Document 34: The History of the Induction Motor in America

Note to reader: As a "document" on my website, this webpage varies from the "normal". By normal I usually mean a text that, in one way or another, relates to the broad area of woodworking history. Typically, the pages designated "DOCUMENT" feature ONE document and some introductory descriptions designed to set the document into an historical context. As you scroll down on this page you will notice selections from a wide range of books and other sources that, in one way or another, give details about the tortuous but fascinating emergence of the fractional horse-power motor, one of man's truly "revolutionary" inventions. Revolutionary in the sense it, the fractional hp motor, liberated us from the tedium of hand and/or foot power for certain operations in woodworking.

And, yes, this page is rather long. Be prepared for perhaps more info that you bargained for; regardless, the story of the fractional hp electric motor is read at the same both fascinating and worthwhile.

What is not readily understood, however, that simply the concept of "one motor to power each woodworking machine" was, in itself, a "revolution". To prove this point for yourself, scroll down to the image from the Delta manual (below), published in the early, early '30s, that shows the following set up: one 1/3-hp motor driving with a line-shaft, four or five scaled-down machines: e.g., table saw, lathe, bandsaw, jig saw, and horizontal mortiser. True, this same manual also shows the ideal, i.e., one motor for each machine, but discerning readers will note that the passing from the '20s to the '30s, even with "The Great Depression" creating its effect, was a period full of major changes in how woodworking was conducted in home shops. For more, on this, read here.

More than any other factor, the fractional-horsepower electric motor generated an enthusiasm for woodworking as a leisure-time activity by amateurs. Fractional horse-power motors, themselves, would not have been developed without the push toward urban -- and later rural -- electrification, using alternating current. 

Electrification began in the cites around 1915. With electrification, the potential market for clothes washing machines, refrigerators, vacuum cleaners, and a host of related appliances, was recognized by major manufacturers -- like Westinghouse and General Electric -- who already were in the business of selling large motors of industrial settings. By 1920, over 500,000 fractional horse-power motors were powering clothes washers and other appliances in America. 

For amateur woodworking, progress occurred as a series of stages: -- rather than foot-power -- it was a major gain,

first, to get an electrical power source  to drive major tools, like tablesaws, bandsaws, lathes, i.e., direct drive electric motors (before 1915),

second, to move to motors powered by alternatinging current, but

third, where a line of machine tools were driven by a single motor, using shafts and pulleys -- see illustration from Delta's set-up below --, and

finally, to where each tool had its own motor.
(See Warren D. Devine, "From  Shafts to Wires: Historical Perspective on Electrification", The Journal of  Economic History, Vol. 43, No. 2 (Jun., 1983), pages 347-372.

There seems not be an equivalent article that covers American society in a focus similar to G Leslie Oliver, "Fractional Horse Power Motor and Its Impact on Canadian Society and Culture," Material History Review 43 spring 1996, pages: 55-67. Oliver's point: much less evident in the literature are the results of research into the implications of specific, small and unobtrusive technologies, especially those that enter the home (often by the back door). Oliver argues that the appearance fractional horse power electric motor set in motion a series of changes in living that had a major impact upon behavior, values, and the like, but these shifts occurred without much awareness.Further, Oliver adds,

There is little to help us to understand better what the[se technologies] are, what they do, how they work and their intended, unintended, as well as their unanticipated and unplanned for consequences - those now increasingly evident as the twentieth century draws to a close.

Beginning around 1920, the application of fractional horsepower motors was no longer confined to the driving of electric fans or to the operation of toys. (Document 30: George A Schock: Early History of the Baldor Electric Co., 1920-1976 1992.)

According to the electrical engineer, Edward L Owen,

The induction motor enables us to refrigerate our food, climatize our living space, and perform many other tasks that we take for granted.

True, the development of these smaller motors was partly stimulated by the growing popularity of the individual-drive systems in small workshops -- which replaced the shaft-drive system (below, see Delta recommended set-up in the Motor Driven Shop, 1930)  --  copied from nineteenth century industrial applications -- and the growing availability of portable electric tools, especially the introduction of greater torque capability.

delta shaft drive 1930

However, the real driver for developing a market for these motors was their  application in domestic settings. It was the housewife demanding  motor-driven washing machines, ironing machines, vacuum cleaners, dish-washing machines, sewing machines, refrigerators, piano players, and a host of similar appliances, for which motors are required.

Examples: Important in this advance in technology  was the development of capacitor motors in 1925. [need sentence noting what the significance of this innovation was] Electric motors, which are, basically, copper wire wound around a magnet, are either multi-phase or single-phase.  Multi-phase motors, on the one hand, generate starting torque along the various windings by applying out of phase voltages to each winding in a pattern that generates a torque force in the desired direction.  Single-phase motors, on the other hand, must generate the same starting torque. However, because  they have only one phase to work from, single phase motors need the  means generate and send a shifted version of the single phase voltage to one of their windings.

There are three common methods of creating single-phase electric motors:  (1) capacitor start, (2) split-phase, and (3) shaded pole.  Each other these motors has some method to provide starting torque to the motor by shifting the voltage given to one of the windings on the motor by some angle.  This phase shift corresponds to one winding of the motor having a voltage before another coil.  The difference in time between when one coil has a voltage and when a second coil has a voltage causes the torque force and begins the movement of the motor.

In short, and  without  getting unnecessarily more technical,  the capacitor provides a delay in the energy given to one of the windings.  This delay causes the forces of the motor to be unbalanced and the motor then starts.

Economically, capacitor start motors are often more costly due to the inclusion of the capacitor however they have the most starting torque This means that you probably have one in your refridgerator, washer, dryer, or other application, like woodworking tools,  where you may need a lot of starting force but you won't find them in your electric fan.

Improved Construction Features

Because they replaced steam engine drive with long shafts and belts. early motors featured sleeve bearings in pillow blocks. As a result, these motors could only be horizontally mounted and used indoors, in dry atmo­spheres. Any exposed electrical parts also made them unsafe. Later [when?] end brackets, with sleeve bearings and double-end ventilation,  were adopted, making these motors both safer and widened the range of application, including to amateur woodworking settings. However, it was the development of totally enclosed motors with fan cooling which en­abled these motors to be used outdoors, in say, uninsulatd garages, or even outdoors. For a very good example of an electric motor operating outdoors, see article by J R Koontz, “Driving the Farm Pump Electrically,” Shop Notes v 21 (1925), pp 1-2.

E T Painton's "Preface"

to his Small Electric Motors DC and AC London: Pitman, 1923

THE application of fractional horse-power motors is no longer confined to the driving of electric fans or to the operation of toys. The growing popularity of the individual drive system in small workshops, and the increasing use of portable electric tools, has stimulated development of motors, which, though of very small size, are of excellent electrical and mechanical design, and form miniature power units of great reliability and good performance. An even more modern application is found in the domestic sphere, where there is a steadily increasing demand for motor-driven washing machines, ironing machines, vacuum cleaners, dish-washing machines, sewing machines, refrigerators, piano players, and a host of similar appliances, for which motors are required, sufficiently robust to withstand rough handling by a non-technical user, but at the same time light in weight and capable of enduring severe service conditions.

Motors for such purposes operate upon the same principles as larger machines, but their operating characteristics often differ widely, and it is the object of this book to indicate the general characteristics of small motors, pointing out departures from the well-known characteristics of large machines, and setting out the general principles governing their performance.

For this reason some importance is placed on test results obtained in typical small motors, and at the same time considerable space, in illustration and text, is devoted to the constructional features of motors of various types. ...

For an account of the fascinating history of the induction motor, see

Herbert Vickers, Induction Motor: The Theory, Design, And Application Of Alternating-Current Machines Including Fractional HP Motors Second Edition London: Longman & Sons, 1958


The discovery by Gambey, the instrument-maker of Paris, that a compass needle, when disturbed and set oscillating, comes to rest more quickly when it is in the vicinity of copper, than when wood is near it, was made in 1824. At that time also Barlow and Marsh, at Woolwich, had observed the effect on a magnetic needle of rotating it near a sphere of iron. Arago published, in 1824, an account of an experiment with a compass needle within rings of different materials. In this experiment he pushed the needle aside to about 450 and counted the number of oscillations made by the needle before the swing decreased to 0°. With a ring of wood the number of oscilla-tions was 145; with a copper ring 66; and with a stout copper ring only 33.

In 1825 he suspended a compass needle over a rotating copper disc and found that, by turning the disc slowly, the needle is deviated out of the magnetic meridian. By rotating the disc fast enough he found that continuous rotation of the needle could be produced. The brilliant discovery by Faraday, in 1831, of electro-magnetic induction provided the solution to the question of the origin of the forces present in the above experiments of Gambey, Barlow and Marsh, and Arago. Faraday showed that the rotation of the Arago disc was due to induced currents, set up in the disc by relative motion of disc and compass needle.

From 1831 to 1879 this valuable discovery produced no further results.

In June, 1879, Mr. Walter Baily read a paper, before the Physical Society of London, on "A Mode of Producing Arago's Rotations." Baily used a fixed electromagnet with four magnet cores joined to a yoke.

The four magnet cores were about 4 in. long and each was wound with about 150 turns of insulated copper wire of 2.5 mm diameter. The coils were connected two and two in series, similar to two independent horse-shoe magnets and were set diagonally across one to another.

The two circuits were connected separately to a revolving commutator, built up of a simple arrangement of springs and contact strips mounted on a piece of wood, with a wire handle by which it was turned. By rotation, the currents from two batteries were caused to be reversed alternately in the two circuits, and this gave rise to the following changes in polarity of the four poles.

In this rotating magnetic field a copper disc was suspended. He stated : "The rotation of the disc is due to that of the magnetic field in which it is suspended, and we should. expect that, if a similar motion of the field could be produced by any other means the result would be a similar motion of the disc." He also suggested that if a whole circle of poles were arranged under the disc, successively excited in opposite pairs, the series of impulses all tend to make the disc revolve in one direction around the axis, and added:

"In one extreme case, when the number of electromagnets is infinite, we have the case of a uniform rotation of the magnetic field, such as we obtain by rotating permanent magnets."

It is clear that Mr. Baily had grasped the fundamental principle of action of the induction motor, and the motor he exhibited before the Physical Society, in 1879, was the first induction motor, but it needed later important discoveries of methods for producing the revolving field by means of alternating currents to make it the useful machine that it is to-day.

The next discovery was made by Marcel Deprez in 1883.

Deprez fed alternating current to a coil, which produced an alternating or oscillating field along the OX axis. He supplied another coil, whose magnetic axis made an angle of 900 with the OX axis, with alternating current, whose phase difference was 900 in time from the current in the first coil, and showed that a revolving field of constant amplitude could be produced. The frequency of the two currents was the same. He also showed that if the two currents were of equal period, but not of equal amplitude, an elliptically rotating field was produced. The number of turns in each coil was the same.

Professor Ferraris arrived at the same conclusions as Baily and Deprez in 1885, and apparently without knowing of the work of either. His paper on "Electrodynamic Rotations Produced by Means of Alternating Currents" was published in 1888. He sug-gested the method of obtaining currents, differing in phase by nearly 90°, by inserting a resistance in one winding and inductance in the reactance other, thus making the ratio of resistance small in one winding and large in the other. This method, it may be noted, is largely used for starting p single-phase motors.

Then followed the great work of Nikola Tesla between 1887 and 1891. His researches placed the induction motor on a sound founda-tion. His patents were sold to the Westinghouse Co. of America, whose pioneer efforts in this field must be recognized. In that period, however, the only a.c. supply circuits were single phase, and the frequencies were 133 and 125 c/s. These supply circuits were obviously unsuitable for the development of the motor.

In 1891 the Electrotechnical Exhibition at Frankfort was held, and three-phase transmission of power was demonstrated....

However, significantly, right on the cusp of the 1920s (dated 1930, but necessarily written in the late 1920s), is the Tautz and Fruits’ chapter xviii, “Power, current and motors”, subtitled “power to operate woodworking machinery”, in their Delta manual, the 1930 Modern Motor-Driven Woodworking Shop. For a pdf version of the 1st volume of the Modern Motor Driven Woodworking Shop, scroll down to Tautz on this linked page, dedicated to numerous pdfs of vintage woodworking manufacturers' catalogs and woodworker's manuals.

In the box below is the type of headline a prospective woodworker was confronted with in magazines such as Popular Mechanics, Popular Science, and the like in the 1920s


The induction motor drives amateur woodworking! Without the induction motor, only hand tools and/or foot powered tools would be available to the amateur woodworker.

Baldor Motors began manufacturing electric motors in 1920

About 1923, the first woodworking machines were built in small sizes for hobbyists by a company in Milwaukee. Today these small-type machines are manufactured in several sizes in almost unlimited quantities at prices such that many people equip basement shops as a hobby. They have proved so valuable that many manufacturers use them for making small parts.

Following along this development, portable electric-motor­-driven tools for many of the operations formerly performed by hand in the building trades were developed. All of these are equipped with ball bearings, light in weight, and very practical.

List of fractional hp induction motor manufacturers in U.S.

A.O. Smith

531 N. Fourth

Tipp City, OH 45371 Phone: (513) 667-6800 Fax: (513) 667-5873


P.O. Box 2400

Fort Smith, AR 72902 Phone: (501) 646-4711 Fax: (501) 648-5792

Document 30: George A Schock: Early History of the Baldor Electric Co., 1920-1976 1992 


Brook Crompton

3186 Kennicott Ave. Arlington Heights, IL 60004 Phone: (708) 253-5577 Fax: (708) 253-9880



333 Knightsbridge Pky. Lincolnshire, IL 60069 Phone: (800) 323-0620 Phone: (708) 913-8333 Fax: (800) 722-3291



Emerson Electric/U.S. Motors

8100 West Florissant Ave.

P.O. Box 3946

St. Louis, MO 63136 Phone: (314) 553-2000 Fax: (314) 553-1196


General Electric

P.O. Box 2222

Fort Wayne, IN 46801 Phone: (800) 626-2004 Phone: (219) 439-2000 Fax: (219) 439-4644



2100 Washington Ave. Grafton, WI 53024

Phone: (414) 377-8810 Fax: (414) 377-9025


22801 St. Clair Avenue Cleveland, OH 44117-1199 Phone: (216) 481-8100 Fax: (216) 383-4730



1881 Pine Street

St. Louis, MO 63103 Phone: (800) 325-7344 Fax: (800) 468-2045



P.O. Box 8003

Wausau, WI 54402 Phone: (715) 675-3311 Fax: (715) 675-6361



24701 Euclid Ave.

Cleveland, OH 44117 Phone: (800) 245-4501 Phone: (216) 266-7000 Fax: (216) 266-7536



4620 Forest Ave. Norwood, OH 45212 Phone: (513) 841-3100 Fax: (513) 841-3290



16752 Armstrong Ave. Irvine, CA 92714

Phone: (800) 654-6220 Fax: (714) 474-0543



14381 Chambers Rd. Tustin, CA 92680

Phone: (800) 828-8641 Fax: (714) 838-3295



6877 Wynnwood

Houston, TX 77008 Phone: (713) 864-5980 Fax: (713) 864-9502



13131 W. Little York Rd. Houston, TX 77041 Phone: (800) 231-1412 Phone: (713) 466-0277 Fax: (713) 466-8773

Westinghouse Motors

IH-35 Westinghouse Road P.O. Box 277

Round Rock, TX 78680 Phone: (512) 255-4141 Fax: (512) 244-5500

An account of the course of the development of the fractional horse-power motor is given by Philip Alger and Robert Arnold, in

"The History of Induction Motors in America"Proceedings of the IEEE  64 1976, pages 1380-1383. Other  articles that focus on the this same motor are listed below, in the cream-colored box. 

Philip Alger and Robert Arnold

"The History of Induction Motors in America"

Proceedings of the IEEE  64 1976 Pages: 1380-1383.

Abstract: Reviews the history of the induction motor from its invention by Nicola Tesla in 1888 through the various stages of its development:

--the invention of the cast aluminum squirrel-cage winding,

-- improvements in magnetic steel and insulation, and

-- the progressive reduction of the dimensions for a given horsepower rating,

so that today a 100-hp motor has the same mounting dimensions as the 7.5-hp motor of 1897.

Among the first firms to launch a fractional horsepower motor business was Baldor Electric. Beginning in 1920, Baldor -- still in operation today -- is an  event that helped place fractional horse-power electric motors on the mass market and acted as a catalyst for the invention and production of power tools, scaled for the homeworkshop:

From George Schock's "History" of Baldor Electric:

Chapter 1: Baldor's Beginning

Very early in the year of nineteen hundred and twenty (1920) two men conceived the idea of becoming a manufacturer of electric motors.

They were Edwin C. Ballman, a graduate. of Washington University, who graduated with a Bachelor of Science degree and whose major study was electrical engineering; and Mr. Emil Doerr, who had learned the trade of machinist through many years of first hand experience in all phases of metalworking. Mr. Doerr had advanced through all stages of becoming a master machinist, beginning with his apprenticeship. At the time that he co-founded Baldor, he was eminently qualified as a master machinist.

These two men had worked at the same places, Wagner Electric Co. and the St. Louis Electric Co. They did not work closely together in those places, but they were well acquainted and had confidence in each other. Mr. Ballman was experienced in the field of electrical engineering and Mr. Doerr was fully experienced and knowledgeable in electrical manufacturing, including motors; also in supervising and running a metalworking plant. Both were ambitious and hard working and both were honest. Each had respect for the other and they became a team.

In choosing a name for the corporation they agreed to use the first part of the name of one founder (Ball) and the full name of the other (Doerr) (Ball-Doerr). To make the name simpler and more distinctive a new word was coined, hence Ball-Doerr became Baldor. This was a good choice because Baldor is distinctive and rare.      

The original basis for going into the motor business was to "Make a Better Motor". This basis was adhered to strictly, not only at the beginning, but throughout the company's history. In fact, the company's original slogan        

                               -- "Baldor -- a Better Motor" —      

aptly expressed the company's philosophy, then and now... Read More : --

Power woodworking tools, scaled for the homeshop, began to appear in the second decade the 20th century. Introduced in 1914, the 4-inch J D Wallace "portable" jointer was driven by a direct-current motor.

The Building Age 36 December 1914 , pages 84-85

The Wallace Bench Planer

One of the latest candidates for popular favor in the way of a bench planer is the little machine which is being introduced to the attention of carpenters and builders by J. D. Wallace, 527 West Van Buren Street, Chicago, Ill., and shown in operation in Fig. 12.

review of wallace planer 1914This is a portable power planer which weighs only 50 lb. including its direct-connected electric motor. It will be observed that the planer stands on the bench without fastening and can be operated from an electric light socket. It is furnished with either direct or alternating current motor, although if desired it can be arranged for belt drive from a countershaft. It is of such a nature that it can be carried directly to the job and put into operation at a moment's notice.

The planer is said to take the heaviest cuts in hard as well as in soft wood and in addition will take a fine cut that will not show the knife marks. Its fence is adjustable to any angle and the table to any depth of cut.
photo of 1914 wallace portable jointerIts cutting knives are 4 in. wide, but by removing the fence, stockup to 12 in. wide can be roughed off.

The cutter head is cylindrical and the throat opening averages only 1 in. in width—half the usual size. The device is a planer pure and simple, there being no attachments for doing other work. Mr. Wallace, the manufacturer, makes the prediction that before another season is over this bench planer will be considered as necessary to a carpenter and builder as a try square and will eventually eliminate the hand plane from the tool kit.


no 8 wallace portable universal saw

On the left is the 1920s version of the No. 8, J D Wallace "socket-driven" table saw. (The socket-driven set-up reflected early wiring standards.) The 1920s Wallace catalogs also show smaller, "bench top" versions, including a 1/2-HP Direct Drive.  Note, too, the tilting-arbor mechanism.

As time permits, I will continue to add material, manufacturer by manufacturer, about the impact of the fractional horse-power motor on the creation of small scale power woodworking machine tools. This material, generally, will be treated in Chapter 4. Chapter 4, though, -- because it is so full of details I need to convey -- is proving difficult for me to manage in an online setting. As I seek different configurations for the best mode of organization, please be patient.)

Brief Bibliography on the Development of the Induction Motor

Bernard Garver Lamme; "The Story of the Induction Motor", Journal of the American Institute of Electrical Engineers 40 march 1921, pages 203-223

(long account by a pioneer in the development of inductions motors; bio of Bernard Garver Lamme:

Joseph C Michalowicz, "Origin of the Electric Motor", Electrical Engineering 67 1948 pages 1035-1040.

Edward L. Owen, “The induction motor's historical past”, IEEE Potentials 7 (October 1988), pages 27-30.

Kendall J. Dood, Leland I. Anderson, Ronald R. Kline "Tesla and the Induction Motor", Technology and Culture 30, No. 4 October 1989), pages . 1013-1023.

Ronald Kline "Science and Engineering Theory in the Invention and Development of the Induction Motor, 1880-1900", Technology and Culture 28, No. 2 April, 1987, pages 283-313.

Jack Foran The Day They Turned The Falls On: The Invention Of The Universal Electrical Power System

Philip L. Algerand Robert E. Arnold, "The History of Induction Motors in America", Proceedings of the IEEEE 64 No 9 September 1976, page 1380-1383.

Click here to go to the material on the formation of Baldor Motors

Philip Alger and Robert Arnold

"The History of Induction Motors in America"

Proceedings of the IEEE  64 1976 Pages: 1380-1383


INVENTED BY Nikola Tesla in 1888, the alternating-current (ac) induction motor has had a major role in the development of the electrical industry. It is used by the millions to drive the machines of industry and our homes and office appliances. The story  of its evolution, whereby 100-HP motor today occupies the same space as 7.5-HP machine of 1897, is a remarkable example of engineering advancement.


Tesla knew that a piece of metal could be dragged along by drawing a magnet across it, and that a magnetic field could be made to move by building up a current in a coil, as the current in an adjacent coil decayed. That is, by supplying currents out of time phase to successive coils of a motor, the magnetic field would revolve.

Tesla's work led him to apply for patents in October 1887, and a number were granted to him in May 1888. He presented a paper before the American Institute of Electrical Engineers (AIEE) soon afterward, in which he described three forms of his invention. In each, there was a ring-wound stator with 4 salient poles. In the first form, the rotor also had 4 salient poles, forming a reluctance motor that was not self-starting, but would run at synchronous speed. The second form had a wound rotor forming an induction motor, that would start, and run at a little below synchronous speed. The third form was a true synchronous motor, obtained by supplying direct current to the rotor winding.

George Westinghouse at once bought Tesla's patents and employed Tesla to develop them.


Westinghouse assigned C. F. Scott to work with Tesla. They soon substituted a salient-pole stator, with four slot-embedded coils and a small air gap, for the ring-wound stator. Then B. G. Lamme took a hand, changed the design to a two-phase dis­tributed stator winding, and added a distributed rotor winding. In these ways, Westinghouse had achieved a practical induction motor by 1892.

However, the only power then available was single phase of high frequency. To promote a practical polyphase system, Westinghouse exhibited a 300-hp two-phase 220-V induction motor at the Chicago World Fair in 1893, with power-supplied by a pair of single-phase 60 Hz 500-hp alternators on the same engine shaft, but displaced 90°, so that they provided two-phase power. The motor had 12 poles with a distributed two-phase primary winding of cable threaded through partially closed rotor slots. The stationary secondary also had partially closed slots, with one conductor per slot, connected in two secondary circuits 90° apart. In starting, these secondary cir­cuits were closed through a series of long and heavy carbon rods, that were short-circuited when the motor came up to speed. As the carbon rods became red hot in starting, they were placed in the basement so the public would not see them.

In accord with a suggestion from Lamme, Westinghouse then developed a line of 60-Hz polyphase alternators, to supply a line of 60-Hz motors introduced in 1893. These had rotor primary windings, to avoid the difficulty of handling the large secondary currents through slip rings.


In 1891 the Thomson-Houston Company began work on three-phase induction motors under the direction of H. G. Reist and W. J. Foster. These machines had rotating second­aries with iron grids inside the rotor, connected to the rotor windings, and a centrifugal switch for short-circuiting the grids at speed. While many of the early motors were two phase, the more economical three-phase system was soon adopted by both companies. The transition from two-phase to three phase was aided by C. F. Scott's invention of the T connection of two transformers, to provide balanced three-phase power from two-phase systems.

The absence of collector rings gave the GE motor a selling advantage over the Westinghouse motor with its primary wind­ing on the rotor. In response to the problem, B. G. Lamme of Westinghouse devised the bar winding, later called a squirrel cage, and placed this on the rotor. General Electric soon followed suit and, with the signing of a cross-licensing agree­ment in 1896, both companies were free to use the best design, without patent litigation.

C. P. Steinmetz of General Electric, by his many AIEE papers, taught a whole generation of engineers how to deal with ac phenomena. His use of the letter j to represent a 90° rotation, enabled a motor to be represented by its equivalent circuit, as in Fig. 1. Calculations with this circuit were far more convenient than use of the circle diagram that was the basis for the early theory of the induction motor. Steinmetz was truly the patron saint of the GE motor business.


Tesla realized that the magnetic field must move to make the motor rotate, and he invented the split-phase winding to ac­complish this from a single-phase supply. He used two dis­placed windings fed from the same supply, one winding having a much higher resistance than the other, so that the currents were displaced in phase. The motor had good starting torque, but the high-resistance winding had to be opened when the motor approached full speed, to avoid prohibitive losses. The General Electric SA motor, widely used for washing machine drive, was of this type, with the windings on the rotor and a squirrel cage on the stator. The slip rings, brushes, and centrifugal switch were drawbacks, and this type of motor disappeared when capacitor motors came along, in 1925.

At that time reliable low-cost capacitors became available, permitting the use of a series capacitor to supply the phase shift for one of the displaced windings. The current in this winding led that in the main winding by nearly 90°, so that the starting performance was that of a two-phase motor. As the speed rose the phase angle between the two currents de-creased and then reversed, so that the auxiliary winding had to be opened at speed. The motor then operated as a single-phase motor. The capacitor-run motor used a smaller capacitor, giving a lower starting torque, which was still adequate for fans and similar loads.

For loads greater than one horsepower, the Thomson repul­sion motor was widely used before capacitor motors became common. This had a commutator, with the brush axis dis­placed from that of the stator winding. The brushes were short-circuited, so that a high starting torque was produced, and the speed rose until limited by load and losses. A centrifugal switch short-circuited the whole commutator at speed, when the motor ran as a pure single-phase motor. The type went out of use with the arrival of the capacitor motor.


An early problem was that of connecting the rotor bars to the end rings of squirrel-cage motors. Bolts loosened, cor­roded, and overheated at imperfect joints. Spring washers were not effective, and solder melted. Silver brazing and welding were satisfactory but expensive.

In 1916 H. G. Reist and H. Maxwell of GE patented a cast rotor made by pouring molten metal into a mold surrounding the core of an induction motor while it was rotating, and continuing the rotation until the metal congealed. About 1920, H. Maxwell and W. B. Hill of GE developed the art of centrifugal casting of aluminum squirrel cages, so that bars and end rings with fans, were formed in one piece. To do this, the aluminum had to contain a small amount of silicon, and the temperature of the laminations adjusted to avoid breaking the bars when they cooled, after casting.


To reduce the eddy currents in the magnetic material, motors are made of thin steel laminations, cut into desired shapes by steel punches and dies. In the early days common iron 25 to 30 mils (0.063 to 0.075 cm) thick was used, but 14 mils (0.035 cm) was used for large motors. It was found that adding 1 to 3 percent of silicon increased the resistivity of the steel and reduced these losses. Grain-oriented steel is also used today to increase the permeability.


Improvements in insulation were of major importance in the evolution of induction motors, proceeding from a reliance on organic fibers and shellac to use of all synthetic high-temperature resins and glass fiber. The first step was the sub­stitution of enamel for cotton or paper wire covering. This saved space and reduced the temperature drop between the wire and the slot wall. The second step was the development of new and better inorganic insulating materials with much higher temperature endurance, and the third step was the es­tablishment by the IEEE of test procedures calling for func­tional evaluation and classification of insulation systems in accord with their temperature limits, up to 180°C, rather than by chemical composition of the materials.

All components of motor insulation systems have been improved in dielectric strength, moisture absorption, tempera­ture endurance, and bonding strength. One result has been the replacement of the early form wound coils in open slots by random windings in semi-closed slots. This has reduced the magnetizing current, improved the power factor, and lowered the cost. Nowadays, random windings are standard up to motor ratings of 500 hp or more.

With the increased ratings allowed by these improvements, the amount of material per horsepower was reduced, and the rate of temperature rise was much greater when a motor was stalled. On this account, the overload relays were improved, and finally thermotectors or thermistors were embedded in the windings, to react to the actual winding temperature, and give protection against all causes of overheating.


The very early motors had sleeve bearings in pillow blocks, because they replaced steam engine drive with long shafts and belts. Such motors could only be used indoors in dry atmo­spheres, and with horizontal mounting. The exposed electrical parts also made them unsafe. Soon the adoption of end brackets, with sleeve bearings and double-end ventilation, made them safer and widened the range of application. The development of totally enclosed motors with fan cooling en­abled them to be used outdoors and in all kinds of atmospheres.

Gray cast iron has generally been used for medium-sized motor frames because of ease of casting contours, ribs for strength, heat dissipation, low cost and stability of dimensions. For small motors, pressed steel frames with aluminum end shields are widely used. Fabricated steel frames are used for very large motors.


As a result of the improvements in insulation, steel, and de-sign skills, designers have been able to put a great deal more copper in a given slot space, and the temperature difference between the copper and the slot walls has been greatly reduced. Thereby, it has been possible to greatly increase the rating for a given motor frame. The slots have been made narrower and the teeth wider, allowing an increase in the magnetic flux and a decrease in the number of turns per coil for a given voltage. To avoid hot spots in the centers of long cores, radial ducts were introduced, with rotor spacers as fans, that draw air through axial holes in the rotor.

In these ways, the rating assigned to the NEMA frame 404, with a height of shaft above the foot of 25.4 cm (10 in) and a length between foot bolt holes of 31.1 cm (12.25 in) was in-creased in steps from 7.5 hp in 1897 to 100 hp today, as shown in Table I. In recent years designers have optimized designs and conserved materials. Fig. 2 shows how the NEMA frame 404 has visually changed over the years.


[1] N. Tesla, "A new system of alternate current motors and trans-formers," AIEE Trans., vol. 5, pp. 308-324, 1888.

[2] C. P. Steinmetz, "The alternating current induction motor," AIEE Trans., vol. 14, pp. 185-217, 1897.

[3] C. P. Steinmetz, "The single phase induction motor," AIEE Trans., vol. 15, pp. 103-174, 1898.

[4] C. P. Steinmetz,, "Notes on single phase induction motors and the self-starting condenser motor," AIEE Trans., vol. 17, pp. 25-61, 1900.

[5] C. A. Adams, "The design of induction motors," AIEE Trans.. vol. 24, pp. 649-684, 1905.

[6] W. J. Branson, "Single phase induction motors," AIEE Trans., vol. 31, pp. 1749-1787, 1912.

[7] C. P. Steinmetz and B. G. Lamme, "Temperature and electrical insulation," AIEE Trans., vol. 32, pp. 79-88, 1913.

[8] B. G. Lamme, "The technical story of the frequencies," AIEE '          Trans., vol. 37, pp. 65-85, 1918.

[9] B. G. Lamme,, "The story of the induction motor," AIEE Journal, vol. 40, pp. 203-223, 1921.

[10] B. A. Behrend, The Induction Motor, 2nd ed. New York: McGraw-Hill, 1921.

[11] P. L. Alger, "The development of low starting current induction motors," GE Rev., vol. 28, pp. 287-294, 1925.

[12] B. F. Bailey, "The condenser motor," AIEE Trans., vol. 48, pp. 596-606, 1929.

[13 ] W. J. Morrill, "The revolving field theory of the capacitor motor," AIEE Trans., vol. 48, pp. 614-629, 1929.

[14] C. G. Veinott, Fractional Horse Power Electric Motors. New York: McGraw-Hill, 1948.

[15 ] P. L. Alger, "The magnetic noise of polyphase induction motors," AIEE Trans., vol. 73, pp. 118-124, 1954.

[16] P. L. Alger and K. N. Mathes, "Progress in insulation evaluation, life testing methods and standards," Insulation, vol. 1, no. 6, pp. 8-14, Oct. 1955.

[17] P. L. Alger, Induction Machines, 2nd ed. New York: Gordon and Breach, 1970.

[18 ] R. F. Woll, "The integral horsepower ac electric motor," Westinghouse Eng., vol. 31, pp. 120-125, 1971.

Sources: the section draws on Edgar T. Painton Small Electric Motors DC and AC London: Pitman, 1923; Harry Jerome, Mechanization in Industry. NY: National Bureau of Economic Research, 1934, pp 174-175; Herbert Vickers, Induction Motor: The Theory, Design, And Application Of Alternating-Current Machines Including Fractional HP Motors Second Edition London: Longman & Sons, 1958;  Philip Alger and Robert Arnold “History of Induction Motors in America,” Proceedings of the IEEE, V 64: 1976, pages 1380-1383; Warren D. Devine, "From Shafts to Wires: Historical Perspective on Electrification", The Journal of Economic History, Vol. 43, No. 2 (Jun., 1983), pages 347-372; Edward L. Owen,  “The induction Motor's Historical Past”, IEEE Potentials 7 (October 1988), pp. 27-30; G Leslie Oliver, "Fractional Horse Power Motor and Its Impact on Canadian Society and Culture," Material History Review 43 spring 1996 Pages: 55-67.

Also a search of the Reader’s Guide To Periodical Literature (begins 1895), digitized database fails to unearth article of any substance on inductive fractional horse power motors, even though these motors are widely distributed in domestic appliances, such as washers, refrigerators, and the like.

Likewise a search the pages of Popular Mechanic’s Shop Notes, published between 1904 and 1930,  shows only a few article dedicated to electric motors, e.g., the Koontz article cited above.