are some commonly asked questions regarding energy efficient motors.
As time goes on different questions and answers will be put on this
page for the purpose of educating industry. The Department of Energy
has developed the MOTORMASTER+ program. This is a sophisticated
software based program which can analyze electric motors in a plant
and will determine their efficiencies and costs. EASTLAND INDUSTRIES,
INC. is a MOTORMASTER+ PARTNER and also an ALLIED PARTNER with the
Department of Energy.
Please contact Eastland Industries at
for further information in developing your program.
Energy Efficient Motors: FAQ's
1. What is an energy
2. How is an energy
efficient motor different than a standard motor?
3. Are all new motors
energy efficient motors?
4. Where can I buy an
energy efficient motor?
5. Are energy efficient
single-phase motors available?
6. Do energy efficient
motors require more maintenance?
7. What horsepower, speed,
and voltage ranges are available?
8. Can an energy efficient
motor replace my present U- or T-frame motor?
9. Should I rewind my
standard-efficiency motor or purchase an energy efficient motor?
10. Can a standard motor
be rewound as an energy efficient motor?
11. What is the efficiency
of an energy efficient motor at different load points?
12. Do energy efficient
motors maintain the same percentage edge over standard?
13. Do energy
efficient-motors require more starting current?
14. What is the power
factor of an energy efficient motor?
15. I have heard different
types of efficiencies quoted. What are they?
16.What are IEEE 112, CSA
C-390-M1993, IEC 34-2 and JEC 37?
17. Can I compare motor
efficiencies using nameplate data?
18. Is the service factor
any different from that of a standard motor?
19. How much do energy
efficient motors cost?
20. What is the payback
period for selecting an energy efficient versus a standard-efficiency
21. Do terms such as
"premium", high", "super", "ultra", "plus", or "extra" describe
specific motor efficiency characteristics?
22. Are oversized motors
less efficient than motors that are matched to their load?
23. Don't energy efficient
motors always cost less to operate?
24. Don't energy efficient
motors operate "cooler"?
25. Do energy efficient
motors suffer a loss in efficiency when they are repaired?
26. Don't energy efficient
motors have to be oversized because they don't develop enough starting
27. Isn't the efficiency
gain insignificant between large standard and energy efficient motors?
28. Don't energy efficient
motors have a longer expected service life due to their being equipped
with better and oversized bearings?
29. Aren't energy
efficient motors unsuitable for adjustable speed drive applications?
30. Isn't a quality rewind
of an old motor just as good as purchasing a new energy efficient
1. What is an
energy efficient motor?
An "energy efficient" motor produces the same shaft output power (hp),
but uses less input power (kW) than a standard-efficiency motor.
Energy efficient motors must have nominal full-load efficiencies that
meet or exceed the NEMA threshold standards.
Many motor manufacturers produce models significantly exceeding the
NEMA standard. These may have the term "premium" or other superlatives
in the model name, but there is no NEMA standard for any terminology
other than "energy efficient."
2. How is an
energy efficient motor different than a standard motor?
Energy efficient motors are manufactured using the same frame as a
standard T-frame motor, but have:
- Higher quality and thinner steel laminations in the stator.
- More copper in the windings.
- Optimized air gap between the rotor and stator.
- Reduced fan loses.
- Closer matching tolerances.
- A greater length.
3. Are all new
motors energy efficient motors?
No. You generally have to ask for them.
Starting in October 1997, however, the Energy Policy Act of 1992
requires most general purpose induction motors between 1 and 200
horsepower (hp) to meet more stringent minimum efficiency standards.
4. Where can I
buy an energy efficient motor?
Energy efficient motors can be purchased directly from Eastland
Industries at 1-888-547-6500
5. Are energy
efficient single-phase motors available?
NEMA has no standard for "energy efficient" single-phase motors, but
efficiency ranges widely among models. A few manufacturers are
beginning to produce higher efficiency lines of single-phase motors.
6. Do energy
efficient motors require more maintenance?
No. Energy efficient motors have the same maintenance requirements as
horsepower, speed, and voltage ranges are available?
Energy efficient motors are available for most sizes 1 to 500 hp at
speeds of 3600, 1800, 1200, and 900 rpm and three-phase voltages of
208, 230, 460, 575 and higher.
8. Can an energy
efficient motor replace my present U- or T-frame motor?
Yes. Since T-frame energy efficient motors generally use the same
frame casting as a standard motor, standard T-frame to energy
efficient T-frame should be a straight replacement. An adapter or
transition base is required for a U-frame to T-frame replacement. In
addition, some manufacturers now make energy efficient U-frame motors.
Contact Eastland Industries at 1-888-547-6500
9. Should I
rewind my standard-efficiency motor or purchase an energy efficient
An energy efficient motor will result in lower energy costs when
compared with a rewound standard-efficiency motor. Its cost
effectiveness will depend on the hours operated, motor efficiencies,
utility rates, and the difference in cost between the rewind and the
energy efficient motor.
Current rewind shop practices are outlined in the EPRI/BPA report
Industrial Motor Repair in the United States: Current Practice and
Opportunities for Improved Energy-Efficiency and the companion
document Quality Electric Motor Repair: A Guidebook for Electric
10. Can a
standard motor be rewound as an energy efficient motor?
It is sometimes possible for a standard motor to be rewound with
slightly larger diameter wire. This rewind procedure can slightly
improve the efficiency and adversely increase the starting current of
a standard motor above its initial level. However, the efficiency
would still be lower than that of a new energy efficient motor because
of its unique physical characteristics. Energy efficient motors can be
rewound to maintain their original efficiency.
11. What is the
efficiency of an energy efficient motor at different load points?
The efficiency of any motor varies with such factors as size, speed,
and loading. Energy efficient motors offer performance improvements
over standard-efficiency motors under full, partial, and unloaded
12. Do energy
efficient motors maintain the same percentage edge over standard?
Yes. Most manufacturers are designing their energy efficient motors to
provide peak efficiency at 75 percent to 100 percent load. Typically
efficiency stays fairly constant from full down to 50 percent load,
but the power factor drops significantly.
13. Do energy
efficient-motors require more starting current?
Sometimes. There are two terms (often misused) pertaining to starting
current, "inrush" current and "locked rotor" current. The familiar
"locked rotor" current begins after contact closure and tapers off
over several seconds while the motor accelerates. Locked rotor current
is limited by NEMA standards to roughly six times full load current
for both standard and energy efficient Design B motors. Design E motor
standards are consistent with European standards and allow a higher
locked rotor current in most horsepower ranges, roughly 10 times full
The more insidious aspect of starting current is the momentary
"inrush" current, which persists for less than a hundredth of a second
and can substantially exceed locked rotor current. Inrush current can
spike as high as 13 times full-load current in standard motors and as
high as 20 times full-load current in Design E and energy efficient
Design B motors. Inrush current is too brief to trip thermal
protection devices, but energy efficient motors powered through
magnetic circuit protectors can sometimes experience nuisance stating
14. What is the
power factor of an energy efficient motor?
Power factors vary tremendously depending on motor loading
manufacturer. While some energy efficient motor models offer power
factor improvements of two to five percent, others have lower power
factors than their standard motor counterparts.
Overall, replacement of a standard with an energy efficient motor
isn't likely to have much influence on power factor. On the average, a
power factor improvement of less than one percent is expected. In any
event, power factor correction is easily achieved by adding external
15. I have heard
different types of efficiencies quoted. What are they?
The following motor efficiency definitions are used: Quoted, Nominal,
Average, Expected, Calculated, Minimum, Guaranteed, and Apparent. The
most commonly used are Nominal and Minimum, defined as:
- Nominal efficiency is the efficiency that goes on the nameplate.
It is the lower bound an efficiency band that brackets the
statistical mean full load efficiency of a large number of motors of
the same design. NEMA specified these bands, which are fairly
narrow, e.g. spanning about 1 percent in the 85 percent efficiency
range. The band becomes tighter at higher efficiency.
- Minimum efficiency. For every nominal efficiency ban prescribed
above by NAME, a minimum efficiency is also prescribed. Individual
motor efficiency is allowed to vary from nominal, but no motors are
supposed to fall below the minimum. Minimum efficiency is set equal
to the nominal value of two bands lower. It represents losses about
20 percent greater than nominal losses.
16.What are IEEE
112, CSA C-390-M1993, IEC 34-2 and JEC 37?
These are motor efficiency test or product standards.
- The IEEE Standard 112 Method B motor efficiency testing
methodology is the most commonly used North American Standard.
- CSA C-390-M1993, is a Canadian-developed standard.
- IEC 34-2 is the European motor test standard.
- JEC 37 is the Japanese motor test standard
17. Can I
compare motor efficiencies using nameplate data?
Per NEMA-MG1-12.54.2, the efficiency of Design A and Design B motors
in the 1-500 hp range for frames in accordance with MG13 shall be
marked in the motor nameplate. As nameplate full-load efficiencies are
rounded values, you should always obtain nominal full- and part-load
efficiency values from the motor manufacturer or MotorMaster+.
18. Is the
service factor any different from that of a standard motor?
No. Service factors for both standard and energy efficient motors
range from 1 to 1.25 with about 88 percent of motors at 1.15.
19. How much do
energy efficient motors cost?
Generally, they average 15 to 30 percent more than standard motors,
but depending on the specific motor manufacturer and market
competition, they can be even less expensive. It is often possible to
negotiate a lower price premium when purchasing a large quantity of
energy efficient motors. The price premium per horsepower is lower for
the larger motor ratings.
20. What is the
payback period for selecting an energy efficient versus a
The payback period varies according to the purchase scenario under
consideration, cost difference, hours of operation, electrical rates,
motor loading, and difference in motor efficiencies. For new purchase
decisions, the simple payback on the incremental cost of a
continuously operated energy efficient motor can be recovered through
energy savings in well under two years.
21. Do terms
such as "premium", high", "super", "ultra", "plus", or "extra"
describe specific motor efficiency characteristics?
Manufacturers are free to select descriptive terminology for use in
identifying and marketing motor lines. The term energy efficient,
however is restricted to motors meeting the NEMA MG1 Table 12-10
full-load efficiency standards.
oversized motors less efficient than motors that are matched to their
Surveys indicated that most motors are underloaded by one-fourth to
one-third. The efficiency of typical motor designs peaks at three
quarters load and remains relatively uniform down to the 50 percent
load point. A motor replacement analysis should be conducted for
motors operating below 40 percent of their full-rated load.
Oversized motors will require greater starting currents and operate
with a lower power factor than motors that are closely matched to
23. Don't energy
efficient motors always cost less to operate?
Energy efficient motors have a lower rotor and stator resistance and
thus a higher inrush current and full-load speed than
standard-efficiency motors. Speed changes significantly affect the
power draw by centrifugal loads. The shaft power requirements for a
centrifugal fan or pump loads varies as the cube of the speed while
the flow of air or fluid discharge varies linearly with speed.
An increase in driven-equipment load can result in a greater power
of kilowatt draw despite the lower inherent losses of the energy
The cost penalty due to operating at a higher full-load speed is
related to load characteristics. For instance, a motor driving a pump
which fills a reservoir tank may operate in an on/off mode. While the
kilowatt draw may be higher, the operating time is reduced due to the
provision of increased flow. In contrast, given a continuously
operating system, the extra pumping capacity may be wasted in
throttling and friction losses. The entire system of process should be
examined prior to replacing a standard with an energy efficient motor.
Also, not all energy efficient motors have higher speeds than their
24. Don't energy
efficient motors operate "cooler"?
External temperature readings are often interpreted as a measure of
If two motors are identical, the one with the lower losses will
indeed operate at a lower temperature due to decreased internal heat
production. Lower losses, however, result in diminished need for
ventilation air, and fan cooled energy efficient motors are often
equipped with a smaller fan to reduce windage losses. The consequence
of fan design modifications is that an energy efficient motor may have
a running temperature as high or higher than that of a
standard-efficiency motor with significantly higher losses.
25. Do energy
efficient motors suffer a loss in efficiency when they are repaired?
Not necessarily. Efficiency losses can occur in either standard or
energy efficient motors when poor quality control is observed. The
core can be damaged by excess heat during winding removal. Any
deviation from original wire gage and winding pattern generally
increases losses. Machine work that alters original clearance and
tolerance, and substitution of nonequivalent parts such as sealed
bearings for shielded bearings can also reduce efficiency. Standard
and energy efficient motors have comparable susceptibility to these
26. Don't energy
efficient motors have to be oversized because they don't develop
enough starting torque?
The same minimum allowable locked rotor (starting) torque is specified
by NEMA for all Design A and B motors regardless of efficiency. NEMA
standards for Design E motor locked rotor torque are higher than
Designs A and B levels for some horsepower and speed combinations and
lower for others. While some energy efficient motors may exhibit a
slightly lower locked rotor torque than their standard-efficiency
counterparts, no problems should be posed except for special
applications such as heavily loaded conveyors. NEMA Design C motors
should probably be specified for such applications anyway. Full-load,
breakdown and locked rotor torque values are available for most energy
efficient and standard motor models within the MotorMaster+
Electric Motor Selection software.
27. Isn't the
efficiency gain insignificant between large standard and energy
While the percentage improvement obtainable decreases as motor size
increases, the energy and dollar savings per hour of motor operation
increases substantially. A one-point efficiency improvement for a 100
hp motor will save more energy than a nine-point efficiency gain for a
ten hp motor.
The price premium per kW saved is comparable across a broad range
of hp. Small improvements are worth pursuing.
28. Don't energy
efficient motors have a longer expected service life due to their
being equipped with better and oversized bearings?
Most motor bearings are oversized. Improved bearings are available for
both standard and energy efficient motors. Motor life is not
significantly correlated to efficiency. Conversely, it is highly
dependent upon proper application, maintenance, and environmental
energy efficient motors unsuitable for adjustable speed drive
"Severe-duty" application conditions are not affected by motor
efficiency. Energy efficient motors may, in fact, be more suited for
variable speed drive use than their standard-efficiency counterparts.
Many manufacturers now produce energy efficient ASD, inverter drive,
or inverter duty motors. These motors are provided with a totally
enclosed nonventilated enclosure or are equipped with a fixed-speed
fan or blower system.
30. Isn't a
quality rewind of an old motor just as good as purchasing a new energy
No. It is sometimes possible to slightly improve efficiency of an old
motor by using larger diameter wire or replacing aluminum wire with
copper, but it is rare. A quality rewind can usually equal, but not
exceed original efficiency.