# circuit breakers before a VFD



## vedoula (May 16, 2011)

Not sure if this is the correct home for this post... 

I am setting up a variable frequency drive, VFD, to drive a 3-phase motor of a new old lathe. I would like to put a circuit breaker before the VFD. The input is single phase - there is a single hot wire, a neutral, and the ground. 

Normally I would pass the hot wire through a single pole circuit breaker. But I worry that different outlets may interchange the hot wire on the right vs left (it was so in my previous home). So I would like to assume that I will not know which line is the hot and which is the neutral when I plug the lathe in an outlet.

I'm thinking of using a 2-pole circuit breaker. Pass the hot wire and the neutral from each pole. Irrespective of where the hot is in the plug (right or left) I'll be covered. 

Is this correct? Please suggest pointers.


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## JorgensenSteam (May 16, 2011)

They sell inexpensive outlet testers.
You should purchase one and verify that the hot-neutral-ground connections for the outlet are correct.

You should not use a 2-pole circuit breaker for a 120 volt, 1-phase outlet as this is illegal in the US NEC (National Electric Code), and also unnecessary.

Size your input circuit breaker and wire in accordance with the instructions furnished with the VFD, and do the same with the load size wiring to the motor (per the manufacturer's instructions).

Newer homes are generally have their 120 volt outlets wired correctly, but the older homes tend to have wiring which is too small, and wiring with rotten insulation and poor connections. If you don't have relatively new wiring, you should consider having a new dedicated 120 volt outlet with the appropriate sized wire and breaker installed by a qualified person.


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## vedoula (May 16, 2011)

thanks, I'll follow this suggestion.


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## Admiral_dk (May 17, 2011)

> You should not use a 2-pole circuit breaker for a 120 volt, 1-phase outlet as this is illegal in the US NEC (National Electric Code), and also unnecessary.



"Funny" that not using a two pole circuit breaker is illegal in most of the rest of the world ...  :

We simply do not think that the US way is safe enough .... Our fire insurance is not valid if we have any equipment wired the US way in our houses !!!!


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## bezalel2000 (May 17, 2011)

Hi Vedoula 

If it's electrical safety your looking for it may be worth the little extra cost to install a two pole RCD (Residual Current Device) or ELCB (Earth Leakage Circuit Breaker) these devices effectively detect any current difference between Hot and neutral and trip if its more than about 30mA. (if there different, the current is going somewhere you don't want it to)
 That's good insurance for the heart beat, which I'm told can stop when hit with around 40mA at 50 or 60 Hz

Bez


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## JorgensenSteam (May 17, 2011)

Wiring methods vary depending on where you are in the world.

The only arrangement that requires the neutral to be opened in the US (that I am aware of) is for a fuel dispensing system.

Since the neutral in the US residences (when wired correctly) is connected to the ground conductor at the service entrance panel, nothing is gained by opening a conductor that is already at ground potential.
If the practice of opening the hot conductor only were dangerous, then hunderds of millions of circuits in the US would be experiencing problems, but they are not, so experience and theory showns this method is safe.

The item that is critical to have for safety is a good ground wire run from the panelboard to the receptacle. A properly grounded receptacle will allow the circuit breaker to trip if the load develops a fault, such as a shorted winding in a motor.

People create havoc when they start modifying their home wiring and do not do so correctly, such as reversing the hot and neutral, or reversing the neutral and ground conductors. The neutral conductor carries full current all the time; the ground conductor carries current only in a fault condition, and they are not interchangeable even though they are both at ground potential, since reversing them will cause full current to flow through the metal electrical housings and anything that touches the housings.

The neutral conductors of old US appliances use to be connected to the metal frame of the equipment, thus the danger of reversing the hot and neutral.

GFCI (ground fault circuit interrupter) receptacles are a good idea in the shop, and I highly recommend them, since they compare the current flowing out the hot conductor with the current returning on the neutral conductor, and open the circuit if the two do not match (if the two do not match, it means a stray current if flowing, possibily through a human). GFCI receptacles in the US are sold in 15 ampere and 20 ampere, at 120 volts, and a large VFD will draw more current than either of these devices will handle. The circuit breaker, receptacle and wire should be sized for at least 125% of the line side full load current of the VFD.

There is also the arc fault receptacle used in the US, and this device is designed to open under a low current arcing fault. An arc fault circuit breaker may see the line side of a noisy VFD as an arc fault. A properly sized GFCI receptacle feeding the load would be a much better application of a safety device.

The GFCI breakers I have used have been unreliable, and fail frequently, so I use a 20 ampre GFCI receptacle, and install it at the beginning of the circuit so that it protects all downstream receptacles. If you wire a GFCI receptacle wrong, it does not give GFCI protection either for itself or for the downstream receptacles, and they make testers which inject 10 mA of stray current to test GFCI receptacles. Pushing the "TEST" button on a GFCI receptacle does not test it for incorrect wiring connections, but only tests the internal components of the GFCI receptalce, so don't be fooled by pushing the "TEST" button.

Again the best and first line of protection is a good ground wire and good ground connections.


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## kvom (May 17, 2011)

> The GFCI breakers I have used have been unreliable, and fail frequently, so I use a 20 ampre GFCI receptacle, and install it at the beginning of the circuit so that it protects all downstream receptacles.



That's how all the 120V circuits in my shop are wired. Cheap insurance.


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## JorgensenSteam (May 17, 2011)

Admiral makes a good point, and one that some may not be aware of, but much of the typical residential wiring in Europe (as I understand it, correct me if I am wrong) is 220 volt, 1-phase, wired like the US 240 volt, 1-phase.

Both would use a 2-pole breaker, and both should use a 2-pole breaker only, even though a 1-pole breaker is occasionally mentioned for a 240 volt circuit.
Using a 1-pole breaker for a 240 volt circuit is dangerous, since a fault will only trip the one pole, leaving the other leg energized and without overcurrent protection.

The use of 220 volts for standard home receptacles is a good idea since you get twice the load capacity for a give wire and breaker size. I am not sure why this never caught on in the US. For a 240 volt single-phase circuit, a line-to-ground fault is only 120 volts, which is the same as a 120 volt circuit. Most electrical faults are line-to-ground.
Using 220 volt circuits for all loads does double the space requirements for the panelboards, since most of your circuit breakers in a European panelboard would take up two poles at 220 volts, instead of just one pole at 120 volts.

One big problem in the US is the use of 1,500 watt, 120 volt portable heaters.
The cords for these heaters are sized correctly, but when plugged into a worn receptacle with a lose connection, they quickly overheat the receptacle, plug and cord, and cause fires.

Another big problem in the US is that you can buy a 12 gauge, 14, 16 and sometimes 18 gauge extension cord. Too often, people purchase cords with regards to cost, when they should be looking at circuit ampacity. Often times, large 120 volt loads need a 12 gauge wire or larger, but I often see these loads fed with a 16 gauge cord, and the cord and plug are running very hot, which means a fire is imminent.


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## lordedmond (May 18, 2011)

BigOnSteam


in the US the 240vac is across phases deter tapped to earth , thats were they get the 110 phase to earth for normal domestic use

As I under stand for the 240vac US system you would need a linked two pole MCB to isolate the circuit because of the two live to earth wires

In the UK the 220vac is one phase and the neutral is at earth potential therefor our line is at 220 above earth

In the UK a single pole MCB will be Ok as its in the live wire , using two ( unless they are linked ) you could have the neutral one tripped and the live one still on circuit is then still live 

Stuart


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## Admiral_dk (May 18, 2011)

OK, let's start with at small correction. In Europe, before the European Union started to take interest in those matters, we had countries that had 220V and others that had 240V. This wasn't practical, when the union wants easy trade across the borders, so from 1997 (as far as memory serves) it has been 230V in all of Europe. You can still find quite a bit of old installations with only Live and Neutral wires, but all new installation must be three wires ; Live, Neutral and Earth .... AND Earth must under NO circumstances be connected to Neutral. This is simply as an extra protection, in case the Neutral wire isn't at zero volts - this can happen as a result of a thunderstorm or a major accident in a power panel between the transformer (they aren't local like in the US, but covers a certain area) and the end user - in those cases, you got an extra protection from an Earth wire that still is at zero volts and connected to the chassis of your equipment - the equipment might not survive, but you do !!!!

Our DPDT circuit breakers MUST be true DPDT (Double Pole, Double Throw) in order to prevent that we only disconnect the Neutral wire.

And I do know how big a problem it can be. One of my friends back when we where young was called out to an old farmhouse and told to bring the electric installation in working order. So he started at the power panel (where the power enters the building) and removed ALL fuses, so he was sure that no one could plug them back in while he where working. He the went into the kitchen and climbed a ladder up to the only lamp socket in the ceiling, started to disassemble it and got a rather bad electric shock - result ; he fell down to the floor, but was other wise unharmed, except for some bruises. Thank god we still used wooden ladders back then. This resulted in an investigation - result ; the installation was from the very earliest time in domestic electricity, where we had DC instead of AC power. When it was converted to AC, no one cared to check where the fuses where in the installation and it turned out, the they where in the Neutral wire instead of the Live wire. This meant that the Power Company had to shut down the area, so this single house could have the wires in the power panel switched to the correct way !!!!


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## lordedmond (May 18, 2011)

A correction 

In the UK the neutral is connected to the earth it is done in many places in the distribution network

point 1 the neutral is bonded to earth at the transformer ( power company )
point' many all new installations ( a good number of years ago ) have a PME system and are fed to the domestic premises by a TWO core cable L and N ( more like a big coax ) it its the householders responsibility to provide a good earth point ( earth rod ) and then the neutral is bonded to that earth at the cutout before the meter

this is to prevent the neutral volt raising due to the imbalance in the network ( the power is distributed as three phase and neutral ) , theres at each premiss the neutral is at or very near the earth potential

note I am talking about the UK in this instance

you are correct in saying that the installation is 3 wire LN&E but the supply is L & N


Stuart


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## Admiral_dk (May 18, 2011)

I stand corrected - and you're right, here in Denmark too - although we aren't supplied with two but four wires.

The Power Company supplies three phases of Live and Neutral (L1, L2 & L3 + N) - we MUST provide an Earth rod with a maximum resistance of ??? (I'm not sure, but I do know that it depends on the size of the installation - so many private homes are well served with a 2-4 meter rod and many industrial plants can have up to or more than a 100 meter rod).

The voltage between any two of the three phases are 400 volts and the voltage between any of the phases and Neutral are 230 volts.

The Law also requires that the first connection on the power panel is a HPFI (Hypersensitive, Pulse, Fault, I=current) relay, what you call a RCCB in England and that the fuses are next, followed by the circuit breakers. Now the last two are normally one unit and we have them in two flavors ; one that breaks L and N for simple one phase parts of the installation (E.I. lamps) and one that breaks L1, L2, L3 & N for the three phase units in the installation.


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## lordedmond (May 18, 2011)

Ok 

My pet moan on forums is when Electrical questions come up relating to the mains , not the internal wiring of a machine, is that people do not make it clear which country they are from your comments bring that to light in the UK thing are different to Europe and the USA

I am very familiar with the UK system ( being an electrical engineer ( power ) for 37 years until I gave up work 15 years ago, I do know how the USA system works for supply , but alas they way things are done in Europe differs enough to cause a discussion point 


Stuart


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## mu38&Bg# (May 18, 2011)

Learned something here. I want to add a sink for washing up in the shop, but it's going to end up being too close to a 220 outlet for comfort. I found that GFCI breakers exist for 220V and will be getting one prior to the sink installation.


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## JorgensenSteam (May 18, 2011)

Wow, there is a lot more variation in Europe than I imagined.

Luckily, there is some consistency across the US, especially in residential wiring.

Most US residences are fed from single phase transformers, with a 240 volt secondary coil and a center tap. Line-to-line is 240 volts, and either line to the centertap (neutral) is 120 volts. The centertap of the transformer is grounded at the transformer, and another ground rod is installed where the electricity enters the house.
The two lines and the neutral are brought into the home (3-wires), and the ground and neutral busses are bonded at one point only, which is in the service entrance panelboard. The neutral and ground wires are always completely isolated from each other except at the since bonding point in the service entrance panel, since it would be dangerous to do otherwise.

We don't do relays in residential work, but use electromagnetic breakers or fuses only. Generally fuses are only seen in the older homes.
The problem with fuses is that you can blow only one of two fuses that feed a 240 volt load, whereas a two-pole breaker will open both lines.

Land in the US is so far flung and rural that we generate at 3-phase, but split the circuits for residential/rural areas with small loads, so that only one phase feeds a given area. That allows the power company to bring only one phase wire through an area.
Three phase distribution is generally via a grounded "Y" system, and the neutral is brought along the pole below the crossarm for the three phases. The neutral is grounded at every third pole or so (multi-grounded neutral) to help stabilize the phase voltages.

Our thermomagnetic breakers have two elements. One element is the instantaneous function coil, which trips on sudden and large faults, and the other is an overload element, which is a bimetalic thermal element which trips the breaker on long-time overloads that may be just over the rated current of the breaker, and which would not otherwise trip the instantaneous element.

Industrial breakers are generally thermalmag for the smaller sizes, and electronic for the larger sizes, with ground fault required for breakers 1,200 ampere and larger on Y systems. Industrial breakers generally have dials to adjust the settings for long-time, short-time, instantaneuous, and ground fault.

The only place we use DPDT (other than as a relay in control systems) is for transfer switches for switching loads to generator sets.
I have not seen a DPDT breaker used in the US, and I am not sure why you would use this to feed a load under normal conditions.

Most appliances in the US are either 120 volts, which use Line-Neutral-Ground, or 240 volts, which use Line1-Line2-Ground.
240 volts referred to in residential work is generally assumed to be 240 volts, 1-phase.

Appliances line clothes dryers use 240 volts and 120 volts, and a feeder to this appliance is L1, L2, N, G, which allows the heating element to run off 240 volts, and the motor to run off of 120 volts. The motor is generally has separate overcurrent protection or overload protection in the dryer since the breaker feeding a dryer is generally 30 amperes, 2-pole, which is too large to protect the motor.

The home machinist folks in the US have to purchase phase converters to get 3-phase in the home, since the power companies generally do not provide 3-phase for residential services.

Transfer switches used with generator sets are generally two switches built into a common cabinet and tied mechanically, to allow the load to be transferred between one of two sources. Transfer switches are normally break-before-make to avoid paralleling the genset with the utility company power.

Large industrial installations sometimes use break-before-make transfer switches if they want an uninterrupted load transfer, and can afford the additional paralleling relay system for synchronization with the power company. You also need permission from the power company with this arrangement.

Most residential panelboards are in the 200 ampere size, and the better panels have a 2-pole, 200 ampere main circuit breaker (thermal-mag).
Breakers feeding 240 volt loads are suppost to have their handles tied (from the factory), and the inductrial breakers have internal ties for multi-pole breakers.
Using two separate single-pole breakers to feed a 240 volt load is a bad idea since one may trip while leaving the other energized. Our residential panelboards have staggered bussing in them to give 240 volts between any two adjacent poles, otherwise the 2-pole breaker would not give 240 volts.

GFCI is being used more and more in residential work, since it limits stray fault currents to below 10 mA (the level at which the heart is affected).
Arc-fault breakers are also now being required in some areas of residences, but I do not believe these types of breakers are ready for main stream application, and can give false trips to any load that generates noise such as electronic lighting ballasts, VFD's, computer power supplies, noisy motors, etc. (noisy being electrical noise, not acoustical).

In the industrial world in the US, generally the 408Y/277 volt and 208Y/120 volt systems are used in new installations, with a dry-type transformer used to derive the 208 from the 480.


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## MachineTom (May 18, 2011)

Vendula, Are you in the USA or other places. I ask as if US, there are 120 to 230V 3 phase VFD's but I hear they are pricey. Most VFD's are 230V input, single phase or 3 phase.


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## ttrikalin (May 18, 2011)

machine tom,

i got a VFD 115 to 230 (1Hp) for $106 from www.dealerselectric.com 
just a satisfied customer. 

tom in MA, US


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## JorgensenSteam (May 18, 2011)

You may come out better using a 230 volt, 1-phase input, 230 volt, 3-phase output for motors that are larger than 1/4 hp or so.

Using 120 volts to power the larger motors such as 1.0, 1.5, 2.0 hp is asking alot of a 120 volt circuit.


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## bezalel2000 (May 19, 2011)

What an interesting thread out of such an apparently simple question.

and thanks for your insight B.O.S I found it very interesting



> Land in the US is so far flung and rural that we generate at 3-phase, but split the circuits for residential/rural areas with small loads, so that only one phase feeds a given area. That allows the power company to bring only one phase wire through an area.



Here in OZ we have the similar distance issues but the three phase delta fed (3 wire) at high tension 22 or 33 KV is delivered right into the local street, in the suburbs anyway. There it is transformed to 4 wire 3 phase 415 phase to phase 240 L - N. These 4 wires go past every property. Any property that needs it (and is prepared to pay for it) should be able to tap off 4 wire three phase. all the other houses just get a random phase plus neutral.

Out back its a bit different a single conductor at 11KV and a good earth stake at the end of line. (11KV SWER line) make your own neutral at the earth stake of the 11kv to 240v transformer.  Maybe that's the same as the "one phase wire" your talking about.  



> GFCI is being used more and more in residential work, since it limits stray fault currents to below 10 mA (the level at which the heart is affected).



Pardon the dig here - ;D but the 10mA thresh hold in the US must be related to the percentage of fried Chicken in the body of the population. Since the international standards on safety devices for current protection (IEC 61008 and IEC61009) both rate the safety level at 30mA. 
Maybe foreigners are just a bit tougher or more expendable or something. 
There is also a time factor to be considered too, but lets keep it simple.

I wonder if the world will ever be standardised on this stuff?


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## JorgensenSteam (May 19, 2011)

We were luck here in the US because in the 1930's they created the REA (rural electrification administration), and they drew up standard details for overhead medium voltage power distribution, and those standards were used pretty much everywhere in the US.

Typical transmission circuits are 161 KV, and distribution in this city is both 23 KV for the larger industrial, and 12 KV for the residential overhead primary lines.
A single phase overhead line may also be in the 7KV range.

Many delta transformers were used in the past, and many are still seen today, however, the power companies are phasing those out and going to all grounded-Y transformers, since a grounded-Y transformer winding only has to be insulated for line-to-ground, not line-to-line like a delta transformer, and the grounded-Y transformer gives a solid ground connection without having to have a grounded phase conductor such as with the corner grounded delta transformer.

Corner grounded transformers are a hazard since an unknowing electrician measures zero volts to the grounded phase, and assumes it is not engergized.

Typically, 161 KV feeds into an outdoor utility substation, which has one or more large step down transformers, and several banks of 15 or 23 KV circuit breakers.

Steel plants in this area bring in two 161 KV circuits, and distribute at 35 KV.
One steel plant I worked on had some ridiculous load like 200 MVA, since it had electric furnaces.
They had a huge bank of capacitors and inductors to correct the power factor, since the arc furnaces had a very low pf.

Generally, residential medium voltage circuits have been overhead on wood poles, with oil-filled single-phase transformers mounted on the pole and feeding two or three houses. The new trend is to use all underground medium voltage distribution in the new neighborhoods, and the utility company insists on putting the very ugly green pad-mounted oil-filled transformers on the ground between every two or three houses just a few feet from the street, and very visible. The underground medium voltage cables are constantly ruined by animals that dig underground, and it is common to see entire streets dug up repairing failed cables.

The overhead medium voltage circuits are generally loop fed, with reclosers at the main substation, and switches in strategic locations around the loop.
The recloser will take care of things like tree branches that fall on the lines and then burn or fall clear. The biggest danger to the wood power poles around here are woodpeckers, and automobiles. Some areas resort to wrapping the poles with wire mesh to keep the woodpeckers away. Large birds also cause a lot of problems since they nest on top of the poles, and insulators are now being added to the tops of transformers and some poles to mitigate this problem.

Squirrels are bad about chewing, and one built a nest recently on top of the transformer serving my house, and he chewed right through the 240 volt copper cable next to the transformer, and without any damage to the lucky squirrel.

Due to the large open spaces in the US, you may have one house by itself 20 miles down a dirt road, and that house will be fed from a single-phase overhead line.
Local coops were formed in rural areas years ago, and they are member-owned and operated. We had some serious scandals not too long ago when the politicians decided that deregulating the power companies was a good idea. It was not a good idea, it was a greed-fest in the largest sense.

I guess I have wandered way off thread, but that is the skinny on power distribution in the US.
It is best not to get me started on power distribution, since I rattle on forever.


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## newbiejason (Jun 17, 2011)

dieselpilot  said:
			
		

> Learned something here. I want to add a sink for washing up in the shop, but it's going to end up being too close to a 220 outlet for comfort. I found that GFCI breakers exist for 220V and will be getting one prior to the sink installation.



Here in Australia there is still a minimum distance that an outlet can be away from a sink (500mm left or right)

Running your machine through an ELCB (earth leakage circuit breaker) can cause nuisance tripping as earth leaking from an electric motor is allowable down to 20k ohms, as do hot water services and electric cooktops.


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## bezalel2000 (Jun 17, 2011)

newbiejason  said:
			
		

> Running your machine through an ELCB (earth leakage circuit breaker) can cause nuisance tripping as earth leaking from an electric motor is allowable down to 20k ohms, as do hot water services and electric cooktops.



Hi Jason

That's one of the reasons 10 mA ELCBs are not popular on Aus 

at 240V a resistive load of 20K draws 12 mA where as at 100V its only 5 mA well under the 10 mA trip level that appears to be preferred in the US.

So if you have a 10 mA ELCB tripping on a 240V motor then it could be operating normally. since anything less than 24K would trip it. 

If your ELCB is 30 mA and it's tripping regularly then your Earth leakage is at or below 8K, IMHO that qualifies as a fault.  

Cheers
Bez


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## shred (Jun 18, 2011)

FWIW, my Teco FM50 VFD pops my GFCI outlet every time I turn it on. I did some investigating and ended up with "they do that". I'm not real happy with having to run it off an un-protected circuit, but there it is.


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## willburrrr2003 (Jun 18, 2011)

Ok, I build industrial control panels for a living in Seattle, WA. USA . If you are using a breaker with your VFD, only run the hot leg through the breaker. Make sure to have a good ground wire to your control panel. That being said, almost all of the major VFD manufacturers require FUSES ahead of the drive for protection, or they will not cover them under warranty. UL requirements call for fusing that limits the short circuit current possible though the device. All VFD's we wire are fused, since we are a UL shop. Fuse blow characteristics vs breaker, fuses will blow before a comparable breaker trips. Fuses offer equipment better protection for this reason as breakers let a bigger hit get to the equipment before the breaker trips. This is true of single phase power, and multiphase power. Verify which wire is your neutral wire, and which is your hot wire and wire accordingly.  As for a VFD blowing a GFCI breaker, if the settings are more aggresive in the VFD then the inrush current is way higher than the GFCI is rated for, causing it to trip. If you fuse your hot leg/s make sure that your using the proper fuse for the application too( some are time delay before blowing, some are quick blowing, etc....)

Regards,

  Will R.


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## lectrician (Jun 18, 2011)

I am an electrician by trade. 40 years experience. No doubt about it, you need to run a separate line to the lathe. be sure to pull a large green ground wire in the pipe along with the power.Same size as the power wires or better. Do not use a breaker, use fuses before the freque drive. there is no need for a GFCI if you bond that green wire directly to your lathe and the ground buss in your panel. Don't depend on the cord to ground the lathe. If possible it would be better to go with a 240 volt feed to the freque drive. Plugging that thing into an unknown plug in your house is a huge fire hazard. Any further questions, i work with freque drive all the time at work. i may be coming into 6 of them that convert 230 single phase to 480 three phase soon. The the company is going to throw them away.


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