TECHNICAL

Baldor Basics: Motors

Edward Cowern, P.E.
A continuing series of articles, courtesy of the Baldor Electric Co., dedicated
primarily to motor basics; e.g. — how to specify them; how to operate them;
how — and when — to repair or replace them, and considerably more. Stay tuned!
THIS ISSUE:
The Mystery of Motor Frame Size
Primer on Two-Speed Motors

Introduction Rerating and Temperatures

Industrial electric motors have been available for nearly a The ability to re-rate motor frames to get more horsepower
century. In that time there have been a great many changes. in a frame has been brought about mainly by improvements
One of the most obvious has been the ability to pack more made in insulating materials. As a result of this improved
horsepower in a smaller physical size. Another important insulation, motors can now be run much hotter. This allows
achievement has been the standardization of motors by the more horsepower in a compact frame. For example, the origi-
National Electric Manufacturers Association (NEMA). nal NEMA frame sizes ran at very low temperatures. The “U”
A key part of motor interchangeability has been the stan- frame motors were designed for use with Class A insulation,
dardization of frame sizes. This means that the same horse- which has a rating of 105° C. The motor designs were such
power, speed, and enclosure will normally have the same that the capability would be used at the hottest spot within
frame size from different motor manufacturers. Thus, a motor the motor. “T” frame motor designs are based on utilizing
from one manufacturer can be replaced with a similar motor Class B insulation with a temperature rating of 130° C. This
from another company provided they are both in standard increase in temperature capability made it possible to pack
frame sizes. more horsepower into the same size frame. To accommo-
date the larger mechanical horsepower capability, shaft and
Three Generations bearing sizes had to be increased. Thus, you will find that
The standardization effort over the last forty-plus years has the original 254 frame (5 HP at 1,800 RPM) has a 11⁄8" shaft.
resulted in one original grouping of frame sizes called “origi- The 254U frame (7½ HP at 1,800 RPM) has a 13⁄8" shaft, and
nal.” In 1952, new frame assignments were made. These were the current 254T frame (15 HP at 1800 RPM) has a 15⁄8" shaft.
called “U frames.” The current “T frames” were introduced in Bearing diameters were also increased to accommodate the
1964. “T” frames are the current standard and most likely will larger shaft sizes and heavier loads associated with the higher
continue to be for some time in the future. horsepower.
Even though “T” frames were adopted in 1964, there are
still a great many “U” frame motors in service that will have Frame Size Basis
to be replaced in the future. Similarly there are also many of On page 14 you will find a Baldor frame size chart that is a
the original frame size motors (pre-1952) that will reach the great reference on “T” frame, “U” frame and original frame
end of their useful life and will have to be replaced. For this motors. Most of the dimensions are standard dimensions
reason it is desirable to have reference material available on that are common to all motor manufacturers. One exception
frame sizes and some knowledge of changes that took place to this is the “C” dimension (overall motor length) which will
as a part of the so-called re-rate programs. change from one manufacturer to another.

Frame Size Reference Tables Fractional Horsepower Motors

Tables 1 and 2 show the standard frame size assignments The term “fractional horsepower” is used to cover those
for the three different eras of motors. As you will note, these frame sizes having two-digit designations as opposed to the
tables are broken down for open drip proof (Table 1) and three-digit designations that are found in Tables 1 and 2.
totally enclosed (Table 2). You will also find that for each The frame sizes that are normally associated with industrial
horsepower rating and speed, there are three different frame fractional horsepower motors are 42, 48, and 56. In this case,
sizes — first is the original frame size; the middle one is the each frame size designates a particular shaft height, shaft
“U frame” size; and the third one is the “T frame.” These are diameter, and face or base mounting hole pattern. In these
handy reference tables since they give general information motors specific frame assignments have not been made
for all three vintages of three-phase motors in integral horse- by horsepower and speed, so it is possible that a particular
power frame sizes. horsepower and speed combination might be found in three
One important item to remember is that the base mount- different frame sizes. In this case, for replacement it is essen-
ing hole spacing (“E” and “F” dimensions) and shaft height tial that the frame size be known as well as the horsepower,
(“D” dimension) for all frames having the same three dig- speed and enclosure. The derivation of the two-digit frame
its — regardless of vintage — will be the same. number is based on the shaft height in sixteenths of an inch.

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Table 1  Open Drip-Proof
THREE PHASE FRAME SIZES - GENERAL PURPOSE
RPM 3600 1800 1200 900
NEMA 1964 1964 1964 1964
Orig. 1952 Orig. 1952 Orig. 1952 Orig. 1952
Program Rerate Rerate Rerate Rerate
Rerate Rerate Rerate Rerate
HP
1 203 182 143T 204 184 145T 225 213 182T
1.5 203 182 143T 204 184 145T 224 184 182T 254 213 184T
2 204 184 145T 224 184 145T 225 213 184T 254 215 213T
3 224 184 145T 225 213 182T 254 215 213T 284 254U 215T
5 225 213 182T 254 215 184T 284 254U 215T 324 256U 254T
7.5 254 215 184T 284 254U 213T 324 256U 254T 326 284U 256T
10 284 254U 213T 324 256U 215T 326 284U 256T 364 286U 284T
15 324 256U 215T 326 284U 254T 364 324U 284T 365 326U 286T
20 326 284U 254T 364 286U 256T 365 326U 286T 404 364U 324T
25 364S 286U 256T 364 324U 284T 404 364U 324T 405 365U 326T
30 364S 324US 284TS 365 326U 286T 405 365U 326T 444 404U 364T
40 365S 326US 286TS 404 364U 324T 444 404U 364T 445 405U 365T
50 404S 364US 324TS 405S 365US 326T 445 405U 365T 504 444U 404T
60 405S 365US 326TS 444S 404US 364T 504 444U 404T 505 445U 405T
75 444S 404US 364TS 445S 405US 365T 505 445U 405T — — 444T
100 445S 405US 365TS 504S 444US 404T — — 444T — — 445T
125 504S 444US 404TS 505S 445US 405T — — 445T —
150 505S 445US 405TS — 444T —
200 444TS — 445T —
250 445TS —

Table 2  Totally Enclosed, Fan-Cooled

THREE PHASE FRAME SIZES - GENERAL PURPOSE
RPM 3600 1800 1200 900
NEMA 1964 1964 1964 1964
Orig. 1952 Orig. 1952 Orig. 1952 Orig. 1952
Program Rerate Rerate Rerate Rerate
Rerate Rerate Rerate Rerate
HP
1 203 182 143T 204 184 145T 225 213 182T
1.5 203 182 143T 204 184 145T 224 184 182T 254 213 184T
2 204 184 145T 224 184 145T 225 213 184T 254 215 213T
3 224 184 182T 225 213 182T 254 215 213T 284 254U 215T
5 225 213 184T 254 215 184T 284 254U 215T 324 256U 254T
7.5 254 215 213T 284 254U 213T 324 256U 254T 326 284U 256T
10 284 254U 215T 324 256U 215T 326 284U 256T 364 286U 284T
15 324 256U 254T 326 284U 254T 364 324U 284T 365 326U 286T
20 326 286U 256T 364 286U 256T 365 326U 286T 404 364U 324T
25 365S 324U 284TS 365 324U 284T 404 364U 324T 405 365U 326T
30 404S 326US 286TS 404 326U 286T 405 365U 326T 444 404U 364T
40 405S 364US 324TS 405 364U 324T 444 404U 364T 445 405U 365T
50 444S 365US 326TS 444S 365US 326T 445 405U 365T 504 444U 404T
60 445S 405US 364TS 445S 405US 364T 504 444U 404T 505 445U 405T
75 504S 444US 365TS 504S 444US 365T 505 445U 405T — — 444T
100 505S 445US 405TS 505S 445US 405T — 444T — — 445T
125 444TS — 444T — 445T —
150 445TS — 445T

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 TECHNICAL

Leading Provider of Energy Efficient

Industrial Electric Motors and Drives

NEMA Keyseat NEMA Keyseat

Shaft Dimensions Shaft Dimensions
(U) (R) (S) (U) (R) (S)
3/8 21/64 FLAT 1-7/8 1-19/32 1/2
1/2 29/64 FLAT 2-1/8 1-27/32 1/2
5/8 33/64 3/16 2-3/8 2-1/64 5/8
7/8 49/64 3/16 2-1/2 2-3/16 5/8
1-1/8 63/64 1/4 2-7/8 2-29/64 3/4
1-3/8 1-13/64 5/16 3-3/8 2-7/8 7/8
1-5/8 1-13/32 3/8 3-7/8 3-5/16 1

Drawings represent standard TEFC general purpose motors.

*Dimensions are for reference only.

*Contact your local Baldor Sales Office for “C” Dimensions. Dimensions - N, O, P, AB and XO are specific to Baldor.

NEMA QUICK REFERENCE CHART

NEMA
D E 2F H N O P U V AA AB AH AJ AK BA BB BD XO TAP
FRAME
9/32
42 2-5/8 1-3/4 1-11/16 1-1/2 5 4-11/16 3/8 1-1/8 3/8 4-1/32 1-5/16 3-3/4 3 2-1/16 1/8 4-5/8 1-9/16 1/4-20
SLOT
11/32
48 3 2-1/8 2-3/4 1-7/8 5-7/8 5-11/16 1/2 1-1/2 1/2 4-3/8 1-11/16 3-3/4 3 2-1/2 1/8 5-5/8 2-1/4 1/4-20
SLOT
56 3 11/32 2-7/16
3-1/2 2-7/16 6-7/8 6-5/8 5/8 1-7/8 1/2 5 2-1/16 5-7/8 4-1/2 2-3/4 1/8 6-1/2 2-1/4 3/8-16
56H 5 SLOT 2-1/8
143T 4
3-1/2 2-3/4 11/32 2-1/2 6-7/8 6-5/8 7/8 2-1/4 3/4 5-1/4 2-1/8 5-7/8 4-1/2 2-1/4 1/8 6-1/2 2-1/4 3/8-16
145T 5
182 4-1/2 2-11/16 7/8 2-1/4 2-1/8 5-7/8 4-1/2 1/8 6-1/2 3/8-16
184 5-1/2 2-11/16 7/8 2-1/4 2-1/8 5-7/8 4-1/2 1/8 6-1/2 3/8-16
4-1/2 3-3/4 13/32 8-11/16 7-7/8 3/4 5-7/8 2-3/4 2-3/8
182T 4-1/2 3-9/16 1-1/8 2-3/4 2-5/8 7-1/4 8-1/2 1/4 9 1/2-13
184T 5-1/2 3-9/16 1-1/8 2-3/4 2-5/8 7-1/4 8-1/2 1/4 9 1/2-13
213 5-1/2 3-1/2 1-1/8 3 2-3/4
215 7 3-1/2 1-1/8 3 2-3/4
5-1/4 4-1/4 13/32 10-1/4 9-9/16 1 7-3/8 7-1/4 8-1/2 3-1/2 1/4 9 2-3/4 1/2-13
213T 5-1/2 3-7/8 1-3/8 3-3/8 3-1/8
215T 7 3-7/8 1-3/8 3-3/8 3-1/8
254U 8-1/4 4-1/16 1-3/8 3-3/4 3-1/2
256U 10 4-1/16 1-3/8 3-3/4 3-1/2
6-1/4 5 17/32 12-7/8 12-15/16 1 9-5/8 7-1/4 8-1/2 4-1/4 1/4 10 — 1/2-13
254T 8-1/4 4-5/16 1-5/8 4 3-3/4
256T 10 4-5/16 1-5/8 4 3-3/4
284U 9-1/2 5-1/8 1-5/8 4-7/8 4-5/8
286U 11 5-1/8 1-5/8 4-7/8 4-5/8
284T 9-1/2 4-7/8 1-7/8 4-5/8 4-3/8
7 5-1/2 17/32 14-5/8 14-5/8 1-1/2 13-1/8 9 10-1/2 4-3/4 1/4 11-1/4 — 1/2-13
286T 11 4-7/8 1-7/8 4-5/8 4-3/8
284TS 9-1/2 3-3/8 1-5/8 3-1/4 3
286TS 11 3-3/8 1-5/8 3-1/4 3
324U 10-1/2 5-7/8 1-7/8 5-5/8 5-3/8
326U 12 5-7/8 1-7/8 5-5/8 5-3/8
324T 10-1/2 5-1/2 2-1/8 5-1/4 5
8 6-1/4 21/32 16-1/2 16-1/2 2 14-1/8 11 12-1/2 5-1/4 1/4 13-3/8 — 5/8-11
326T 12 5-1/2 2-1/8 5-1/4 5
324TS 10-1/2 3-15/16 1-7/8 3-3/4 3-1/2
326TS 12 3-15/16 1-7/8 3-3/4 3-1/2
364U 11-1/4 6-3/4 2-1/8 6-3/8 18 6-1/8
365U 12-1/4 6-3/4 2-1/8 6-3/8 18 6-1/8
364T 11-1/4 6-1/4 2-3/8 5-7/8 18-1/16 5-5/8
9 7 21/32 18-1/2 19-1/2 3 11 12-1/2 5-7/8 1/4 13-3/8 — 5/8-11
365T 12-1/4 6-1/4 2-3/8 5-7/8 18-1/16 5-5/8
364TS 11-1/4 4 1-7/8 3-3/4 18-1/16 3-1/2
365TS 12-1/4 4 1-7/8 3-3/4 18-1/16 3-1/2
404U 12-1/4 7-3/16 2-3/8 7-1/8 19-1/4 6-7/8
405U 13-3/4 7-3/16 2-3/8 7-1/8 19-1/4 6-7/8
404T 12-1/4 7-5/16 2-7/8 7-1/4 19-5/16 7
10 8 13/16 21-5/16 22-1/2 3 11 12-1/2 6-5/8 1/4 13-7/8 — 5/8-11
405T 13-3/4 7-5/16 2-7/8 7-1/4 19-5/16 7
404TS 12-1/4 4-1/2 2-1/8 4-1/4 19-5/16 4
405TS 13-3/4 4-1/2 2-1/8 4-1/4 19-5/16 4
444U 14-1/2 8-5/8 24.24 27.57 2-7/8 8-5/8 3 22.68 8-3/8
445U 16-1/2 8-5/8 24.24 27.57 2-7/8 8-5/8 3 22.68 8-3/8
444T 14-1/2 8-9/16 24.24 27.57 3-3/8 8-3/8 4 22.68 8-1/4
445T 16-1/2 8-9/16 24.24 27.57 3-3/8 8-3/8 4 22.68 8-1/4
447T 20 8-9/16 24.24 27.57 3-3/8 8-3/8 4 23.86 8-1/4
11 9 13/16 14 16 7-1/2 1/4 16-3/4 — 5/8-11
449T 25 8-9/16 24.24 27.57 3-3/8 8-1/2 4 23.86 8-1/4
444TS 14-1/2 4-13/16 24.24 27.57 2-3/8 4-5/8 4 22.68 4-1/2
445TS 16-1/2 4-13/16 24.24 27.57 2-3/8 4-5/8 4 22.68 4-1/2
447TS 20 4-13/16 24.24 27.57 2-3/8 4-5/8 4 23.86 4-1/2
449TS 25 4-13/16 24.24 27.57 2-3/8 4-3/4 4 23.86 4-1/2

The above chart provides typical Baldor•Reliance motor dimensions. BA Frame

D E
NEMA FRAMES PRIOR TO 1953
F N U V BA
For more exact dimensional data, please check the specific drawing NEMA C-Face
Dimensions 66 4-1/8 2-15/16 2-1/2 2-1/4 3/4 2-1/4 3-1/8
203 2-3/4
for each catalog number. NEMA states only a minimum value for AA 143-5TC 2-3/4 204
5 4
3-1/4
2-7/16 3/4 2 3-1/8
224 3-3/8
dimension. AA dimensions shown in chart are Baldor typical values 182-4TC 3-1/2 225
5-1/2 4-1/2
3-3/4
3-1/4 1 3 3-1/2
254 6-1/4 5 4-1/8 3-7/16 1-1/8 3-3/8 4-1/4
meeting or exceeding NEMA. Please check motor drawing for actual 213-5TC 4-1/4 284 7 5-1/2 4-3/4 4-1/4 1-1/4 3-3/4 4-3/4
324 5-1/4
dimensions. 254-6TC 4-3/4 326
8 6-1/4
6
5-3/8 1-5/8 4-7/8 5-1/4
364 5-5/8
9 7 5-5/8 1-7/8 5-3/8 5-7/8
365 6-1/8
BALDOR ELECTRIC COMPANY 404 6-1/8
Frame L449T is not included in this chart. Please refer to the Large AC P.O. BOX 2400
405
10 8
6-7/8
6-3/8 2-1/8 6-1/8 6-5/8
444 7-1/4
motor chart, or to the specific motor drawings for L449T dimensions. FORT SMITH, ARKANSAS 445
11 9
8-1/4
7-1/8 2-3/8 6-7/8 7-1/2

72902-2400 U.S.A. 504

12-1/2 10
8
8-5/8 2-7/8 8-3/8 8-1/2
505 9

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You can figure that a 48-frame motor will have a shaft height coupling. They are not intended for applications where
of 48 divided by 16 or 3 inches. Similarly, a 56-frame motor belts are used to drive the load.
would have a shaft height of 3½ inches. The largest of the cur- T “T” at the end of the frame size indicates that the motor is
rent fractional horsepower frame sizes is a 56-frame that is of the 1964 and later “T” frame vintage.
available in horsepower greater than those normally associ- U A “U” at the end of the frame size indicates that the motor
ated with fractionals. For example, 56-frame motors are built falls into the “U” frame size assignment (1952 to 1964) era.
in horsepower up to 3 HP and, in some cases, 5 HP. For this Y When a “Y” appears as a part of the frame size it means
reason calling motors with 2-digit frame sizes “fractionals” is that the motor has a special mounting configuration. It is
somewhat misleading. impossible to tell exactly what the special configuration
is, but it does denote that there is a special non-standard
Integral Horsepower Motors mounting.
The term “integral-horsepower motor” generally refers to Z Indicates the existence of a special shaft that could be lon-
those motors having three-digit frame sizes such as 143T or ger, larger, or have special features such as threads, holes,
larger. When dealing with these frame sizes one rule of thumb etc. “Z” indicates only that the shaft is special in some un-
applies: the centerline shaft height (“D” dimension) above defined way.
the bottom of the base is the first two digits of the frame size (* The NEMA chart provides typical Baldor•Reliance motor
divided by four. For example, a 254T frame would have a shaft dimensions. For more exact dimensional data, please check
height of 25 ÷ 4 = 6.25 inches. Although the last digit does not the specific drawing for each catalog number. NEMA states
directly relate to an “inch” dimension, larger numbers do in- only a minimum value for AA dimension. AA dimensions
dicate that the rear bolt holes are moved further away from shown in chart are Baldor typical values meeting or exceeding
the shaft end bolt holes (the “F” dimension becomes larger). NEMA. Please check motor drawing for actual dimensions.)
Frame L449T is not included in this chart. Please refer to
Variations the Large AC motor chart, or to the specific motor drawings
In addition to the standard numbering system for frames, for L449T dimensions.
there are some variations that will appear; these are itemized
below along with an explanation of what the various letters Primer On Two-Speed Motors
represent. There seems to be a lot of mystery involved in two speed mo-
C Designates a “C” face (flange) mounted motor. This is the tors but they are really quite simple. They can first be divided
most popular type of face-mounted motor and has a spe- into two different winding types:
cific bolt pattern on the shaft end to allow mounting. The Two-speed, two-winding. The two winding motor is made
critical items on “C” face motors are the “bolt circle” (AJ in such a manner that it is really two motors wound into one
dimension), register (also called rabbet), diameter (AK di- stator. One winding, when energized, gives one of the speeds.
mension) and shaft size (U dimension). C flange motors When the second winding is energized, the motor takes on
always have threaded mounting holes in the face of the the speed that is determined by the second winding. The two-
motor. speed, two-winding motor can be used to get virtually any
D The “D” flange has a special type of mounting flange in- combination of normal motor speeds and the two different
stalled on the shaft end; i.e. — the flange diameter is larg- speeds need not be related to each other by a 2:1 speed factor.
er than the body of the motor and it has clearance holes Thus, a two-speed motor requiring 1,750 RPM and 1,140 RPM
suitable for mounting bolts to pass through from the back would, of necessity, have to be a two-winding motor.
of the motor into threaded holes in the mating part. “D” Two-speed, one-winding. The second type of motor is
flange motors are not as popular as “C” flange motors. the two-speed, single-winding motor. In this type of motor,
H Used on some 56-frame motors, “H” indicates that the a 2:1 relationship between the low and high speed must ex-
base is suitable for mounting in either 56, 143T, or 145T ist. Two-speed, single-winding motors are of the design that
mounting dimensions. is called “consequent pole.” These motors are wound for one
J This designation is used with 56-frame motors and indi- speed, but when the winding is reconnected the number of
cates that the motor is made for “jet pump” service with a magnetic poles within the stator is doubled and the motor
threaded stainless steel shaft and standard 56C face. speed is reduced to one-half of the original speed. The two-
JM The letters “JM” designate a special pump shaft originally speed, one-winding motor is, by nature, more economical to
designed for a “mechanical seal;” this motor also has a C manufacture than the two-speed, two-winding motor. This is
face. because the same winding is used for both speeds and the
JP Similar to the JM style of motor having a special shaft, the slots in which the conductors are placed within the motor do
JP motor was originally designed for a “packing” type of not have to be nearly as large as they would have to be to ac-
seal. The motor also has a C face. commodate two separate windings that work independently.
S The use of the letter “S” in a motor frame designates that Thus, the frame size on the two-speed, single-winding motor
the motor has a “short shaft.” Short shaft motors have can usually be smaller than on an equivalent two-winding
shaft dimensions that are smaller than the shafts associ- motor.
ated with the normal frame size. Short shaft motors are Load classification. A second item that generates a good
designed to be directly coupled to a load through a flexible deal of confusion in selecting two speed motors is the load

FEBRUARY 2017 Power Transmission Engineering 41

 TECHNICAL

classification for which these motors are to be used. In this readily available in constant torque and variable torque.
case, the type of load to be driven must be defined and the Two-speed, constant-horsepower motors are usually only
motor is selected to match the load requirement. available on a custom order basis.
The three types available are: constant torque, variable Two-speed, single-phase motors. Two-speed, single-
torque, and constant horsepower. For more details on load phase motors for constant torque requirements are more dif-
types please refer to “Understanding Torque” in this booklet. ficult to supply since there is a problem in providing a starting
Constant torque. Constant torque loads are those types switch that will operate at the proper time for both speeds.
of loads where the torque requirement is independent of Thus the normal two-speed, single-phase motor is offered as
speed. This type of load is the normally occurring load on a variable-torque motor in a permanent-split capacitor con-
such things as conveyors, positive displacement pumps, ex- figuration. The permanent-split capacitor motor has very low
truders, hydraulic pumps, packaging machinery, and other starting torque but is suitable for use on small, centrifugal
similar types of loads. pumps and fans.
Variable torque. A second load type that is very different
from constant torque is the kind of load presented to a mo- Summary
tor by centrifugal pumps and blowers. In this case, the load The use of two-speed motors in the future will grow quite rap-
torque requirement changes from a low value at low speed to idly as industrial motor users begin to realize the desirability
a very high value at high speed. On a typical variable torque of using this type of motor on exhaust fans and circulating
load, doubling the speed will increase the torque requirement pumps, so that air flow and water flow can be optimized to
by 4 times and the horsepower requirement by 8 times. Thus, suit the conditions that exist in a plant or a process. Very dra-
on this type load, brute force must be supplied at the high matic savings in energy can be achieved by utilizing the two-
speed and much reduced levels of horsepower and torque speed approach.
are required at the low speed. A typical two-speed, variable For more information:
torque motor might have a rating of 1 HP at 1,725 and .25 HP Baldor Electric Company/Member of the ABB Group
at 850 RPM. 5711 R. S. Boreham Jr. Street
The characteristics of many pumps, fans, and blowers are Fort Smith AR 72901
Phone: (479) 648.5694
such that a speed reduction to one-half results in an output at www.baldor.com
the low speed which may be unacceptable. Thus, many two-
speed, variable-torque motors are made with a speed combi-
nation of 1,725/1,140 RPM. This combination gives an output
from the fan or pump of roughly one-half when the
low speed is utilized.
Constant horsepower. The final type of
two-speed motor utilized is the two-speed,
constant-horsepower motor. In this case
the motor is designed so that the horse-
power stays constant when the speed is
reduced to the low value. In order to do
this it is necessary for the motor’s torque
to double when it is operating in low-
speed mode. The normal application
for this type of motor is on metal work-
ing processes such as drill presses, lathes,
milling machines, and other similar metal
removing machines. The requirement for
constant horsepower can perhaps be best vi-
sualized when you consider the requirements
of a simple machine like a drill press. In this case,
when drilling a large hole with a large drill, the speed is
low but the torque requirement is very high. Compare
that to the opposite extreme of drilling a small hole when
the drill speed must be high but the torque requirement is
low. Thus, there is a requirement for torque to be high when
speed is low and torque to be low when speed is high. This is
For Related Articles Search
the “constant-horsepower” scenario.
The constant-horsepower motor is the most expensive motor basics
two-speed motor. Three-phase, two-speed motors are quite at www.powertransmission.com

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