Hello all,
A friend dropped by the other day and was describing the way his woodworking machines had been wired by a friend from a 3 phase supply.
Apparently the friend had used two legs of a 3 phase supply to provide 220v
power for the 220v machines.
To me this sounds a bit fishy. Isn’t 3 phase rather different from Single phase?
Even if you used 2 legs to achieve 220v wouldn’t the phase cycle be off from what the Single phase motor is designed for??
Thank you in advance for your thoughts!
Tom
Replies
There are a few different configurations for 3-phase, but a common one will give you 208V between any two hots, which is often used for "220V" tools.
This supply will also give you 120V from any hot to ground.
In a nutshell this is done all the time. Any two legs will give you the phase to phase voltage either 208 if it's a "Wye" transformer or 240 if it's a "Delta" connection. The trick is to balance the loads within 10% across all three phases so that A-B, B-C & A-C all have about the same load. If he has several loads and a 3 phase panel board it's easily done. Any large office building you go into will have the lighting and non-motor load wired this way. On a 208/120V system any one phase to neutral will give you 120V (nom.). Where you have to be very careful is on 240/120V, 3 phase "Delta" systems. 2 of the phase conductors will give you 120V, the third will give you 170V. Bad news, that's why it's called the "stinger" or high leg.
John O'Connell - JKO Handcrafted Woodworking
Life is tough. It's tougher if you're stupid - John Wayne
IronDog, that's the way my MiniMax jointer and planer are both done. They each have a 4.8 hp three phase motor and my shop is all single phase. The motors each have a "start up" capicator and a "run capicator". Evidently there is a limit to the size motor that can be done this way as these were the largest motors available to be run on single phase. If I had had three phase available to my shop ( it would have cost me $10,000 to have the electric company run four spans from the nearby elementary school) I could have had 9hp three phase motors for the same price.
Bill Lindau
Hi everyone,
Thanks for the responses to date. I think I'm learning a bit here.
A more recent development from my friend setting up his shop using
3 phase to power his 220 machines. All the woodworking machines
seem to be working just fine. Yesterday he hooked up a welder that uses 220.
It has a little display screen and a microprocessor. The screen displayed a message saying that the voltage was unacceptable ( I'm paraphrasing ).
In other words the welder wouldn't accept the two legs of the 3 phase for some reason.
I imagine that welders are more sensitive to the specifics of the current and phases and cycles? I know this is getting out of range of woodworking but we
all use ( almost all ) electricity to do what we do.
Tom
More than likely he is using the wrong leg for his welder(220 single phase, right?). He needs to be using the two origional legs that come in from the power service, not the generated leg from the phase converter. Make sure any magnetic switches/controlers are not run on the converted leg either. The way I have prevented this problem was to run all my cords in the same color scheme and they are always connected to the same "X,Y,Z" on the recepticles and plug terminals. I always run the converted leg in blue and the 2 original legs in red and black. If the motor runs the wrong direction, switch only the black and red wires, not the blue. This switching is usually done at the machine, not in the connections in the cords, recepticles, or conduit. Makes moving machines around alot easier. This is for 220 three phase. Any 220 single phase is run with orange wire. Doing this also helps keep the panel load balanced.
Also, I'm assuming he is using a rotary converter. If it is a static converter, he needs to be careful on some types of motors. Some motors take a "constant direct load" as in power feeders. If this is the case, he'll burn it up and they are not cheap to have rewound.
I spent the last week wiring my shop, hopefully for the last time. I never want to move/build again
Hi Migraine,
I think the thread has gotten a bit confused since the first post.
The power supply in discussion is 3 phase. But, it is "real" 3 phase from the power companies transformer - it is not from a phase converter.
Hope that explains it. I'm just asking for opinions and trying to learn something myself. And trying to make sure my friends machines, which are 220v single phase and now running off 2 legs of a 3 phase supply, will not damage the motors over time.
Tom
Dear IronDog,
As you say, all utilities produce and distribute 3- phase power. Thus, the electricity in our homes is also taken from 'legs' of a 3 phase distribution system, even if service is 'single-phase'. So, the question you originally pose, is not applicable, as to phase-angles, and single-phase motors or equipment being designed as such.
A single phase motor will run correctly if it is presented with two wires having the correct voltage and Hz across them. It'd be irrelevant if it comes form a single phase generator or a three-phase one, or even from a 6-phase generator. There are generators of more than 3-phase power, by the way.
One low-voltage scheme may be 120/208 volts in the US. So, as can be seen, 208 may be a little low. However, most of the transformers for such uses have taps, tipically to adjust up or down 5%. So do most welding machines, to account for slight differences in supply voltage, when there's no accesss to transformers taps. Utilities can go and adjust taps, though, if possible. Be aware that voltages vary slightly up/down at different hours and seasons.
For running single-phase machines or equipment, it's a matter mainly of measuring the voltage across those two wires and see that it is not above or below the equipment limits.
Other than that, the loads ought to be balanced to the 3 phase supply, as already mentioned. That means all 3 legs are used by different loads as proportionally as possible. That's an engineer's or electrician's job.
Best wishes.
The electrical service in your home is single phase. When you connect your dryer or oven to 220V, it's 220V single phase. The phase relationship between the two legs is no big deal when the voltage is powering a heating element, but a motor is different.
Single phase motors contain multiple winding to power the motor. To establish a difference in the magnetic polarity between the windings, the single phase is shifted within the motor. A ninety degree phase shift, designed into the motor, provides optimum torque.
Two phase power from a three phase source introduces a 60 degree offset in the power source to the motor. The offset is passed on to the windings. A loss of torque is the result.
Paul
Dear friend,
Phase angle is just what the term describes: An angle difference between two phases. In single-phase voltage there can not be and there isn't any difference in phase voltage.
Single-phase voltage, as we use in our homes from the utilities, comes from a 3-phase distribution system. All single-phase motors throughout the nation are hooked, in escence, to a 3-phase distributionh system, except those hooked temporarily to small portable generators.. A typical home is fed only one of those 3 phases, other homes in the neighborhood are given the other phases to balance the system out.
A single phase motor has winding within itself designed to produce torques by means of internal voltage-current displacements in them. The internal voltages-currents inside the motor will be RELATIVELY displaced from the supply voltage. So the magnitude of the torques produced will be the same for a given measure of voltage supplied.
If you had a balanced 3-phase power supply that matches a single-phase motor, the motor will run the same, no matter from which of those phases it is run from. So, if your home is fed from say phase-A of the nearby transformer, and your front neighbor's home is fed from its phase-B, a given motor will run the same in either home, provided they see the same magnitude of voltage, even though phase-A and phase-B are displaced from each other by 120 electrical degrees.
If this is still not clear, you might want to check with an electrical engineer in your area, or with the utility company.
Edited 4/15/2004 3:38 am ET by mbl
I'm afraid, mbl, that your understanding of electrical distribution systems is limited. Single-phase power in NOT just one leg of a 3-phase feed. The 480v (or higher) 3-phase distribution line powers a delta-configuration primary pole transformer and the complex-connected secondaries of that step-down transformer are what feed the 1-phase drops to the homes/businesses. What we call "240v 1-phase" drops are actually 2-phase, 120v hots, 180 degrees from each other with respect to a neutral, and not the 120 degrees with no neutral that you would get from 2-hots of a 3-phase high line,
A 3-phase drop is normally 208v, leg to leg, but industrial customers can also get 480v 3-phase.
--Lee in Cave Junction, Oregon;
Gateway to the Oregon Caves
Edited 4/15/2004 4:26 am ET by Lee Eschen
Edited 4/15/2004 4:42 am ET by Lee Eschen
Dear Lee,
Single-phase is a term meaning that there are two electrical connection points for single-phase loads, which have two electrical points for feeding them. The neutral does not count as one phase, nor does the ground.
When you have two voltages opposed to each other at 180 degrees, you in essence have zero degrees of difference from one extreme to the other. That does not mean that there is no potential difference, though. Only that it is the same phase.
Best wishes.
mbl wrote: "Single-phase is a term meaning that there are two electrical connection points for single-phase loads, which have two electrical points for feeding them. The neutral does not count as one phase, nor does the ground."
I did not say that neutral or ground counts as a phase. I did say that "240v, 1-phase" actually has 2 hots 180 degrees out of phase. We call it 1-phase, but it is actually 2-phase. Please do not put words into my mouth. OTOH, "120v, 1-phase" is truly 1-phase with the return thru the neutral.
mbl wrote: "When you have two voltages opposed to each other at 180 degrees, you in essence have zero degrees of difference ...."
180 degrees does NOT mean "in phase" but means rather 180 degrees out of phase, just like it says.
--
Lee in Cave Junction, Oregon;
Gateway to the Oregon Caves
Dear Lee,
Since explaining the issue in the least technical way is not effective, will just mention that industrial and commercial plants and sites served by a 3-phase supply are just fed that. They are not fed a separate single-phase service for single-phase loads.
Running low-voltage single-phase motors in those plants and sites has properly been done for ages and will continue to be done so. Those places are strictly inspected and required to meet electrical codes and standards, it ought to be realized.
Will hereby decline to discuss this issue any further, and it is not for lack of knowledge, experience, or professional qualifications.
Best wishes.
Dear mbl,
I owe you an apology, my (I hope) friend. After doing some reasearch on the web and in other forums and reading your two posts, #27 & 31, I realize that my considerable time away from the subject has muddled my thinking. Your explanations are right and mine are, well, somewhat less than correct. My apologies to all and I will try to remember this lesson in all my future posts.
I thank you for your time and willingness to help, even in the face of my ignorance. I hope we can go on from here as friends and partners in learning woodworking and all its related subjects.
Best Regards,
Lee
Edited 4/17/2004 6:26 pm ET by Lee Eschen
Edited 4/17/2004 7:03 pm ET by Lee Eschen
Good Evening Everyone,
Been a beautiful day/night here in Baltimore and just got home to see how
this discussion has been going.
Mbl, I'm really happy that you stayed here and continued sharing your expertise through some confusing messages while everyone worked through this problem.
I never thought I would open such a can of worms!
Lee, I also thank you for your thoughtfulness and for pursuing this issue on
an electrical engineers forum as well.
Paul and others have been great as well.
This reminds how lucky we are to have this way of sharing information
across an entire nation with such speed.
Again, I think this issue is out there for a lot of woodworkers and this thread will serve as a good resource in the archives for others who want to learn about this issue.
Hope you all have a great and relaxing Sunday,
Tom
Dear Iron Dog,
You have kind words and they are appreciated.
-mbl-
Dear Lee,
Thanks for what you say. Please be at peace.
For all of us, sincerity may at times be clouded by our own thinking, yet it never ceases to be there. It's just a matter of looking well, with the right effort.
Resentments are one such type of cloud and are the worst of false values. So, let's none of us treasure such things and just let them go,
But let's keep the good wood-working going! For clouds of dust we are lucky to have real masks.
Best wishes.
-mbl-
Dear mbl,
Thanks, mbl (darn, I wish I knew your real name), for your gracious words.
Best Regards,
Lee--
Lee in Cave Junction, Oregon;
Gateway to the Oregon Caves
Edited 4/18/2004 3:01 am ET by Lee Eschen
Edited 4/18/2004 3:02 am ET by Lee Eschen
A quick note about running 220 volts motors on 208 volt serices.
Yes, the motor should be built with a 10% tolerance in there. So a 220V motor should run fine on anything from 198V to 242V. Just remember, there's also a 10% variation for commercial customers (at least in Illinois) in what the utility can supply to you. So that 220V service could be anywhere from 187V to 229V. This could cause a problem if your voltage is on the lower end of that range.
When people 100 years from now see my work, they'll know I cared. --Matt Mulka
Hi Everyone,
Well we are up to 40 messages now and have worked through some issues and had quite a debate.
I, for one, am not quite sure we have reached a consensus on the original question, which I will restate here with some new wording.
Is it acceptable to use 2 matched legs of a 3 phase supply to power a single phase 220 volt motor?
Certainly the 220 volt motor will run off 2 legs of a 3 phase supply.
But, will this affect the motor adversely over time?
Will it reduce torque?
Are there any other affects it will have?
Again, I thank everyone in advance for your thoughts and patience!
Tom
Yes.
Agreed.
No.
No.
No.
Like I said before there are billions of small (5 hp*) 1 ph motors running on 2 legs of a 3 ph supply with no apparent ill effect. Any perceived damage or degradation is, if not theoretical, is so esoteric to have absolutely no real world effect. If there was a real problem with the motor the waranty would prohibit the application. Likewise if it caused a problem with the serving system then the NEC or the utilities would not allow it either. K.I.S.S.
* Industry norms are to go to 3 ph, 480V above 5 hp to save to reduce the amperage and reduce the amount of copper required to feed and switch that current. Above 200 hp you go to 2300V or 4160V for the same reasons. Insualting for th higher voltage is cheaper than the copper to carry the amps.
John O'Connell - JKO Handcrafted Woodworking
Life is tough. It's tougher if you're stupid - John Wayne
Edited 4/20/2004 7:06 pm ET by ELCOHOLIC
mbl,
I read your reply (to me) carefully and agree with everything you said about single phase.
But the point I was originally making is that a 220/240 volt, single phase motor, is supplied by power from a single phase, not two. Both hot leads come off the same line, whether it's A, B, or C; but not A&B, or A&C, or B&C. The motor itself offsets the phase relationship between windings to develop optimum starting torque. Introducing a phase shift by supplying power from two legs of a three phase system will affect the designed phase offset.
The original question is (in my words) "is it okay to use 2 phases in a single phase motor?"
Paul
>Both hot leads come off the same line, whether it's A, B, or C; but not A&B, or A&C, >or B&C.
Paul, If I am reading what you posted correctly, what you are saying isn't correct as far as my experience goes, and I've wired several plants and a lot of machines.
With Delta configured 240V 3 phase, you have two hot wires, Red and Black, or A and B, plus a current-carrying neutral wire, white , or c. You can connect ANY two wires to run a single phase 240V motor, at least I did for years with a 1000 amp service and lots of machines of varying sizes.
With star configuration, you have 3 hot wires, a, b, and c, plus a neutral. You can connect ANY two hot wires to run a single phase, 240V motor. You can also connect any hot wire plus the neutral wire to get 108 volts, if memory serves (we don't have that configuation around here, so I'm relying on memory).
The green ground wire in both configurationcrries no current except in the case of a malfunction.
This isn't theory, it's actual practice, just like so much of your good finishing advice. If I've misunderstood what you wrote, please set me straight. If pressed, I can diagam how the phase relationships make this possible, but I think the practical reality is enough on a forum like this.
By the way, the plants I ran and my current shop all have both Delta three phase for the machinery plus normal 240 / 120 single phase for the office and for electric hand tools, coffee and vending machines, etc. I suppose you could use a transformer off the three phase installation to get 120, but that isn't the usual practice around here.
Michael R.
Michael,
I finally realized that connecting both supply lines to the same leg of the electrical distribution would not develop a difference of potential (no voltage). No voltage means no current which means no power. Thanks for helping to set me straight; your memory is a lot better than mine.
Paul
Dear Paul,
Will offer this, inspite of having positioned not to discuss further, since you are sincerely asking for help in understanding:
An electrical connection-point of a distribution system IS NOT THE SAME as a 'phase'and that confussion must not persist. It takes TWO (2) connection points to define a phase. There can be more than two connection points in the same phase, and those added points do not increase the number of phases.
Say you have a 3-phase system with points 1, 2, and 3 and no neutral, point 1 IS NOT TRULY phase-A, although it might be CALLED so. The connection *from point 1 to point 2* IS phase-A. Phase B is not point 2 either, but the connection between points 2 and 3 is. Phase C is the connection from point 3 back to point 1.
'Single-phase', for all practicall purposes of connecting a single-phase load, would be ANY 2-connection points in any system, except system- ground.
If a system has a neutral, or if the system has a grounded point, it is irrelevant for a single-phase motor load. The neutral can be ONE connecting point of a phase, but, as said before, no single point counts as a phase.
A single-phase load (including single-phase motors) can be connected to any two electrical points that are voltage-wise adequate for it, other than system-ground. Single-phase motors are specified for a rated voltage and frequency, NEVER for working on any specific phase angle or specific type of system configuration, or generation schemes.
Any concern having to do with other 'legs', 'phases', or 'phase-angles' to which the single-phase motor IS NOT connected ARE NOT valid, as long as that motor sees its rated voltage and frequency at its terminals.
Electrical angles between coils INSIDE of the motor are INTERNAL to the motor which will use the supply voltage as its REFERENCE. The motor has no choice but to follow that reference, and so any measurements taken inside of the motor HAVE TO BE and will always be RELATIVE to the voltage supplied.
TWO (2) electrical points resulting in a potential difference can well be the result of one or VARIOUS coils from a transformer or from one or more generators, each of those coils having whatever phase-angle displacements internally in themselves, and among themselves.
But once you are dealing with only two (2) of those electrical points, it is only the potential difference that matters to a single-phase load because the current at the load will be determined by its impedance and the load will be IN-PHASE with those two (2) electrical points. They have to be, because THEY ARE CONNECTED TOGETHER.
It is as if a person jumps into a running train: as soon as they are together, person and train are IN-PHASE. The person's internal organs keep moving at the usual speeds and displacements RELATIVE to its body, but in truth they might be moving at 80 miles per hour and covering huge distances, making multitudes of turns, and ups and downs, as determined by the tracks.
With motors and their supplies, it is much more straight-forward than with this train-person allegory, though. But just as one can jump into a running train but not jump into a flying plane, a motor can not just be connected onto an excessive voltage or the wrong frequency, else it could be damaged.
By the way, for 3 phase motors and how they connect, the same fundamental principles apply. That is why a 3-phase motor can be connected to a delta, open delta, Y (or 'star', or 'Pi') system, whether grounded or ungrounded, with or without neutral as long as the motor specs are met. Those specs, also, NEVER call for particular system configurations.
And, also by the way, depending on how transformers are connected THEY DO SHIFT phase angles from primary to secondary. But it is not the transformer that shifts the angles, it is HOW they are connected and work together. Yet so, 3-phase motors do not care about those phase-shifts, other than during electrical faults. But that's a separate issue.
As to TWO (2) 180-degree angle differnces in a single mid-point coil of a transformer, it needs to be pointed out that 180 degrees plus 180 degrees totals 360 degrees and it is the SAME as 0 (zero) degrees. So whether the two phasors are added or substracted (180 - 180 = zero, too) it'd make no difference, for in fact they are the same phase. There is really no phase-angle difference there.
Really, the initial concern ought to be dropped.
Best wishes.
mbl,
That's a ton of information you provided and it took me a few minutes to work my way through it.
Let me start by saying that you are correct in your explanations and I have been wrong. One of my pet peeves on various forums is people that have better writing skills than subject knowledge; and now I've done the same thing myself. I apologize for speaking before checking the facts. Oddly, I still remember how to do vectorial sums for voltage, current, power and impedance in series and parallel circuits but have forgotten some of the essential basics (like there has to be a difference in potential to develop voltage).
So the answer to the original question, "is it okay to use 2 phases in a single phase motor?" is YES. It's not only okay, it's necessary.
A point that may need to be addressed is the voltage supplied by the three phase system; it's either 220/240V or 208V (delta or wye). If the motor is rated for 220/240, and the supply is 208V, is there a concern with the power?
Paul
If the motor is rated for 220/240, and the supply is 208V, is there a concern with the power? -Paul-
...
Dear Paul,
Although the motor nameplate may say 240 volts, and X number of amps and HP's, those are NOMINAL ratings, specially for smaller motors.
The actual NEMA (National Electrical Manufacturers Association) and ANSI (American National tandards Institute) design and test voltage for such motors would be 230 volts and 115 volts for such low voltage single phase motors.
So, if there's really 208 volts applied it'd be only a 10% undervoltage being applied which would not be serious. NOMINAL means "by-name or legend" and implies that there is already margin in the unit as built.
NOMINAL also would account for the fact that supply voltages do not stay constant during the day, nor during seasons, nor are ambient temperature conditions the same for all geographical locations and seasons, plus the fact that most motors are (in general) not used at their full rated capacity (it would not be a good application) and many are not run on continuous duty, even.
Very large industrial motors and transformers (industry-level and above) are not considered stock-items and they do not go by nameplate rating (although they'd have one) but rather they go by ACTUAL factory-test reports and/or certificates showing that they actually meet or exceed engineering specifications that include ambient temperature and specific voltage and current measurements, plus other electrical values. When such a unit results to be somewhat lower than specified, it might still be acceptable under the compensation by some monetary deduction, or other arrangements, agreed-upon by the end-user and engineer(s). When the unit exceeds specs, it's to the end-user's free benefit and happiness, though.
Single-phase motors, in an industrial environment are considered much as SECONDARY-level loads. That means that they do not even merit specific detailed engineering designs as to how and where they be connected, but generic outlets are designed and provided-for and they use STOCK local-starters or contactors with protection only for over-load but not for short-circuit conditions. They rely on shor-circuit protection provided by the feeders to those outlets. This is in further support to the explanation that single-phase motors do not care but about what actually touches them. Paradoxically, non-motor single-phase loads such as lighting loads DO require detailed engineering design because their initial investment and operating costs are significant.
Three-phase motors, on the other hand, are controlled and protected from customized motor-control-centers (many motors controlled from one enclosure with solid-copper or aluminum bus-bars) and very detailed engineering is provided relating their feeding, control, and protection. Engineering also includes actual testing of those custom units to match designs, leaving no accountables to chance.
In those centers, in addition to the starter, an electro-magnetic circuit-breaker (or more cheaply fuses) is provided which serves as a diconnect AND as detailed short-circuit protection for the feeders to the motor. That's for low-voltage (3-phase) motors. For 'high-voltage'motors, all of which are 3-phase, much more powerful schemes are used. . For single-phase motors, all of which are low-voltage, a properly rated wall plug is a code-acceptable disconnect. Low-voltage is any voltage below 600 volts in the USA
It is good that you are satisfied and happy. Being able to help is a reciprocal happiness.
Best wishes and good-will to all.
-mbl-
Good explaination mlb.
Before my woodworking days I made high power battery chargers for golf carts. Used old WWII aircraft engine starters purchased at the local surplus yard for $100 each. They had 3 large 220V transformers that I hooked in a Y-D configuration. Y for the primary and D for the secondary. The secondary windings were solid copper about 3/8" od. The secondary windings were connected to six 150 amp diodes that accomplished 3 phase full wave rectification. The primary taps on the transformers were hooked to the center of the Y and gave voltages at the secondary coils that could be varied from about 30 volts to 40 volts.
Anyway, the units had 120V motors running the cooling fans. I simply connected from one leg of the Y to the other then through a step down transformer to get the 120. Most of these units ran continuously for 10 years with no problems.
Once dropped a crescent wrench across the output terminals of the DC while a unit was running. Once my eyesight returned to normal I discovered my wrench was mostly melted!
These units had a switching panel on top with 10 circuits for charging 10 carts at the same time. Was a thriving business until the cart manufacturers started supplying individual chargers with each cart and not getting the charger was not an option. When they did this, they raised the price of the carts $300. Alltogether I made and sold about 50 of these units at $1200 apiece.
PlaneWood by Mike_in_Katy (maker of fine sawdust!)PlaneWood
Dear Mike,
Good wise move to use (re-cycle) those items.
In relation to your account, will say, as you well know, that a battery charger is pretty much the same as a welding machine: Very high-ratio of turns from primary to secondary so as to get a very low secondary voltage. The charger, of course always uses rectifiers. Some weld-units do, some don't.
But one similarity in common is that they can pretty much be short-circuited at the low-voltage end, specially the welders. The chargers not as much due to the rectifiers. Yet, they do put there current-limiting resistors, or the coils of those transormers are special and have high hysteresis that allows saturation which increases the self-impedance upon current flow on them to tolerate shorted ends, since it is quite predictable that the terminals will contact each other occassionaly. That'd be why your charger acted as a 'welding machine' and fused the wrench.
So a tip might be, if you still have those good units, you could certainly re-re-cycle them into excellent welding machines.
Have a good day.
-mbl-
Edited 4/17/2004 3:23 pm ET by mbl
Yeah, those transformers wouldn't saturate enough to make a typical welding machine. Maybe if using 1/4" rods on battleship plating! Most ac/dc welders have a relatively high voltage till the arc is struck then the voltage goes way down. You can do this with a regular transformer by sawing a slot in the iron core plates.
I got out of that business back in 1970 or therebouts. After that I started making 'gas' guages for golf carts. Basically an ampmeter relabeled to read volts and a resistor bridge shaded with a zener diode. Sold several thousand of those at $30 a pop. Tried to get a patent but was to much hassle.
When that latter endeavour ended, I found a heck of a good deal on 10,000 bf of mixed hardwood lumber. Been f-artin around with wood ever since.
PlaneWood by Mike_in_Katy (maker of fine sawdust!)PlaneWood
The original question is (in my words) "is it okay to use 2 phases in a single phase motor?" -Paul-
...
Sorry, "YES".
But keep in mind that TWO electrical connection points constitue ONE phase, not two PHASES.
-mbl-
Having worked with electricity and electronics since I was 11 years old, and having a degree in electronics engineering, and having worked with power control circuits for many years, I was reading this thread and becoming more and more horrified at the misinformation I was reading. Then, finally! Thank you, Paul, for jumping in and clarifying for the folks the difference between single- and three-phase circuits.
Unfortunately, most folks really do believe that 240v single-phase is just two hots from the three-phase branch circuit, when the reality is that those transformers you see hanging on the power poles have the job of changing 480v (or higher) three-phase into 240v single phase for residential drop use.
Anybody interested in a deeper understanding of the relationships between 1- and 3-phase power will be rewarded by a visit to this URL: http://www.sea.siemens.com/step/templates/lesson.mason?bep:2:1:6 (roll your mouse over the picture to see the voltage/phase relationships of 3-phase to 1-phase conversion)
and this one for more info:
http://www.allaboutcircuits.com/vol_2/chpt_10/1.html
I highly recommend reading the facts rather than continuing to spread misinformation around the woodworking community.
--
Lee in Cave Junction, Oregon;
Gateway to the Oregon Caves
Edited 4/15/2004 4:24 am ET by Lee Eschen
Lee,
Like you, I got into electronics at an early age thanks to a neighbor that was an avid ham operator. I spent about ten years in the Navy as an electronics tech and pursued an engineering degree for a couple years before deciding it wasn't the right direction for me. As the years have passed, I've forgotten more than I remember, so I was hestitant to say too much and add more misinformation to the post. I'm glad you jumped in.
Now, it's back to the section of the forum where I'm more up to date....Paul
Hello all,
I have been enjoying reading the posts and think it is very valuable for what we are learning for the first time or correcting our mis-conceptions.
Lee would you not recommend using 2 legs of a 3 phase supply for a 220v single phase motor? As Paul was pointing out there is a concern about the
cycles of the supply not being right for the motor.
My friends machines seem fine running of the 2 legs of the 3 phase (except for the welder ) but the concern is will it be damaging in the longterm.
Regards,
Tom
Hi Tom,
I would definately NOT recommend feeding a 1-phase motor with 2 legs of a 3-phase circuit. There are transformers available to change it to a proper 1-phase/2-phase circuit: http://www.romacsupply.com/catalog/pl15103.html
There are other manufacturers and dealers. Try Google "three phase power transformers".
--
Lee in Cave Junction, Oregon;
Gateway to the Oregon Caves
Edited 4/15/2004 6:15 pm ET by Lee Eschen
Hello Lee,
Thank you for your response to my question.
But, in order for my education to continue, could you
tell me why you don't recommend it?
I have been working my way through the links you posted, particularly
the Siemens link and am enjoying it.
Thanks again for sharing your knowledge,
Tom
This thread has taken a horribly twisted and circuitous (sorry) turn for the worse.
Single phase motors are not 2 phase motors regardless of the voltage or if you have 1 hot and a neutral or 2 hots. Say it with me “Single phase is not 2 phase”.
Single phase motors are not really stupid. They don’t know which way to spin and will spin the same direction regardless of the connection polarity. Since they see only a SINGLE PHASE they have no idea or sensitivity to phase angle rotation.
Poly phase motors use all the available phases and rotate the same direction as the phase rotation of the system. That’s why all you have to do to change rotation is swap 2 of the 3 wires. 3 ph motors don’t really know which way to spin, they just follow.
Transformers are not phase converters, they change voltage, period. Nobody in their right mind installs transformers to run single phase load from a three phase system at the same voltage because it’s a bad idea. If that were so, we’d all have to have 3 ph in our homes and all motors would be 3 phase since almost all commercially generated power is 3 phase.
As I said in my previous post, it’s important to balance the 1 ph load connected to a 3 ph system.
You can run a single phase motor off a three phase system. There's billions of them happily spinning as we speak. The reverse is true, but you probably can’t start it. It’s a bad idea anyway. If a 3 ph motor loses 1 of it’s phases it keeps running but usually overloads the other 2 winding sets. When this happens it’s called “Single Phasing” (there's that phrase again). I’ve engineered oil production applications with isolation transformers on 200 hp and larger submersible pumps to allow motors to single phase and keep running to destruction without effecting the system because maintaining the production process is worth way more than the motor. Many fire water pumps are set-up the same way for obvious reasons.
2 phase motors are getting pretty rare, actually need 2 phases (hence the name), and come in 3 wire or 4 wire configurations. If you have a piece of vintage machinery it may just have a 2 ph motor because they used in most frequently in manufacturing.
OK, about that welder complaining of low voltage. Is it a 3 or 1 phase? It's probably 1 ph unless it's a great big one. Whether your buddy has 208V or 240V shouldn't matter. The nominal rating for such things is 230V and NEMA standards require equipment to operate within +/- 10% of the nominal voltage. Somethings else is wrong, it's probably the way it's wired. On the other hand if this is happening when his machinery is running and he hasn't balanced his load he might actually have low voltage.
John O'Connell - JKO Handcrafted Woodworking
Life is tough. It's tougher if you're stupid - John Wayne
Edited 4/16/2004 8:54 am ET by ELCOHOLIC
I agree with what you posted. One of the plants Iset up had 3 phase bus ducts, and all machinery was hooked to it, from the 75 HP 3 phase dust collector motor on down to the 2 HP single phase bandsaws. The wiring was Delta, with two hot leads and a neutral, plus a ground. The voltage between any two of the current carrying conductors was 220 volts. Obviously, you couldn't split any of the 220V pairs so we had to use transformers to get 120V or 24V for control circuits.
Star systems will work the same way, except all three wires are hot, with equal voltage between each one (due to phase angle.)
Michael R.
Hi Paul,
Yes, I too was pulled in by a local ham, Bob Street, W6PDD, an engineer at Pacific Bell, and now an SK. Bob also influenced my friend and classmate, Francis (Laddie) Smith, W6WIV, with whom I have since lost contact. I heard that he became an MD.
I got my Novice (WV6AEG) at age 11 and my Tech (WA6AEG) ticket at 12. A later upgrade changed my call to N6AXB which I still hold as an Extra at 59. My wife, Mary Catherine, is also licensed, KK6NC.
--
Lee in Cave Junction, Oregon;
Gateway to the Oregon Caves
Edited 4/15/2004 6:12 pm ET by Lee Eschen
Tom,
I would be concerned about using two phases with a single phase motor. Single phase motors have various design schemes built in to shift the single phase bewteen the windings to develop torque and turn the motor. By introducing a 60 degree phase shift in the supply, you'd be counteracting the design.
The most obvious effect would be a loss of torque during start-up.
Paul
My Website
This forum post is now archived. Commenting has been disabled