Voltage has no real effect on efficiency unless the current is large enough to cause significant drop in wiring.

I'm guessing that this was a reference to 3-phase current being more efficient than single phase. For starting motors, this is correct, but I would expect that the operating cost differences to be negligible. Three phase motors themselves may be a bit less expensive than their single-phase cousins.

Higher voltage means less loss during transmission, but as Brickeye mentions, this is only a significant advantage over long distances or large current draws.

3-phase power was developed to allow transmission with minimal conductors. A 3-phase delta system can use only 3 conductors, and is limited by phase shift affects at longer distances, something that power engineering came to very late in the game compared to the higher frequency radio engineers.

3-phase motors have a non-zero starting torque and do not require supplementary hardware (centrifugal switches and capacitors) to start.

This can have an effect on larger motors, but below about 3 hp it is not very significant.

I'm curious about the "non-zero starting torque" statement........

Non-Zero? My debt is non-zero......;)

I know the caps and all...

Maybe a typo, but all starts have a bunch of torque....and everyhting running is torque, too.

Maybe I'm missing it.....

But overall, no, 208 vs 240, no big gain. Unless all you have available is one or the other. So to convert equip would cost more than effecieny gains.

KEN

A device such as a heater will use less power(watts) at 208 than it will at 240. I guess that makes it more economical. However it will need to run longer to create the same amount of BTUs.

"Maybe a typo, but all starts have a bunch of torque....and everyhting running is torque, too."

Single phase induction motors hacve ZERO starting torque.
A start winding with a capacitor to produce phase shift (a sort of second phase)is required for them to have a non-zero starting torque.

3-phase motors do not require any starting circuitry to produce torque at stall (not rotating) to start.
Some very large 3-phase motors have starting controls to limit the inrush current, but it has nothing to do with producing starting torque.

Ever seen a single phase motor with a blown starting capacitor?
It sits there and hums since it has zero starting torque and cannot start without the phase whift on the start winding.

Brick,

First off let me say I don't get around here often, so I'm like a newbie, but I've had the opportunity these past couple weeks,crazy schedule on our job, so if I'm annoying you, let me know. Anyway....

I get it, your just talking about the motor and fields, sure. NOT the mechanical load. But that terminology is cryptic. Non-zero is one of those almost oxymoronic terms that only engineers use, you aren't one are you? :)

ELECTRICALLY, and MAGNETICALLY, I THINK nonzero makes sense, but when you attach that motor to something and start it, there is real, measurable, physical torque being applied to the mechanical load, no?

That's all I was trying to figure out from the non-zero term.

KEN

A single phase induction motor has zero starting torque.
To overcome this problem the start winding and start capacitor are added.
This now allows the motor to produce starting torque.

They cannot start rotating without the cap and winding.

3-phase motors do not need any start circuitry. The presence of 3-phases allows them to start without any additional start winding or aphase shifting cap.

I know, I was only referring to the "non-zero" starting torque terminology.

What it means is that a sinle-phase wound motor, alone, cannot start rotating, there is no phase shift.

Non-zero is a silly term, if it's not zero, it must be "non-zero".

If the light is not off, it must be "non-off", right? :)

But, obvious a single phase motor would need to installed with starting aids, caps,flyweights, etc. etc.

So nobody would ever see one without this hardware unless they we're an engineer, or someone just fiddling around.

So, a single phase motor, with all the required accesories to get it rotating will generate torque on start-up.

I think a statement that says "Single-phase motors have no starting torque" is misleading. They do, if I take 2HP single phase motor out of something, with the cap still strapped and wired to it, and apply power it will jump. So that single phase motor has torque, no?

With out such assistance single phase motors would not exist.

I'm not trying to be facetious here, well maybe a little :), but I hate those foolish terms that are used for simple things.

And, oh, by the way, my taxes are NON-ZERO also.....

KEN

What is so hard to understand?
Single phase motors have zero starting torque, while "3-phase motors have a non-zero starting torque" and thus require NO special starting help.
You can make a steel ball spin in the stator of a 3-phase motor just by placing it there and applying power.

There are many other styles of motors that also have zero starting torque but they ae rarely encountered.

There are two general cases. Zero starting torque motors and non-zero starting torque motors.

It's just the "NON-ZERO" Thing, that's all.....

I had a laugh today, I was changing out a 240v, SINGLE PHASE 5Hp motor. In a really, really tough space, Now yes, THIS motor had zero starting torque, that's why it was being changed.

Incredibly, the replacement motor, a new 240v, SINGLE PHASE, 5HP motor, generated torque, ran the hydraulic pump, and the device worked fine. So this single phase motor, brand new out of the Leeson Box, generated torque, Good thing, too. My customer would not have been happy if I had installed one of those zero-starting torque motors.

I KNOW, IKNOW.....It's the NON ZERO THING.....

EVERYTHING IN THE UNIVERSE THAT IS NOT ZERO IS "NON_ZERO".

I weigh 185 pounds, if I gain 2 pounds, am I now NON-185?

But I am certainly non-zero pounds.

My truck weighs non-zero pounds, gets non-zero MPG, holds non-zero tools, costs non-zero to fill, makes me non-zero money, and gets non-zero parking tickets.

My number of posts here is non-zero. The energy used to type non-zero IS non-zero.

It's just the terminology, I understand the electrical, magnetic, and physical interactions.

Are you an engineer? It seems like it, you are stuck on the term.
Call the supply house and ask for ANY single phase motor they have available that has zero starting torque. While they are one the phone ask them for a meter that can read non-zero voltage.....

KEN

And I lost my P.S. somehow.......

The windings were open, I troubleshot it, so no, it was not a cap.......

I would have much rather swapped a cap in this weather, with where the motor was and all....

KEN

Any style of motor that has a zero starting torque requires added circuitry and parts to produce starting torque.
Single phase motors have ADDED PARTS to allow them to develop starting torque.

3-phase motors do not require ANY HELP or added hardware to start. They have non-zero starting torque, ion contrast with single phase motors, synchronouse motors, and a few others that have ZERO STARTING TORQUE without added hardware.

Why is that so hard to understand?
Motors can be divided into two groups.
This with ZERO starting torque, and those with NON-ZERO starting torque.
One type needs additional windings and devices to start, the other does not.

Open a start winding or remove the starting capacitor ADDED to SINGLE PHASE MOTORS since they have ZERO STARTING TORQUE by themselves and they sit there until burnout or thermal cuttoff doing no work.

Go search for the starting circuitry on a 3-phase motor.
Here is a hint, THERE IS NONE.
No caps, no switches, no extra windings.

Extremely large 3-phase motors have start up circuitry to limit the surge current and the shaft loading from quick starts. The hardware is there to REDUCE the starting torque.

"Extremely large 3-phase motors have start up circuitry to limit the surge current and the shaft loading from quick starts. The hardware is there to REDUCE the starting torque." Very true. Other added devices help reduce starting inrush current to lessen peak demand charges from the POCO or for other reasons. We had to go with soft-start on a motor powering a large flywheel for a 500 ton mechanical press with a flat belt. The motor without soft-start would spin up to speed while the belt would slip and burn due to the high inertia of the flywheel. Once up to speed, the system worked great.

What is so hard for YOU to understand?

I have said numerous times that I FULLY, and I mean FULLY understand how these motors, drives, components, etc work

IT IS ONLY THE "NON ZERO" TERM,

NON-ZERO is a stupid way to describe it, that's all. The engineer that came up with the term "non-zero" is stupid.

But I bet his salary is NON-ZERO.

I bet his IQ is NON-ZERO.

What is zero?
ZERO IS NOTHING>

True or false, Brick?

So anything and I mean anything that exists is non-zero..

True or false, Brick?

THAT MEANS EVERYTHING IN THE FREAKING UNIVERSE>>>>>
THAT'S IT>

Did you try to find a zero-starting torque motor at the supply house? Or order one online?

You are apparently hung up on "proving" you are right.

So yes you are right, everything is non-zero. Unless it is zero. Very DEEP>>>>>

KEN

This thread has turned very amusing. It seems Brickeye won't answer one of your pertinent questions. Is he an engineer? The answer is "yes". He has stated here before that he has a PhD in electrical engineering. So he has a non-zero degree.

"NON-ZERO is a stupid way to describe it, that's all. The engineer that came up with the term "non-zero" is stupid."

You area user of electric motors.
You do not design electric motors, and apparently have little knowledge about how thay are grouped into operating classes.

The use of 'non-zero' to describe motors that start without additional circuitry data at least to the 1920s, the earliest book on electrical engineering in my library.
It likely had use before then since published texts lag technology by a few years (though even this is decreasing).

I am a PhD PE.
I spent years designing electric motors for special applications (aircraft and other aerospace).

My degree is not important to the issue here, so I do not see how answering the question is germane.

You seem rather dense.

Motors with a non-zero starting torque do not need additional components added to start up (within th elimits even they have),

Motors with zero starting torque need added components, and when they fail the motor will not start to rotate.

If you do not like the terminology used by motor designers you can work on learning enough to become one and change the world.

If Non-Zero is such a "stupid" way to classify them then what term would you like to use instead?

Zero and non-zero make perfect sense to me in terms of the classification. I do not see other terms making the classification much simpler than that.

Let's see.

Maybe you could say.....

"Three phase motors have starting torque, and single phase motors do not."

Much simpler for us dense people to understand.

Thanks for calling me dense, by the way.And yes I am an end user of motors, I make a lot of money troubleshooting and replacing many components in fine pieces of equipment that engineers design, but never have to maintain,troubleshoot or repair in the field.

So in the intellectually challenged, dense world I live in: "non-zero starting torque" is a silly term.

"Has starting torque" makes a lot more sense.

Let's see, has PhD. or has non-zero PhDs they both mean the same thing?

Did the aircraft that your fine motors went into have lift or non-zero lift? Drag or non-zero drag? Thrust or non-zero thrust?

I bet it was "non-zero" all of the above, no?

So I'll go back to my little simple world and let you continue.

KEN

No point arguing with Brickeye. He is always right. And even if he is wrong he is always right.

bird, your comment is pointless in this instance. Brickeyee is correct in all his comments on this thread, this topic. It is dishonest to claim otherwise.

All specialized fields of human endeavor naturally develop specialized linguistics, as the intellects involved push into virgin territory.

At least in Engineering the purpose of the lingo is to increase both brevity and specificity, whereas the Legal and Medical professions, creating almost nothing new, simply restate the obvious in Latin, so they can then CHARGE YOU MORE, LOL! ;')

All this being said, why don't you have Brick come out and re-tap your transformer from 208, with his hot suit on.
I'm sure he'll find some non zero gains for you.

If his vintage 1920 books don't catch on fire from the Arc-Flash.

It's a fair rebuttal from being called dense...

When the last time time Brick cycled a breaker? Except for his A/C???

The field is much different than the lab.

We all work with the same stuff, but when you confuse people, they get hurt.

I bet the term HOT is different for engineers, than it is for us....Or is it non-not-hot? Oh that would be cold, I think... No, if it's non something than it must be that, so it would be non-cold. Wait.....If it is non-cold, than it is hot. Well I'd ask any guy in the field, can we work on it safely if it's non-cold?

That has been my point all along.

It's not intellectual superiority, it's terminology.

That was my point from my first post here..so say whatever you want...

So the engineers will continue to treat us like idiots.

I don't really care, most of the end users think engineers are idiots anyway. I almost always end up reworking their systems so they ACTUALLY WORK in my customers' REAL WORLD applications.

So when I see the eng's on the plant floor.........Oh wait I never do.......

KEN

Am I the only one who is puzzled as to why "kensnh" has been so offended by "brickeyee" using a trade term (non-zero)in response to a question? I'm sure there are terms that we all use that others might not readily understand. It doesn't mean we think everyone else is stupid. It also doesn't give others the right to be critical of our personal choice of terms. Especially when they're accepted as correct in the context they are used in. Ask a technical question, get a technical answer. Just my $.02.

EXACTLY>>>>>

In context?

This not an engineering forum is it?

No.
I thought it was pretty home-owners/DIYs/tradespeople exchanging questions and thoughts on problems that they are encountering in the real world.

I would venture to say that most people here will never have the need or desire to read engineering text from 1920.

So I would say my terminolgy is much more in context.

I never said "everyone else is stupid"

Actually Brick was insulting me. I asked about the terminology, and he instantly climbed up on his high horse spouting off as to why I was wrong, don't understand motors, and was dense, oh and think he told me to go read or learn more.

When in fact, I am not wrong. I just use terminology that most average people use. It just doesn't happen to be Brick's engineering language, so he MUST prove me wrong.

"Single Phase motors alone, without starting aids do not have starting torque" Is a CORRECT STATEMENT, and that's MY staatement.

So I may be dense, but I AM CORRECT.

Or is my statement incorrrect????

Brick, IS MY STATEMENT INCORRECT ???

YES OR NO?

If we were driving along, andI wanted you to turn right at the next intersection, should I say "turn right", or "turn non-right"? They are both correct, it's just that one is more easily understood than the other.

Gotta Go, non-zero customers waiting.........

KEN

All I can say is WOW!

The reason I asked this question is because our marina is changing to floating piers which means new electrical service. We have been told that they will not be using 240 (our current service) but will be putting in 208 voltage. The project engineer that the marina hired said it would be cheaper for the marina. They said they will be installing some buck type transformers on each pier. We were also wondering if phase converters might be required.

Many of the larger boat owners are concerned about burning out motors because they will be running slower with the 208.

Quit picking on Brick - he gives some of the best advice here.
Anyone know what happened to Pinocchio?
Gotta go - I'm making jumbo shrimp for lunch...

Pinocchio hasn't been around for a long time. I heard some lady took offense to one of his statements. It's too bad he was fun.