if floated (neutral and 120VAC) would negate the GFI effect, typically they use a faraday shield to ground to cancel out the EMI/RFI generated. But many 120VAC isolation transformers bond the neutral to the primary  and secondary coils, so I am not sure if this would remedy the GFI tripp situation, vs. 240VAC where both 120VAC legs are floated (isolated). The cost of a 1800 VA isolation transformer like a Tripp-Lite would be more expensive than the VFD, and would most likely need to be modified to float the secondary neutral line. It would seem that it is a very expensive band-aide vs. other options: bypass the GFI at one receptacle, hard wire the grinder to a non-GFI box, buy a 240VAC VFD.



I agree that the iso transformer would render a downstream GFCI inoperable since there would be no ground reference, but any of the iso xfmr windings would have no connection to either neutral or ground.  You may be thinking of how an autoformer is connected. With an ISO xfmr, you should be able to grab any secondary lead in one hand, and place your hand flat on a solid ground surface and experience no current.


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## Dabbler (Jan 31, 2018)

tq60, with 4-wire plugs, there is both 220V and 110V across the legs.


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## markba633csi (Jan 31, 2018)

Jacque: there is a slight interwinding capacitance however which might produce enough current to deliver a mild shock.
Mark


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## Eddyde (Jan 31, 2018)

Blackjackjacques said:


> With an ISO xfmr, you should be able to grab any secondary lead in one hand, and place your hand flat on a solid ground surface and experience no current.


I seriously doubt that. If electrical potential is present, it will drain to ground. And if anyone wants to test this, please use a meter or tester, not your hands.


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## ch2co (Jan 31, 2018)

I started out with a 4 wire twist lock plug but changed it out to hard wiring from box to the VFD. Licensed electrician friend  approved it all and said the wiring I did was pleasantly overkill for the application. All 110v outlets are GFI protected and have caused no problems with any other shop tools.


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## jim18655 (Jan 31, 2018)

I think there was less discussion at NASA for the first moon landing


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## Blackjackjacques (Jan 31, 2018)

markba633csi said:


> Jacque: there is a slight interwinding capacitance however which might produce enough current to deliver a mild shock.
> Mark



At high impedance, there may be a measurable voltage owed to capacitance, but it should go to flat at low impedance.  ISO transformers are often used to decouple metal hulls and protect against stray current corrosion owed to shore power as well as in patient systems involving electric current as a means of protecting against a ground fault, etc. so any current at practical loads (low resistance) will be zero.  Sure, if you connect a high z meter across a secondary leg and ground, you may read voltage, but the current will be micro amps, and as soon as you place a load across, the voltage will drop to zero.


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## Blackjackjacques (Jan 31, 2018)

Eddyde said:


> I seriously doubt that. If electrical potential is present, it will drain to ground. And if anyone wants to test this, please use a meter or tester, not your hands.


Of course and I would also not test with my hands--I used the "hand" model because the hand surface area against a flat metal surface is what is used by the testing institutions and the electric shock safety standards (IEC 60479-1 in particular) as the basis for such safety.  However, if you have an ISO transformer and measure current from a secondary leg to ground - it will read zero or close to it.


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## 4GSR (Jan 31, 2018)

Okay guys, we all have spoke with our ideas of what to do.

The OP has to follow what the local building inspector say he has to do.  Our say so's don't count.
So let's move on and put this to rest.

Ken


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## coherent (Jan 31, 2018)

May be a silly question but I didn't see if you said or what your motor HP rating is but... Are you running a 15amp or a 20amp breaker/receptacle? Most 110/120v to 3ph VFDs that I have seen call for a 20 amp circuit/receptacle for a 1hp motor. I'm sure a 1hp is pulling close to or more than 15 amps on startup and GFI breakers always seem a little more finicky. So if it's a 15 amp setup that could be the issue.


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## Blackjackjacques (Jan 31, 2018)

My curiosity got the best of me and so I had to update myself on GFCI's and found this excellent IAE article indicating new GFCI classes for industrial applications and higher voltages still providing human shock protection.  The article is well done and is good reading.

https://iaeimagazine.org/magazine/2...have-a-proactive-option-for-shock-protection/


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## markba633csi (Jan 31, 2018)

I had a great old electronics teacher, Mr. Evans, used to stick a paper clip in the outlet and invite us to feel the electricity. 
He said "don't worry you have at least 1 million ohms from your finger to your toes.  He didn't have many takers.  Not even me, and I've had many shocks
Just a wimp I guess LOL


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## Latinrascalrg1 (Jan 31, 2018)

Ok you (OP) stated that you added 3 GFCI outlets, were those 3 outlets each individual home runs back to the breaker box or are they on the same line as a single home run back to the breaker box? Or did you tap into an existing circuit?  If they are on a single line either back to the box or tapped into an existing circuit how did you wire them?  I think I remember either being told or reading the following information so I'm not sure of the validity of this so please read it more as a question to verify verses me stating a fact.......I think i remember that running more then 1 GFCI on a circuit will make them fault out and act crazy. You should only need 1 GFCI outlet that can protect all outlets past the gfci on the same line if you wire it so that you utilize the Line/Load terminals of the gfci correctly! (I would assume this would be dependant on the local codes and what you will be powering?) 

If this is not correct info would you explain what is not correct for me so that I know for future reference please?  Thanks.


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## whitmore (Jan 31, 2018)

Blackjackjacques said:


> I agree that the iso transformer would render a downstream GFCI inoperable since there would be no ground reference...



Happily, that's not the case.   GFCI is the recommended way to make-shock-safe a 
two-wire (neutral and line) receptacle even when there is no ground wire available.   There's little
labels supplied with the GFCI so you can tag those outlets as not-grounding.
So, a short extension cord, with a GFCI on the end, is a worthwhile precaution
if you have two-wire or ungrounded (or just uncertain) power outlets.



Blackjackjacques said:


> With an ISO xfmr, you should be able to grab any secondary lead in one hand, and place your hand flat on a solid ground surface and experience no current.



Not always !!
Isolation transformers are available in TWO different types, either with neutral/ground bonding
on the output side, or with neutral floating on the output side.   If you want shock-safe
due to transformer isolation while working on live circuits, only the neutral-floating
type is going to work for you.    This item TrippLite iso transformer  has a 'N-G' output
limit of 0.5V, indicating that it has the neutral on the output bonded to ground on output (from
the third prong of the input wire).   Hold the output LINE wire, touch a ground, and you get a shock.

It's confusing, and a little scary, that the 'isolation' situation is so poorly described.  I've
tested both types of isolation transformers, they both DO have legitimate uses.  A
three-prong outlet tester will 'fail' the isolation transformer output socket unless there's
a neutral-ground bond.


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## tq60 (Jan 31, 2018)

Dabbler said:


> tq60, with 4-wire plugs, there is both 220V and 110V across the legs.


Only if wired that way...Some are 3 phase...Many 4 wire plugs but which one matters.

Main point is most common of the 4 wire types are the 50 amp range plug used for rv too.

The op may not have 240 vac available so they used the boosting vfd.


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## Blackjackjacques (Jan 31, 2018)

whitmore said:


> Happily, that's not the case.   GFCI is the recommended way to make-shock-safe a
> two-wire (neutral and line) receptacle even when there is no ground wire available.   There's little
> labels supplied with the GFCI so you can tag those outlets as not-grounding.
> So, a short extension cord, with a GFCI on the end, is a worthwhile precaution
> ...



I think the industry has done a decent job in describing iso xfrmr connections and their function.  While jumper configurations permit various needs, the general notions in the contexts of electrical safety, patient safety, stray current corrosion applications for boaters, etc understand the floating nature, benefits and limitations of these devices.   The widespread understanding for ISO transformers is as I identified.  However, in the testing realm, I understand how iso xfmrs may be used and special bonding features, particularly in regard to noise reduction.


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## Dabbler (Feb 1, 2018)

Tq60: The Electrical code clearly describes the wiring for single phase twist lock plugs, which is the general topic here.  Yes 3 phase is a possibility, and I correctly wire the output of my VFD to 4 wire plugs, but it is out of the scope of this thread.  I use 20A twist locks for 50% of my shop connections, and standard 15A 110V duplex for the rest.  In my jurisdiction, *and coming soon to many others* is the requirement for arc fault on all new wall sockets.  Equipment manufacturers will take years to catch up with this electrical code requirement.  My advice is a way for the OP to get his wiring to code, passed, and keep working without deception.  This is important if he wants his insurance to remain intact.

I have no experience with any 50Amp twist lock.


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## tq60 (Feb 1, 2018)

You are correct but missed my point which agrees with your general statement...

Over the years we have seen and read of many odd ways of folks performing wiring that does not meet code then ask and defend the bad ways.

The mention of "4 wire plug" could mean anything without the code number, we use the numbers when needed for documentation but they are not etched in memory as other things are so not stating them here.

We have many 240 volt plugs in the shop that are the old dryer type that likely do not meet current code but considering neutral not needed they meet the function of L1, L2 and safety ground.

Knowing every township can have their own modified version of code for almost everything we usually suggest one possibility of a solution so the op can research it to understand it along with suggesting they follow up with local building department to develop plan that meets the local code.


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## JPMacG (Feb 1, 2018)

This has been an interesting and educational discussion.  I am an electrical engineer (microwave antennas) but have no background in power and am sadly lacking in this area.   Thanks everyone!


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## tq60 (Feb 1, 2018)

JPMacG said:


> This has been an interesting and educational discussion.  I am an electrical engineer (microwave antennas) but have no background in power and am sadly lacking in this area.   Thanks everyone!


Lots of differences between them!

Close to 40 years in radio including tractors to cell switches with a bit of microwave in the middle.

One of the least understood things due to lack of front end engineering...

Good luck!


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## Glenn Brooks (Feb 1, 2018)

To answer a couple of questions. It’s a 15 amp circuit, and all three electrical fixtures are in line.  In addition, another GFCI fixture is in line on the circuit betweeen the triplex box and the main.  The grinder is a common 8” 3/4 hp Baldor pedestal model, in good condition. It runs perfectly well on the original legacy circuit, with the VFD installed and grounded to the frame and motor. Also the County requires GFCI on nearly all grade, or below grade locations, regardless of proximity to wet spaces. 

To confirm, I called the King County electrical inspector and was informed basically, all newly installed fixtures need to be GFCI.   This of course is a vastly expanded and altered definition of what the NEC actually requires. The inspector also stated GFCI works properly with all electrical equipment and detects ground faults, shorts, in electrical motors thus MY grinder must be defective, likely with an inadequate ground. Of course this is also uninformed nonsense, as VFD’s are widely known to NOT function with GFCI’s, hence the problem of tripping the circuit when NO SHORT HAZZARD EXISTS. mine certainly trips the GFCI as soon as it is turned on, and at no time with non GFCI circuits. But who am I to argue with such a knowledgeable guy.


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## Bob S. (Feb 1, 2018)

Glenn Brooks said:


> To answer a couple of questions. It’s a 15 amp circuit, and all three electrical fixtures are in line.  In addition, another GFCI fixture is in line on the circuit betweeen the triplex box and the main.  The grinder is a common 8” 3/4 hp Baldor pedestal model, in good condition. It runs perfectly well on the original legacy circuit, with the VFD installed and grounded to the frame and motor. Also the County requires GFCI on nearly all grade, or below grade locations, regardless of proximity to wet spaces.
> 
> To confirm, I called the King County electrical inspector and was informed basically, all newly installed fixtures need to be GFCI.   This of course is a vastly expanded and altered definition of what the NEC actually requires. The inspector also stated GFCI works properly with all electrical equipment and detects ground faults, shorts, in electrical motors thus MY grinder must be defective, likely with an inadequate ground. Of course this is also uninformed nonsense, as VFD’s are widely known to NOT function with GFCI’s, hence the problem of tripping the circuit when NO SHORT HAZZARD EXISTS. mine certainly trips the GFCI as soon as it is turned on, and at no time with non GFCI circuits. But who am I to argue with such a knowledgeable guy.



Glenn I have the same VFD  as you  plugged into a GFI protected outlet it runs my old Delta drill press and works without tripping. Am I just lucky?


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## whitmore (Feb 1, 2018)

Bob S. said:


> Glenn I have the same VFD  as you  plugged into a GFI protected outlet it runs my old Delta drill press and works without tripping. Am I just lucky?



The GFI is probably sensing a 'fault current' because of the RF filtering in the VFD, but the GFI trip point
is set at (5 mA?) and it is common practice to steal a little current (like, one-third of the trip current)
in some appliances.   For RF filtering purposes, a small capacitor on the line/ground will take
acceptable 60 Hz current, below the GFI trip point, BUT will also pass some switching current
at high frequency.   Other appliances ditto pass small currents.

So, the VFD, and the load on the VFD, and the filter detailed characteristics, and the capacitance from line
to ground of everything ELSE on the circuit, and the high frequency sensitivity of the particular GFI module,
all combine to determine whether it trips.    The production year/month of a VFD might
determine whether the RF filters put 1.5 mA to ground, or 3.5 mA.   Perfectly good devices, 
no shock or fire safety problems at all, can be  incompatible with the GFI.   

This suggests that a breaker-box GFI (one unit protecting a half dozen outlets) is more likely
to trip than an end-node GFI (one unit protecting two outlets).   It also suggests that a single
component (the powerline filter) of the VFD can be the only problem, and those can be replaced
fairly easily.    Me, i'd see if it was possible to clamp a ferrite common mode choke on the
line/neutral wires inside the VFD.   Or, ask the manufacturer of the VFD.


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## Dabbler (Feb 1, 2018)

Glen, without taking a meter an scope out to your garage, I can't offer much more.  I'm an engineer, but I consult with an RF engineer when I have weird problems...  You might consider asking for a little advice from an EE to help you out with the inspector, however it seems the only solution that will satisfy the inspector is wire a completely different circuit.


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## mksj (Feb 1, 2018)

There is no EMI/RFI filtering on the Teco VFD unless you add one.  There is extensive information as too the leakage issue with VFDs, some manufactures have taken extensive and costly measures to minimize this and electrical noise radiation, but not at this level. The design of the line filter has an effect on the GFCI trip characteristics, the ones I typically use for electrical noise attenuation will outright trip them because of a high (intentional) leakage current to ground. I have used the TDK/LAMBDA-MC1230 noise filters on some VFD systems, they are rated at less than 1 mA of leakage current. Worth a try, connect it close to the VFD.
https://www.ebay.com/itm/LAMBDA-MC1230-Surplus-New-In-factory-packaging/391809295708

Sometimes there can be slight variations between GFCI's as to tripping, but they all most meet the same trip criteria for a Class A ground fault. I have worked with a number of individuals who have used the same Teco and all had the same issue with the GFCI tripping (these were the 120V version). There may be some variations from VFD model to model brand to brand, but this is a "known" problem with VFDs with no quick or "cheap" fix other than to wire a socket without a GFCI. You will have one GFCI feeding a branch of downstream sockets, you can move the GFCI to the next socket down and use the first as a non-GFCI and if you need to meet code, hard wire it. QED.

ABB Reference document. These have already been stated.
LINE SUPPLY GFCI CIRCUIT BREAKER’S AND AC DRIVES

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.

Documents or other reference material: None

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.


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## 4GSR (Feb 1, 2018)

Glen,

Did you by chance ask the inspector about needing the circuit for running a VFD from?  He might change his tune and offer a recommendation. 

Worse yet, blow his mind up trying to figure out why you have a VFD in a residential setting.


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## Blackjackjacques (Feb 2, 2018)

whitmore said:


> The GFI is probably sensing a 'fault current' because of the RF filtering in the VFD, but the GFI trip point
> is set at (5 mA?) and it is common practice to steal a little current (like, one-third of the trip current)
> in some appliances.   For RF filtering purposes, a small capacitor on the line/ground will take
> acceptable 60 Hz current, below the GFI trip point, BUT will also pass some switching current
> ...





whitmore said:


> GFI is probably sensing a 'fault current' because of the RF filtering
> in the VFD, but the GFI trip pointis set at (5 mA?)
> .



You mean leakage current and not fault current - don't you?  You can feed a line to neutral fault current through a GFCI device all day
until the branch OCP device trips.  Also, there is no "set" point for GFCI tripping.  GFCI devices follow an inverse time-current curve described by the equation T=(20/I)^1.43, where T is time in seconds, and I is current in mA.   So at 5 mA, the GFCI could take over 7.2 seconds to trip, while 20 milliseconds @ 300 mA current.   This curve is based on the IEC 60479 time-current exposure curves.





whitmore said:


> , the VFD, and the load on the VFD, and the filter detailed characteristics, and the capacitance from line to ground of everything ELSE on the circuit, and the high frequency sensitivity of the particular GFI module,
> all combine to determine whether it trips. The production year/month of a VFD might
> determine whether the RF filters put 1.5 mA to ground, or 3.5 mA.



GFCI devices do not trip at 3.5 mA and below - or at least they are not supposed to and cause for rejection under the UL 943. 




whitmore said:


> suggests that a breaker-box GFI (one unit protecting a half dozen outlets) is more likely
> to trip than an end-node GFI (one unit protecting two outlets).


Not true - the breaker style GFCI devices are built to the exact same UL 943 standard as are the receptacle devices, as are the temporary power tap GFCI devices.




whitmore said:


> It also suggests that a single component (the powerline filter) of the VFD can be the only problem, and those can be replaced fairly easily. Me, i'd see if it was possible to clamp a ferrite common mode choke on the
> line/neutral wires inside the VFD. Or, ask the manufacturer of the VFD.



I don't know how anyone be so certain that the VFD "can be only problem"  especially based on the information given here, and I also do not believe they can be "replaced fairly easily"  As mksj posted, there is no RF bypassing on these devices unless installed after manufacture, so I don't see where clamping a ferrite choke would do any good.     With the GFCI a mandatory code compliance requirement, and with the given VFD and load device, the only real code-compliant option the OP has is to employ an isolation transformer.


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## whitmore (Feb 2, 2018)

[about a VFD which might draw 3.5 mA current to ground through an RF filter, and RF filter 
    standards changing over time]



Blackjackjacques said:


> GFCI devices do not trip at 3.5 mA and below - or at least they are not supposed to and cause for rejection under the UL 943.



But the VFD isn't the only item on the circuit, and it's the sum of that and other items (like, the motor that
the VFD drives,  worklights, lube pumps,
cellphone chargers and the like) that matters.   Six-outlet branch circuits with one GFCI might
trip when the VFD is plugged in, even if the VFD alone is not a problem.



> As mksj posted, there is no RF bypassing on these devices unless installed after manufacture



In my years of poking into powered apparatus, I've never seen a switchmode power supply, as a VFD
certainly is, that did not have a number of RF filter elements on its AC inlet.   Maybe there's
not a label that proclaims RF filter, but it's there.


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## Dabbler (Feb 2, 2018)

so...  without wanting to offend, and recognizing a diversity of views here, I consulted with an active electrical engineer who specializes in custom RF and power circuits.  I'm not trying to pull a 'Authority trump card here', but to provide some additional info for consideration...

If putting simple EMF filters doesn't fix the problem, then there must be either leackage or common mode current exceeding the trip threshold.  This is an extremely dangerous situation, despite the fact you have been runing the VFD for years.  Repair/replacement is the safest approach. Any new modern VFD should be designed with AFCI and GFI in mind even the commercial units.  I was working in a commercial shop a few years ago where all the machines were on $$$ GFI circuits.


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## ch2co (Feb 2, 2018)

My (10+year old) Hitachi VFD came with a rather thick and highly detailed manual that has a chapter about how VFDs can put a lot of high frequency trash into the incoming power line. They provided chokes (inductors) that can be placed in the 3 wire VFD input power line to protect other components on the same line from all this “hash”. Your GFI would be one of these sensitive components.  I’ve not run into any problems with me system without such protection, however my VFD is hardwired to the mains line without a GFI. None of my other GFI’s in my shop have given me any troubles, but they are on another set of circuit breakers in my mains panel. 





with a


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## rwm (Feb 2, 2018)

I'm changing over to steam....
R


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## Blackjackjacques (Feb 2, 2018)

Dabbler said:


> so...  without wanting to offend, and recognizing a diversity of views here, I consulted with an active electrical engineer who specializes in custom RF and power circuits.  I'm not trying to pull a 'Authority trump card here', but to provide some additional info for consideration...
> 
> If putting simple EMF filters doesn't fix the problem, then there must be either leackage or common mode current exceeding the trip threshold.  This is an extremely dangerous situation, despite the fact you have been runing the VFD for years.  Repair/replacement is the safest approach. Any new modern VFD should be designed with AFCI and GFI in mind even the commercial units.  I was working in a commercial shop a few years ago where all the machines were on $$$ GFI circuits.



I would not be offended, and I am an active and licensed electrical engineer specializing in power and control as well as having served on the UL 913 STP for 15+ years now.  Inasmuch as I came here to learn to machine stuff, I am instead loitering in the electrical forum rather than use my brand new Rong Fu 45, that still needs for me to install a DRO still in boxes underfeet.  I'll rely on the old adage "if all you have is a hammer, everything looks like a nail.   However, I have made progress and last night did put together the MachTach RPM kit. 

Getting a 2nd or 3rd opinion is good. 

Although the leakage is sufficient to trip a GFCI when using a VFD appliance, there is no danger or risk whatsoever.  UL will be the first one to tell you that GFCIs should not be used with such equipment, especially commercial equipment exactly because of the very condition described.  In fact, UL will even tell you that many residential equipment, including PCs, printers, etc, may trip a GFCI.  If a ground fault system is required, they will point you to the other GFCI classes.   I have many pieces of equipment that I cannot use on a GFCI protected branch circuit, including UPS, printers, PCs which I just assign to a non-GFCI circuit.  That is code compliant here in my county.  For circuits with GFCI protection that I must share with equipment that cannot run off a GFCI, I use isolation transformers to feed a common receptacle bank. I have to do this with a bank of vacuum tube test equipment.  I also have a pair of old tube Mac 30 amplifiers that I also feed through an ISO transformer.   There is no way that electric equipment manufacturers, especially workshop or commercial equipment vendors will make use on an GFCI (or AFCI) a priority performance condition.  In this particular case, I would try to persuade the code official, appeal the lower level decision and ask for a written decision and submit to the appeal board, a written explanation of the problem, as well as include whatever documents (including manufacturer's statements) detailing the conflict.  I can't imagine any code authority denying such an application for waiver, especially given what appears to be a draconian interpretation of whatever NEC edition they are invoking.  If this fails, then the ISO Xfrmr is the next best solution while maintaining code compliance.


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## whitmore (Feb 2, 2018)

Dabbler said:


> If putting simple EMF filters doesn't fix the problem, then there must be either leackage or common mode current exceeding the trip threshold.  This is an extremely dangerous situation...



Good, yes, it's about current exceeding the trip threshold.   But, one style of filter puts a capacitor-to-ground
in the circuit, and that capacitor (sometimes called an X capacitor, there's safety requirements for 'em)
might be the only 'leakage' current path.  That leakage path is just like the GFCI "test" button,  NOT
a shock hazard, but the GFCI doesn't know that.   Not 'extremely dangerous', but not
useful either, because the filter, or the test button, shuts the GFCI down.

For (a previous employer's) medical equipment, we had a budget of how many such acceptable 
capacitors could be used in a complex system, and it was 2.   No shock hazard, but simply plugging three 
acceptable and safe devices into a branch circuit could fail safety tests, or trip a GFCI.

The kind of filter one wants to use in a VFD is one that does NOT have an X capacitor, because
the high frequencies a VFD generates can put more current through an X capacitor.


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## markba633csi (Feb 3, 2018)

Pain in the %SS .  Look at many 220 volt clothes dryer installations.  Two hots and a neutral, no ground there. Well what happens if the neutral floats?
You guessed it- shock hazard.  Same thing with many welder installs.
Give me a good old ground wire any day, instead of relying on some fancy-shmancy electronics to save me.  Fooey!  OK rant over. 
Mark S.
Authorities are probably reading this: Look! a malingerer, a malcontent- arrest him!


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## Splat (Feb 12, 2018)

I've been told not use to VFD's with GFCI's. The one time I tried it, before I knew better, it tripped the GFCI. That's when I started asking around and was told to not do it.


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