Using a ground as a neutral

[Wade Lippman]

The VFD on my 120v Jet 1642 lathe burnt up and I would like to replace it with a 240v VFD. (they are smaller, cheaper, and more dependable than 120v) The only problem is that the tach requires 120v. I can put it on a separate 120v circuit, but that seems so inelegant. I would like to run a hot and a ground to it. I am aware it is illegal, but millions of appliances are wired like that and no one ever gets hurt.

I ran a 120v circuit to it, but it draws less than the 10ma that is the minimum on my meter, so I don't know how much it uses but it can't be much. I then disconnected the neutral and attached that wire from the tach securely to the lathe. The lathe is on plastic pads, so I wired it to my drill press. I measured 121v and the the tach lit up normally. I disconnected the line to the drill press and put it on my leg and took my shoe off and put it on the floor. I felt a very vague tingle, but the tach did not light up; it measured 100v.
I reconnected the drill press and also connected it to my leg. There was no voltage and no tingle.
Finally, it occurred t me that the drill press was grounded through it's power cord rather than through the floor. (duh) So I connected the lathe to a chuck on the ground. The tach didn't light up.

I drew 4 conclusions from this:
1) The less than 10ma passed by the tach isn't particularly danger, even if worst came to worst.
2) The concrete floor isn't a good ground; at least not when it is dry.
3) If I wanted to cover all the bases, I could wire the lathe to the drill press (or something on a separate circuit, if the drill press isn't)
4) I have to get my lathe fixed because I obviously have too much time on my hands.

It seems to me that using the ground as a neutral is quite safe. I would be getting less than 10ma, probably much less.
I could connect the lathe to the drill press to avoid the issue, but that would create a ground loop. Would a ground loop under these circumstances matter?

Any comments (other than that I am a fool) would be welcome.
I did wear rubber soled shoes and gloves for all the testing.

[Bill Dufour]

Replace the tach or double the resistor in the meter. using ground as neutral is safe until it isn't. I forget the exact step but it is a simple undetectable broken ground lead can supply 120 volts to neutral and full amps.
What shoes, any socks, what is floor made of. Old old physics labs when electricity was just being studied had marble floors. Dry rubber horse stall mats would insulate the floor from electricity, fatigue and heat/cold.
Bill D

[Dan Friedrichs]

I think you have a number of profound misconceptions about electricity (e.g. concrete floor is clearly not going to conduct current), but I'll skip over those to answer your question.

You should buy a 240V to 120V transformer. That would allow you to do this safely. What you are proposing is not safe. Your tests show it may be safe, but don't consider likely failure conditions (e.g. what if something in the tach fails and causes it to draw >10mA?)

[Jim Koepke]

Being one who has done wiring and worked in the electronics field much of my life there is little advice I will offer people who are not trained in the field.

1. Don't do it if you don't know it.
2. Hire a professional.
3. What can go wrong will go wrong.
4. That, "I felt a very vague tingle," was just a warning. You may not survive the real thing. That little bit of extra wire to run a proper neutral will cost a lot less than any life lost from bad wiring.

There are good reasons for neutrals and grounds to be kept separate in home, shop and other wiring.

jtk

[Michael Schuch]

1) Find the power supply for the tachometer in the lathes wiring compartment. It might already be a 120v/240v power supply.
2) Replace the power supply for the tach. with one that is 120v/240v.
3) Replace the tach. with one that takes a separate power supply and use a 120v / 240v power supply. I know I paid less than $10 for my last electronic tachometer and used an old laptop power supply that was auto switch between 120v / 240v for the tach. You should be able to reuse the existing tach. sensor.
4) Buy another 110v VFD. They aren't that expensive.
5) Add a 240v - 120v transformer as suggested above.
6) Buy a NEMA L14-20P plug and receptacle. You get 2 hots, a neutral and a ground. You will have to add the neutral to your 220v outlet and wire it into the NEMA L14-20R receptacle.
7) Run a separate 110v power cable and a 220v power cable.
8) Give up having a tach.

I would never use a ground as a neutral! I understand the temptation of running a ground as a neutral. I have been tempted to do this before myself but ended up replacing the relays that had 120v coils with relays that had 240v coils in my RPC. The potential consequences just were not worth not doing a proper install.

[Maurice Mcmurry]

Ground and neutral should only be common at the main. Observing this rule is becoming more important.

[Andrew More]

Ground and neutral should only be common at the main. Observing this rule is becoming more important.

Further the neutral is relative to the 120V legs coming off the transformer, which is why there are three lines run into most US houses: 120V, 120V 180 degs from the first, and the Neutral which is between the two in the coils of the transformer. The two 120V legs are only 120V _relative_ to the neutral, and NOT the equipment ground. Which is why the Neutral is NOT the same as the ground. If you do NOT run a neutral the 120V legs will vary in the amount of actual power delivered and best case your equipment will stop working or run powerly. Worst case it will fail in a nasty fire.

[Brian Elfert]

It used to be common to use the ground as a neutral when an electrical item has both 240 and 120 volt parts in it. However, the NEC has required a separate neutral if a 240 volt electrical item has a 120 volt component for decades now. They realized it was not safe to use the ground as a neutral.

[Rod Sheridan]

Add a 240 to 120 control transformer to your installation or change to a 3 wire circuit…..Regards, Rod

[Bill Dufour]

I read 7 milliamps can stop the heart. It may or may not restart. A GFCI must trip at 5 milliamps or less.
Bill D.

[Curt Harms]

4) Buy another 110v VFD. They aren't that expensive.


That sounds like the simplest solution. Amazon has 'em starting at less than $100.

[Frank Pratt]

I can see a Darwin Award in OP's future. 'shakes head'

[Jim Becker]

The only two options I would entertain for this would be to either rewire the circuit properly for four wire 120/240v operation per code or replace the VFD with another 120v VFD.

[Rollie Meyers]

It used to be common to use the ground as a neutral when an electrical item has both 240 and 120 volt parts in it. However, the NEC has required a separate neutral if a 240 volt electrical item has a 120 volt component for decades now. They realized it was not safe to use the ground as a neutral.

It was only permitted to ground the frame of cooking appliances & clothes dryers to the neutral, up to when the 1996 NEC was adopted, now it is permitted in only in existing installations, it was NEVER permitted to use a grounding conductor as a grounded (neutral) conductor.

[Brian Elfert]

It was only permitted to ground the frame of cooking appliances & clothes dryers to the neutral, up to when the 1996 NEC was adopted, now it is permitted in only in existing installations, it was NEVER permitted to use a grounding conductor as a grounded (neutral) conductor.

Maybe I got it backwards, but they used to combine the functions of the neutral and ground in one wire. Someone in the past had installed a four wire range receptacle in my kitchen, but it was only wired with three wires. One of the connections on the receptacle had no wire connected. I ran a new four wire cable so the receptacle is connected properly now.

[Jim Koepke]

When young my father often had me along as a helper when installing washers & Dryers. In those days most wall outlets were two prong instead of the three prong grounded outlet. Also in those days plumbing was all metal pipe, coper or iron were the most common. He would install a clamp on the cold water pipe and run a wire to the washing machine & dryer when needed.

jtk

[Dan Friedrichs]

The old practice of connecting neutral to a range or dryer chassis was, like all code provisions, a risk balance - the belief was that, being very infrequently unplugged, a range or dryer was unlikely to have a break in the neutral wire, so it could provide both functions with an acceptable level of safety. With experience and new information, the risk calculus now concludes that the cost and inconvenience of a separate ground wire is justified.

[Bill Dufour]

When young my father often had me along as a helper when installing washers & Dryers. In those days most wall outlets were two prong instead of the three prong grounded outlet. Also in those days plumbing was all metal pipe, coper or iron were the most common. He would install a clamp on the cold water pipe and run a wire to the washing machine & dryer when needed.

jtk
I think up to the 70's a washer included the ground clamp. I do not think my dad would have bought a new one and know he used a new one for the last washer he bought.
Bill D

[Maurice Mcmurry]

When the center tap of a transformer is zero volts, it is not a ground or vice versa. My Brit and European friends say "American 120 volt circuits are a cheat".

[Jim Koepke]

One problem of the neutral wire is it can have a voltage different than the ground.

Even though at some point the ground and neutral are bonded the distance from ground, an imbalanced load and the distance to the bond to ground can add up to an uncomfortable if not dangerous situation if one happens to be touching a stove while turning on the water.

jtk

[Frank Pratt]

It was only permitted to ground the frame of cooking appliances & clothes dryers to the neutral, up to when the 1996 NEC was adopted, now it is permitted in only in existing installations, it was NEVER permitted to use a grounding conductor as a grounded (neutral) conductor.

And that's an exception that never should have been allowed. I'd love to hear a good reason why it was, but I don't think one exists.

[Frank Pratt]

When the center tap of a transformer is zero volts, it is not a ground or vice versa. My Brit and European friends say "American 120 volt circuits are a cheat".

And they'd be dead wrong. The theory and implementation of the Edison 3-wire system is solid and safe.

[Bill Dufour]

And that's an exception that never should have been allowed. I'd love to hear a good reason why it was, but I don't think one exists.

Houses did not have a ground wire up until the 1960's. There is no good way to run a ground to an existing outlet clear from the panel. It was probably safer to use the neutral then to have no ground at all. I do not think you are allowed to tie a ground wire to the metal gas pipe on a stove?
Bill D

[Jim Koepke]

And that's an exception that never should have been allowed. I'd love to hear a good reason why it was, but I don't think one exists.

There may not be a good reason. The only thing that comes to mind is if the code at the time had neutrals tied to ground at the entry panel to homes.

jtk

[Brian Elfert]

And that's an exception that never should have been allowed. I'd love to hear a good reason why it was, but I don't think one exists.

I am thinking cost may have been an issue, but someone else mentioned that houses did not have grounds in the old days. I looked at an older house (1950s maybe?) for sale on a very large city lot and realized it did not have grounded receptacles. That was certainly one reason I decided the house was not for me.

[Andrew More]

The ground has always been a safety feature. A way to route a short into the earth, rather than shocking people or causing fire. This is the reason why you did not learn about the ground wire in high school science class, it's not part of the circuit, the hot and neutral are.

Further to have the ground wire work correctly the following factors need to come into play: there must be a short and the shorted wire must come into contact with some grounded part of the device. With today's modern plastic framed devices the likelihood of a failure of this nature becomes very unlikely. There just isn't any expose metal for people to touch.

That having been said, it's better to have it than not, since the cost with modern romex is relatively inexpensive. In the early days of Knob and Tube, running another wire was much more expensive, because they were much more careful about the way the wires were run: separated by about 6", each with an independent (hand drilled) hole, each hole with a ceramic insert, and all connections soldered together. With the move to all the wires together though a single hole, power tools to drill the holes, no ceramic insulators, and using wirenuts instead of solder it's become much much cheaper to run wires. The gauge of the wire is the same.

I honestly don't know which system is safer, I can't imagine the removal of ceramic insulators, soldering wires as an improvement. The distance between the wires in the old system makes animal problems less likely to occur. Generally speaking the issues with knob and tube are that it's old. Almost all the other issues, other than a lack of ground wire also happen with modern romex: people messing with it, overloading the circuit, shorts, etc.

[Brian Elfert]

Many of the problems with knob & tube come from people, especially unqualified homeowners, making changes or additions to the knob & tube wiring. It is not uncommon to see modern NM-B (Romex) cable spliced into a K&T circuit to extend the circuit. People try to run a modern household off of old K&T wiring and they often overload it. A house with K&T will often still have a fuse panel and people just install larger fuses when fuses blow due to circuit overload.

A new house wired to 2017 or 2020 NEC will very rarely have overloaded circuits as the code requires a lot more circuits these days. Lighting loads are decreasing due to LED lighting. Modern HVAC means it is very rare anyone will be plugging in a window A/C unit these days, nor a space heater. I ran a new dedicated 20 amp circuit to my bathroom in 2014. Last week the breaker tripped and pretty sure an electric toothbrush isn't going to overload a 20 amp circuit. I never did figure out why it tripped. My breaker panel was new in 2020 and all of the breakers are new since 2014.

[Andrew More]

Yes, like I said, overloading circuits and people doing dumb things is not limited to K&T.

Your breaker could be tripping because it's a GFCI or AFCI. Both are far more sensitive than older breakers, and they've started requiring them in modern panels.

[Bill Dufour]

K&T the wire is not always insulated. Not good to lean an aluminum ladder against it. or hang a metal coathanger over it. Obviously the power companies still use K&T it since no plastic insulation can withstand the high voltage in the sun and rain of a power pole.
Bill D

link is 230Kv insulator

[Lee Schierer]

K&T the wire is not always insulated. Not good to lean an aluminum ladder against it. or hang a metal coathanger over it. Obviously the power companies still use K&T it since no plastic insulation can withstand the high voltage in the sun and rain of a power pole.
Bill D

link is 230Kv insulator

K&T was originally insulated, but with time and critter help the insulation falls off. All the K&T I have encountered has been 14 gauge wire. It is not a good idea to leave it in place. My sister owned a house that supposedly had all the K&T replaced. What we found was the easily accessible wiring was replaced, but wiring in the walls was still K&T. They even pig tailed new outlets on romex that was tied into K&T behind the outlet box. Some was on 20 amp breakers. My Dad and I ran new runs to avoid the patch work and pulled out what was done wrong that we could reach.

[Ronald Blue]

K&T was originally insulated, but with time and critter help the insulation falls off. All the K&T I have encountered has been 14 gauge wire. It is not a good idea to leave it in place. My sister owned a house that supposedly had all the K&T replaced. What we found was the easily accessible wiring was replaced, but wiring in the walls was still K&T. They even pig tailed new outlets on romex that was tied into K&T behind the outlet box. Some was on 20 amp breakers. My Dad and I ran new runs to avoid the patch work and pulled out what was done wrong that we could reach.

I definitely remember when there was insulation on overhead powerlines. As you say over time the elements and critters took care of it. To add to that there used to be a factory near me and it was called "porcelain" that made all sorts of insulators for power transmission. In the later years it was owned by McGraw Edison and then became Cooper Power Systems. They made some pretty large insulators as I recall.

[Andrew More]

K&T was originally insulated, but with time and critter help the insulation falls off. All the K&T I have encountered has been 14 gauge wire. It is not a good idea to leave it in place.

I honestly think this depends on the wire. Like to much about old houses there are things that are fine, since the house keeps out the weather, and things that are not. The insulation on the wires in my 100 year old house was all fine, but obviously YMMV. Even if it gets worn bare the rest of the system is setup to handle this. I'm not sure what the degradation of romex is going to be in 100 years. In theory it's going to be fine, since it's plastic, and plastics never die, but we'll see.

The issue with removing it is that most things are fine until somebody messes with them, and then there are problems. I'd love to see some stats on how often electrical problems are caused by people changing things vs other types of problems, like things degrading over time.

The other big issue is that I do NOT believe you can get insurance for a house where you admit to having K&T. If you just don't ask, don't tell, you can usually get insurance, but if you say "I know it's got some Knob and Tube" they'll refuse to insure. At least that was my experience a couple of years ago calling around to just about every insurance company I could get ahold of. Which is interesting, because I know the town I live in has to have a large amount of K&T (oh and usually few fires).

I'm wondering if some insurance agencies aren't planning to collect the fees and then to refuse to pay citing K&T wiring. You just don't know.

Which is why I've removed all of mine.

[Brian Elfert]

Your breaker could be tripping because it's a GFCI or AFCI. Both are far more sensitive than older breakers, and they've started requiring them in modern panels.

I believe it is a standard breaker as my memory is that AFCI was not required for bathroom receptacle circuits under the 2014 NEC. It has only tripped the one time since I installed the circuit in 2014.

[Brian Elfert]

I have 40 year old NM (Romex) cable pulled out of my house that the insulation and wire still seems just fine. I scrap most of it because it is NM not NM-B. The removed lengths are not all that long so it makes sense just to spend a few bucks on new NM-B cable.

[Rollie Meyers]

And that's an exception that never should have been allowed. I'd love to hear a good reason why it was, but I don't think one exists.

Have heard it was a wartime effort to save wire, the exception allowing it should have been removed decades prior to the 1996 NEC where it finally changed.



Houses did not have a ground wire up until the 1960's. There is no good way to run a ground to an existing outlet clear from the panel. It was probably safer to use the neutral then to have no ground at all. I do not think you are allowed to tie a ground wire to the metal gas pipe on a stove?
Bill D

Absolutely not permitted to ground through a gas line, metallic gas piping is bonded to the metallic water lines, while I don't know how other utilities do it, PG&E does have a nonmetallic bushing to electrically isolate the customers lines from theirs, may not be as important in the future as the metal UG lines are replaced with nonmetallic piping.

[Jerry Bruette]

Absolutely not permitted to ground through a gas line, metallic gas piping is bonded to the metallic water lines, while I don't know how other utilities do it, PG&E does have a nonmetallic bushing to electrically isolate the customers lines from theirs, may not be as important in the future as the metal UG lines are replaced with nonmetallic piping.

When our house was built I questioned the ground wire on the gas line because I knew the line that was feeding the meter was plastic. I was told that the ground wire was to ground the metal gas lines in my house to the panel, in case they somehow came in contact with a live wire. It made sense to me.

[Wade Lippman]

I read 7 milliamps can stop the heart. It may or may not restart. A GFCI must trip at 5 milliamps or less.
Bill D.

Then I guess I am lucky to only have 0.6ma. A neighbor had a ammeter capable of measuring it. Only 8 times stronger and it would trip a GFCI!

[Frank Pratt]

One problem of the neutral wire is it can have a voltage different than the ground.

Even though at some point the ground and neutral are bonded the distance from ground, an imbalanced load and the distance to the bond to ground can add up to an uncomfortable if not dangerous situation if one happens to be touching a stove while turning on the water.

jtk

The fact that you felt any tingle at all should have warned you that the idea was stupid and dangerous. You sir, should not be playing around with electricity.

[Andrew Pitonyak]

Houses did not have a ground wire up until the 1960's. There is no good way to run a ground to an existing outlet clear from the panel. It was probably safer to use the neutral then to have no ground at all. I do not think you are allowed to tie a ground wire to the metal gas pipe on a stove?
Bill D

I was visiting a friend in the early 90's and he mentioned that he had paid an electrician to install some three prong outlets since his house had only two prong. He then told me what he paid and I said "he did not run a ground" and my friend insisted that the electrician had. I opened up an outlet and sure enough, the electrician had simply tied neutral to the ground in the outlet.

[Frank Pratt]

I was visiting a friend in the early 90's and he mentioned that he had paid an electrician to install some three prong outlets since his house had only two prong. He then told me what he paid and I said "he did not run a ground" and my friend insisted that the electrician had. I opened up an outlet and sure enough, the electrician had simply tied neutral to the ground in the outlet.

Yikes! Was that a real electrician or one of those home handy person types? I sincerely hope your friend either got his money back or had the "electrician" correct his mistake.

I Canada code requires that the circuit be put on a GFCI on an ungrounded circuit if old 2 prong receptacles are replaced with 3 prong.

[Maurice Mcmurry]

I have worked on several old knob and tube wired houses in town that were upgraded with 3 prong grounded receptacles with the neutral daisy chained to the ground. It is a technique some old-timers embraced for a while. I was asked to see about removing a window AC from a 2nd story window that had a history of shocking people. It was plugged into one of these "upgraded" plugs that had reverse polarity. The steel case had 120 volts to ground. A siding guy had been shocked and was not happy.

[Jim Koepke]

It was plugged into one of these "upgraded" plugs that had reverse polarity.

Probably not many here who remember or even know about the AC/DC radios that were common into the 1960s. They were usually five tubes with filaments wired in series so they didn't need a transformer. Usually the plugs were unpolarized. If reception was poor flipping the plug would often clear it up. One side of the cord was grounded to the chassis. One could get a nasty sting from one of these missing a knob if it was plugged in with the hot side of the line going to the chassis.

jtk

[Charlie Velasquez]

Yikes! Was that a real electrician or one of those home handy person types? I sincerely hope your friend either got his money back or had the "electrician" correct his mistake.

I Canada code requires that the circuit be put on a GFCI on an ungrounded circuit if old 2 prong receptacles are replaced with 3 prong.

Also, here. It must also be labeled as “GROUND FAULTED, NOT GROUNDED” and no ground wire is allowed if you add additional 3-prong receptacles downstream (and every downstream receptacle must also be labeled as ground faulted, not grounded).