Wiring a pair of 15 amp vacuum motors.

The only reason I don't have an induction furnace at my house is because the utility company transformer behind my house is tiny, and it feeds two houses.
I could work around the 1-phase/3-phase problem if I had sufficient capacity in the transformer.

Edit:
There was a guy on the other forum who solved the problem by running his induction furnace from a 3-phase, 480 volt genset.
If I had a 480 volt genset, I would have a nice induction furnace.
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I have a 55 kVA transformer that I share with four neighbors. I just have to be mindful around dinner time. I have a 15 kVA auto transformer and 20hp rotary phase converter. It is pretty safe. It’s all placed on A 60 amp GFCI breaker.

 

And the thing to remember too is that the importance of a UL label on a device is to prove that the device has been tested under some very severe and abnormal operating conditions, and has been proven not to fail catastrophically.

I don't buy anything (or spec anything) that does not have a UL label on it.

And often contractors will offer to modify a piece of equipment in the field, for various reasons, and neither I nor the manufacturer allows that because that opens you up to a potential failure and lawsuit if things don't work right.

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I have seen and specified some solid state and rotary converters, and they work well assuming you don't overload something.

The Chief Electrical Inspector for the city I live in asked me one day "Do you follow the National Electrical Code?".
I said no, I follow "Pat's Code".
He said "What the heck is Pat's Code", and I said Pat's Code is "don't let it overheat, burn up, blow up, or hurt anyone for any reason".

The Code is the bare minimum that is considered safe, but I consider much of the Code to be unsafe, especially in industrial applications, because it is just not rugged enough, and does not have enough safety factor.
The NEC is more geared towards residential stuff.

I use the IEEE standards for medium voltage design.

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Like I said in a previous post, if the two motors have about the same impedance, then if they are wired in series, the neutral current should be close to zero.
If the impedance varies significantly, then the voltage across each motor will not be 120 volts, but will be more than 120 volts on one motor and less than 120 volts on the other.

The neutral will carry the difference in the balance between the two motors as far as impedance, and I guess carry the difference in amps from varying loads on each motor.
(I think I am repeating what Matt has already stated).

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OK, I need more clarification here, and I'm not being contentious.

In every residential service entrance panel I have seen, which we call the breaker box, there is one terminal strip to which all white wires (neutral) and all ground wires are tied. I assume this is the bus you are referring to. This strip is also tied to the enclosure, and usually has a tie to an exterior ground rod. All 120v circuits carry the full current through the neutral wire, so when they are carrying current they are tied to all the ground wires at the panel. Those that are on different legs cancel each other out, but you can be sure there is current running through the neutral/ground bus most all the time. How is that different than using the ground as a conductor so far as the panel box being energized? I don't use ground wires as conductors, but with them all being tied together I can't understand your statement that you only get in danger when grounds are used as conductors. To me, you only get in danger when there is a failure of the connection from the terminal strip back to the meter/transformer. The neutrals are just as live as the grounds. It has also seemed funny to me to feed power back through all the ground conductors if the neutral connection back to the meter fails.

See what I mean?

 

Electricity finds the way of least resistance. Even In the main entrance (to the first panel) the buss ground and neutral are tied. The neutral finds its way into ground rods, into your waterline, into your natural gas pipe, back to the pole which has a ground rod at it and even the transformer pole or ground transformer has ground rods .

You should never have or get voltage or amperage on any ground lines from outlets to panel. This is why it is a severe a no-no to ever Bond common to ground in any sub panels after the main entrance.

Using the ground as neutral totally works but it puts voltage on it, and if it is part of a branch, it charges the ground wire as a hot within that branch. Ground should only be used as a safety or a fault.

Just imagine One of the hot wires on your table saw motor fries and touches the motor housing transferring power through out your whole machine (as your whole machine is all cast-iron and grounded) this would become a dead short and throw the breaker. But if you’re using the ground as a neutral, while using it as the neutral it is hot along with the rest of that branch circuit. So you’re using the tablesaw and your wife is using the electric weedeater on the same circuit and she’s in a little bit of wet grass and she was wondering why she’s getting a shock well touching the aluminum headstock.

 

Pat you are completely correct on the above statement along with the assumption that if one motor has a different impedance than the other. The mutual connection point between the two will be at a potential that is not at neutral reference to service ground. If this point is connected to earth ground. It will draw current through the earth ground attempting to bring the voltage to the potential of earth or at least earth potential as is introduced at the point of earth contact.
I will agree with everything you have said about the ground. It is not , supposedly carrying current Unfortunately, earth is not a perfect nor is it in many cases even a good conductor. It answers to ohms law. Just because you have multiple points to earth ground at some distance apart does not make them at the same potential. Think step voltage. If a 110 circuit is used to carry current. There will be a voltage potential on the ground wire. In a proper installation this might only be micro volts but it is there. In bad situations such as excessive leakage voltage to ground or where heavy capacitive coupling occurs this voltage can become problematic and in rare occasions be dangerous. When dealing with voltage sensitive equipment such as bio monitors or anything that must detect very low voltages in the micro volt or lower range anything over .5 VAC will stop a project cold until the problem can be corrected
O,O,O! The age old question of weather 220 VAC or 2 - 110 VAC 180 out of phase lines are 2 phase or one. This argument goes back as far as or before Tesla or Edison! Granted it is derived from 1 leg of a 3 phase system. It is true 2 phase just as 3 phase has a neutral point that pushes in 3- 120 degree phases from a neutral point to a peak. 2 phase 220 pushes from 1 neutral pint in 2 directions at 180 degrees opposing each other. It is true 2 phase. It is not 2 phase as referred back to the phase potential produced by the utility but it is true 2 phase.
Joe

 

There are strange connections where the earth is used as one of the conductors, such as high voltage DC transmission lines, were often only a single conductor is strung on a pole line.
But generally, the ground rod at the electrical service entrance is for overvoltage during lightning strikes.

I can't recall if my house panelboard has an insulated neutral out to the utility transformer, but in general design, such as with a 3-phase pad mounted transformer, you bring in three insulated conductors (phase A, B and C), and also bring in one insulated neutral conductor (for a 480Y/277 or 208Y/120 volt system).
You do not run a ground conductor from the service entrance panel to a pad mounted transformer, since it would parallel the neutral.

The secondary transformer Y centerpoint in a pad mounted transformer is grounded at the transformer via a ground rod.
So technically you could flow some current through the earth from the transformer ground rod to the service entrance panel ground rod, but it would be small since there is a low impedance path in the form of the insulated neutral conductor.

I am pretty sure all typical US houses use a 3-wire service drop.
For an overhead service this is two insulated conductors, and one un-insulated neutral conductor.
For an underground residential service, I also assume that there are 3 wires, but I can't recall if the neutral is insulated or not.
It would be best to have the neutral insulated, and in industrial work it would be.

The ground bus in a panelboard is bonded electrically to the enclosure.
The neutral bus in a panelboard is insulated from the enclosure, but with a residential panelboard, there is typically a screw that can be inserted to bond the neutral bus to the panelboard enclosure for service entrances only.

Bonding the neutral and ground busses in the service entrance panelboard does not cause current flow between any load and the ground bus via ground wires.
The ground wires only see current during fault conditions.
The ground wires are only connected to metal enclosures, metal conduit, metal fittings, etc., they are not connected to motor leads, etc.

If you use a bare ground conductor as a neutral,, such as in a 120 volt circuit, then it will carry full load amperage, and have 120 volts on it under normal operation, and anything that this bare ground conductor touches will be energized with 120 volts (panelboard, conduit, fitting, people, etc.).

You have to think of it as a difference in potential with respect to what.
While there may be little or no difference in potential between a neutral and ground conductor, one carries normal operating current (the neutral), and one does not (the ground) (in a branch circuit).

I guess technically you could conduct electricity from a grounded enclosure through the earth and back to the neutral point on the pole mounted transformer via the ground rod at the transformer, but the impedance of the earth in that circuit would be so high compared to the path from the bonded neutral/ground busses in the service entrance panel that I don't think it would be significant.

Another point in using a ground conductors and a ground rod at the service entrance is to keep all the non-current carrying parts in an electrical system at the same potential, and keep these parts also at the same potential as the earth outside.

If something goes wrong with part of your service entrance panel or the service entrance wires that connect to it, then all heck can break lose.
I have heard about such conditions, and depending on exactly what happens, you can get all sorts of overvoltages and overcurrents.

If the service entrance neutral conductor is removed, then the loads on one line will try to feed through the loads on the other line.
The load on the two lines will never be the same, so you will get some very strange voltages occurring.

Edit:
How do I keep it all straight in my head with the various electrical distribution systems?
I don't use non-standard electrical systems, I don't use non-standard electrical connections, I don't use non-standard non-UL electrical devices, and I always use exactly the same grounding configuration as it applies to each system, per the National Electric Code.

Edit02:
When you design an outdoor utility substation, you have typically a 4/0 conductor in the ground, laid out in a grid configuration, that bonds the metal fence, the support structure, the operating handles, metal enclosures, and you use metal ground pads to stand on when operating the handles, and the ground pads are also tied to the 4/0 ground grid.
Even then, the voltage drop from the switch handle to the ground grid you are standing on, during a fault condition, may be enough to kill you.
All the metal and the fence at the substation must be grounded multiple times to the ground grid.

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If you wrap your head around electricity distribution like a drop of water... for every drop of water that is sent out, one drop of water has to come back on the other hot or the neutral line. A ground fault circuit interrupter breaker does this to .06 A. All voltage and amperage needs to come back on the hotlines or the neutral line to the main panel. If it doesn’t, the breaker trips and everybody is happy and safe. Not all circuits have GFCI breakers. But if you can imagine that they did… and wire accordingly, it will be pretty safe.

 

I thought I could leave this alone but I just can't.

In understand industrial power. We used to jump onto a motor circuit to hook up our 8-packs during an outage. It is a whole different world.

But this discussion is all residential. Kelly's garage is part of his residential service, I'm sure.

My shop has only a 200 amp residential service.

I am not advocating using a ground as a conductor. Kelly was going to use two identical motors (15 amp) and we had suggested he could do that with 3/wg, running one phase to one motor and one phase to the other then using the third conductor as neutral. If he uses a 220v breaker when one motor is running the neutral carries the load. When the second motor is running the neutral carries practically no load. After several posts indicating that was wrong, and claiming the motors are in series and that is a bad thing, that is now accepted as OK.

Then the discussion digressed as to how bad it is to use a ground as a conductor. In my house, and every house I have lived in, and worked on the breaker box (and there are no branch circuits in any house I have seen) every single one has only one terminal strip used as a common neutral and ground bus. So any unbalanced load being conducted back through the neutral to the utility energizes the terminal strip, box, and every ground lead in the entire house.

If one were to use a bare ground as a neutral it energizes nothing that the common neutrals have not already energized other than there is current in that one bare so a slight potential at the load connection. Residential. Romex. No conduit. I can touch the "live" bare neutral and not get shocked because it only has the potential from the load to the breaker box. I am not toast. My breaker box enclosure has the same potential whether load is on the bare grounds or the insulated commons. What am I missing?

One terminal strip, no optional bonding.

 

Many residential panelboards use a common bus for neutral and ground.
I don't care for that because it makes one side of the panelboard enclosure too tight with wiring, while the other side is empty.
I use a ground bus on one side and a neutral bus on the other.
I consider a messy panel a more dangerous panel, just like a messy shop is more dangerous than a clean one.
But people who wire houses are not exactly rocket scientists, so there is that.
And what they do does work, so that is all the proof they need to convince them that they must be doing it right.

I have discovered over and over again that you can lead a horse to water, but you cannot make him drink it.
Blessed are the few who are open to change, but they are rare like snow in hell.

But the statement in the quote above is incorrect.
Look at the path of current flow.
If you use a ground conductor on the right side of your house as a neutral, and your panelboard is on the left side of your house, then you have 120 VAC and full load current trying to flow across your house back to the panelboard, and through any metal or people that touch that conductor.

If the ground is insulated, you eliminate that path of conduction.

Its extremely dangerous to use a ground as a neutral, and the potential for electrocution is high.

The fact that the neutral and ground conductors are bonded in the service panel does not cause any current flow in the bare ground conductors in the house, and so there is no hazard with doing this.

Its a bit confusing, I know.

You have to look at current flow.
Current flows in a loop, from the pole or pad mounted transformer to the house, to the load, and then back to the transformer.
If you want to see a circuit clearly, draw the complete loop, and then seen if you can insert yourself in that loop by touching a ground wire in your house.

You also have to look at potential.
Has a bare ground wire been elevated to a 120 VAC potential?
If there is no potential, then there can be no current flow.
Again a loop diagram will tell the story.

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Well put, Pat. Since you separate common and ground you assumed everyone else did too. And they don't.

Since each circuit is run from the breaker to a series of outlets or lighting boxes, the bare ground does go across the house. But the voltage drop in a 14 ga at 10 amps for 100 ft is only 5 volts. When everybody else connects the common and ground at the breaker box you're seeing 5 volts at the load, on the ground if it's being used, and even with 10 amps of 120v 5 volts is not going to shock you by contacting the ground wire improperly used as a conductor. 15 amps is a whopping 7-1/2 volts. I live on the edge, I even touch both terminals of a 12v DC high amperage source. Electrocution danger is not high unless there is an open circuit.

If I'm adding circuits in a live box I do so freely after verifying there is minimal voltage on the terminal strip. Connect the white and ground to the strip and plug in the terminated breaker. I suspect you shut off the main breaker and pull the meter. That is also safe.

I have discovered over and over again that you can lead a horse to water, but you cannot make him drink it.
Blessed are the few who are open to change, but they are rare like snow in hell.

 

Generally I do not, but that is not to say I do things in a completely safe way either.
And not to say that because I do unsafe things, then others can do unsafe things and not get hurt.

The medium voltage linemen in this area use to work all the overhead medium voltage lines hot, using insulating gloves.
They finally fried enough linemen that they got away from that method.

Everyone has to find their comfortable level of safety, but the key is to be able to do whatever in a safe manner every time.
You generally do not have a defibrillator laying around in case a wire has a bare spot on it while you are reaching into the panelboard.

The thing that concerns me more is a medium voltage switchgear failure while I am in the vicinity of it.
I am often around that gear.
They make new switchgear with arc chutes to contain the arc blast, but it is seldom used due to the outside ducting that is required.
I don't mind dying, but I don't really want to be half vaporized during an arc flash, and most medium voltage switchgear will not contain a major arc flash.

I was around the 5KV switchgear below only days before it blew up.
Arc flashes can be like 30,000 F.
It wasn't my time I guess.

 

Even 480 we stand to the side to energize.

I’m happy to be retired, was never burned in refinery work but was plenty close several times.

Refinery training still affects my daily activities.

 

At one point I considered getting on with the local refinery, but it seemed risky the way they set it up so that you were an independent contractor.
It turned out to be true; they roasted several a few years ago when they were trying to repair a leak.

I knew a guy who did the electrical maintenance for the local foundry.
I have great respect for that guy.
He showed me a motor that was like 64,000 hp (a blower).
They brought 161 KV right into their plant, tapped right off of the transmission line (very rare).

And another guy I worked with worked at the local refinery, and he said one night he looked out of the lab, and there was a fireball covering the sky.
He said he ran like heck, and never looked back.
His boss chastised him for not staying and fighting the fire.
He quit shortly after that.

You can make good money if you can safely accept some risk.
The more risk, the more money.
Much like gambling, but I consider the odds much better with engineering (usually).

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Which refinery is that?

I was managing a turnaround in the HF Alky and had stayed over until about 8:00PM walking toward the job when a heater blew up about 100 ft away. Straight up, flames over 200 ft high (next to the DIB tower for reference) and contractors on my crew scrambling to get away. I kept walking toward the fire trying to slow people down to avoid injuries (there were none at all, just laundry issues) when one of my employees ran into me running toward the fire. He got to a fire monitor 50 ft away from the heater and turned it onto the fire then the heat drove him back. We were serious about safety and my boss wanted to discipline him for approaching the fire even though he was a member of the fire brigade. Management thinking.

We had a 69 kv running a 15,000 hp compressor and had to call the utility for a coordinated start. Starting the compressor would make the conductors wiggle violently in sinusoidal waves. A process engineer tried to get me fired. We were in the gear house inspecting the new installation (tourist inspection) when he pushed a button like an idiot and we could hear the compressor whine and start to spin down. Within in two seconds I hit both start buttons and it stayed up. We went back to the control room to sign out expecting to get an ass eating. Nobody noticed. The night shift would kick it off and restart without calling the utility. The operations manager lived close by and his CRT TV picture would get really small. He would go straight to the plant and eat them out. PSO always covered him, it never knocked the line down that I know of.

 

Odds better with engineering:

In the Soviet Union after a bridge inspection the bridge would be loaded with gravel trucks to proof test it, with the engineer standing under it.

 

I can't mention the name for liability reasons, but I think it is a situation that has happened at one time or another at almost all refineries.
Refineries are risky business.
Any business that pushes that much energy around and through a product is a risky business by nature.

True Story:
I worked with a structural engineer who was previously a co-owner of his own firm.
The designed a large tramway over a river, and one afternoon his partner called him right at 5:00 P.M. and said that he had found a problem with the structural design of the tramway supports, but it was late and they would discuss it in the morning.
His partner died of a heart attack that night.

My co-worker said he reviewed every design detail and could find nothing wrong.
When they built the tram, they loaded it up with a massive amount of sandbags.
The structural engineer was there, and he said "I want to ride across during the first test with sand".
The installer said "If something goes wrong, you could die".
The engineer said "If something goes wrong, I don't want to be around".
So they let him be the first passenger, and with a full load of sand.

It did not fall, and is still in use to this day.


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