A typical buck-boost application is 120 volts in, 12 volts out for low
voltage lighting or control circuitry. In most applications, this low
voltage transformer is field connected as an autotransformer. Buck-boost
transformers provide tremendous capabilities and flexibility in KVA
sizes and input/output voltage combinations. Basically you get 75
different transformers... all in one convenient package. Other
buck-boost applications are, where (A) low supply voltage exists because
equipment is installed at the end of a bus system; (B) the supply system
is operating at or over its design capacity; and (C) where overall
consumer demands may be so high the utility cuts back the supply voltage
to the consumer causing a “brownout." Why Use Buck-Boost Instead of
Another Type Transformer ? Take a look at the advantages and
disadvantages of using a buck-boost transformer (autotransformer)
compared to a standard isolation transformer of the proper size and
voltage combination. As you can see, the advantages are many, the
great. Buck- boost transformers are readily available from the stock of
your nearest Power Distribution Products Distributor.
No circuit isolation
Smaller & lighter
Cannot create a
5-10 times increase
Application voltages and
KVA don‘t match
voltages and KVA
Output KVA available at reduced voltage can be found by:
Actual Input Voltage Rated Input Voltage
x Output KVA = New KVA Rating.
Proper Voltage Is Critical
With nearly two-thirds of all electrical loads being A.C. motor
loads, maintenance of the proper voltage to that motor is very
important. If the supply line voltage is not maintained, motor winding
current is increased causing reduced motor torque and escalating motor
temperature, all of which results in the rapid loss of insulation life
expectancy. In addition to motor loads, the detrimental effects of low
voltage on both resistive heating loads and incandescent lighting output
is illustrated in the chart. Anytime you have a lower than standard
damage and failure can result. Buck-boost transformers are an economical
way to correct this potentially very serious problem. Anytime a line
voltage change in the 5-20% range is required, a buck-boost transformer
should be considered as your first line of defense.
Questions & Answers About Buck-Boost Transformers
1.What is a buck-boost transformer?
Buck-boost transformers are small single phase transformers designed to
reduce (buck) or raise (boost) line voltage from 5 -20%. The most common
example is boosting 208 volts to 230 volts, usually to operate a 230
volt motor such as an air conditioner compressor, from a 208 volt supply
line. Buck-boosts are a standard type of single phase distribution
transformers, with primary voltages of 120, 240 or 480 volts and
secondary typically of 12, 16, 24, 32 or 48 volts. They are available in
sizes ranging from 50 volt amperes to 10 kilo-volt amperes.
Buck-boost transformers are shipped ready to be connected for a number
of possible voltage combinations.
2. How does a buck-boost transformer differ from an insulating
A buck-boost transformer IS an insulating type transformer when it is
shipped from the factory. When it is connected at the job site, a lead
wire on the primary is connected to a lead wire on the secondary –
thereby changing the transformer’s electrical characteristics to those
of an autotransformer. The primary and secondary windings are no longer
“insulated” and secondary windings are no longer “insulated” and its KVA
3. What is the difference between a buck-boost transformer and an
When a primary lead wire and secondary lead wire of a buck-boost
transformer are connected together electrically, in a recommended
voltage bucking or boosting connection, the transformer is in all
respects, an autotransformer. However, if the interconnection between
the primary and secondary winding is not made, then the unit is an
insulating type transformer.
Buck Boost Transformer Applications
4. Why are buck boost transformers used?
Electrical and electronic equipment is designed to operate on standard
supply voltage. When the supply voltage is constantly too high or too
low, (usually more than 55%), the equipment fails to operate at maximum
efficiency. A buck and boost transformer is a simple and ECONOMICAL
means of correcting this off-standard voltage. 5.What are the most common applications for buck-boost
Boosting 208V to 230V or 240V and vice versa for commercial and
industrial air conditioning systems; boosting 110V to 120V and 240V to
277V for lighting systems; voltage correction for heating systems and
induction motors of all types. Many applications exist where supply
voltages are constantly above or below normal. 6. Can buck-boost transformers be used to power low voltage circuits?
Yes, low voltage control, lighting circuits, or other low voltage
applications requiring either 12V, 16V, 24V, 32V or 48V. The unit is
connected as an insulating transformer and the nameplate KVA rating is
the transformer’s capacity.
Buck Boost Transformer Operation and Construction
7. Why do buck-boost transformers have 4 windings?
To make them versatile! A four winding buck-boost transformer (2 primary
and 2 secondary windings) can be connected eight different ways to
provide a multitude of voltage and KVA outputs. A two winding (1 primary
& 1 secondary) buck-boost transformer can be connected only one way. 8. Will a buck-boost transformer stabilize voltage?
No. The output voltage is a function of the input voltage. If the input
voltage varies, then the output voltage will also vary by the same
Buck Boost Transformer Load Data
9. Are there any restrictions on the type of load that can be
operated from a buck-boost transformer?
No, there are no restrictions. 10. Why can a buck-boost transformer operate a KVA load many times
larger than the KVA rating on its nameplate?
Since the transformer has been auto-connected in such a fashion that the
22V secondary voltage is added to the 208V primary voltage, it produces
230V output. The autotransformer KVA is calculated:
KVA = Output Volts x Secondary Amps
KVA = 230 V x 41.67 Amps = 9.58 KVA
picture to the left illustrates the difference in physical size between
the autotransformer of 1 KVA, capable of handling a 9.58 KVA load, and
an isolation transformer capable of handling a 7.5 KVA load.
To cite an example . . . a model T-1-11683 buck-boost transformer has a
nameplate KVA rating of 1 KVA, but when it’s connected as an
boosting 208V to 230V, its KVA capacity increases to 9.58 KVA.
The key to understanding the operation of buck-boost transformers lies
the fact that the secondary windings are the only parts of the
that do the work of transforming voltage and current. In the example
above, only 22 volts are being transformed (boosted) — i.e. 208V + 22V =
230V. This 22V transformation is carried out by the secondary windings
which are designed to operate at a maximum current of 41.67 amps
(determined by wire size of windings).
Maximum Secondary Amps = nameplate KVA x 1000
Maximum Secondary Amps = 1.0 KVA x 1000
24 V 1000 VA = 41.67 amps
11. Can buck-boost transformers be used on motor loads?
Yes, either single or three phase. 12. How are single phase and three phase load Amps and load KVA
Single phase Amps = KVA x 1000
Three phase Amps = KVA x 1000
Volts x 1.73
Single phase KVA = Volts x Amps
Three phase KVA = Volts x Amps x 1.73
13. Can buck-boost transformers be used on three-phase systems as
well as single phase systems?
Yes. A single unit is used to buck or boost single phase voltage — two
or three units are used to buck or boost three phase voltage. The number
of units to be used in a three -phase installation depends on the number
of wires in the supply line. If the three-phase supply is 4 wire Y, use
three buck-boost transformers. If the 3 - phase supply is 3 wire Y
(neutral not available), use two buck-boost transformers.
14. Should buck-boost transformers be used to develop a three-phase 4
wire Y circuit from a three-phase 3 wire delta circuit?
No. A three phase “wye” buck-boost transformer connection should be used
only on a 4 wire source of supply. A delta to wye connection does not
provide adequate current capacity to accommodate unbalanced currents
flowing in the neutral wire of the 4 wire circuit.
15. Why isn’t a closed delta buck-boost connection recommended?
A closed delta buck-boost auto transformer connection requires more
transformer KVA than a “wye” or open delta connection and phase shifting
occurs on the output. Consequently the closed delta connection is more
expensive and electrically inferior to other three-phase connections.
Buck Boost Transformer Connection and Frequency
16. How does the installer or user know how to connect a buck-boost
The connection chart packed with each unit shows how to make the
appropriate connections. 17. Can 60 Hertz buck-boost transformers be used on a 50 Hertz
No. Acme buck-boost transformers should be operated only at the
frequencies recommended. However, units recommended for 50 cycle
operation are suitable for 60 cycle operation but not vice versa.
Buck Boost Transformer Nameplate Data
19. Why are buck-boost transformers shipped from the factory as
insulating transformers and not pre-connected at the factory as
A four winding buck-boost transformer can be auto connected eight
different ways to provide a multitude of voltage and KVA output
combinations. The proper transformer connection depends on the user’s
supply voltage, load voltage and load KVA. Consequently, it is more
feasible for the manufacturer to ship the unit as an insulating
transformer and allow the user to connect it on the job site in
accordance with the available supply voltage and requirements of his
load. 20. Why is the isolation transformer KVA rating shown on the
nameplate instead of the autotransformer KVA rating?
The KVA rating of a buck-boost transformer when auto connected depends
on the amount of voltage buck or boost. Since the amount of voltage buck
or boost is different for each connection, it is physically impossible
to show all of the various voltage combinations and attainable KVA
ratings on the nameplate. A connection chart showing the various
attainable single phase and three-phase connections is packed with each
Buck Boost Transformer Safety
21. Do buck-boost transformers present a safety hazard usually
associated with autotransformers?
No. Most autotransformers, if they are not of the buck-boost variety,
change voltage from one voltage class to another. (Example 480V to 240V)
In a system where one line is grounded, the user thinks he has 240V; yet
due to the primary and secondary being tied together, it is possible to
have 480V to ground from the 240V output. A buck-boost transformer only
changes the voltage a small amount, such as 208V to 240V. This small
increase does not represent a safety hazard, as compared to a buck of
480V to 240V.
Buck Boost Transformer Sound Levels
22. Are buck-boost transformers as quiet as standard isolation
Yes. However, an auto-connected buck-boost transformer will be quieter
than an isolation transformer capable of handling the same load. The
isolation transformer would have to be physically larger than the
buck-boost transformer, and small transformers are quieter than larger
ones. (Example) 1 KVA — 40 db; 75 KVA — 50 db. (db is a unit of sound
Buck Boost Transformer Cost and Life Expectancy
23. How does the cost of a buck-boost transformer compare to that of
an insulating transformer — both capable of handling the same load?
For the most common buck-boost applications, the dollar savings are
generally greater than 75% compared to the
use of an insulating type distribution transformer for the same
application. 24. What is the life expectancy of a buck boost transformer?
The life expectancy of a buck-boost transformer is the same as the life
expectancy of other dry type transformers.
25 What is the definition of an autotransformer and how does it
differ from an isolation transformer?
An autotransformer is a transformer in which the primary (input) and the
secondary (output) are electrically connected to each other. An
isolation transformer, also known as an insulating transformer, has
complete electrical separation between the primary (input) and the
secondary (output). An autotransformer changes or transforms only
a portion of the electrical energy it transmits. The rest of the
electrical energy flows directly through the electrical connections
between the primary and secondary. An isolation transformer
(insulating transformer) changes or transforms all of the electrical
energy it transmits. Consequently, an autotransformer is smaller,
lighter in weight, and less costly than a comparable KVA size insulating
transformer. Buck-boost transformers are frequently field-connected as
autotransformers. 26. Buck-boost transformers are almost always installed as
auto-transformers. Does the N.E.C. (National Electrical Code) permit the
use of autotransformers?
Yes. Please refer to N.E.C. Article 450-4, “Autotransformers 600 Volts,
Nominal, or Less.” Item (a) explains how to over current protect an
autotransformer; item (b) explains that an insulating transformer such
as a buck-boost transformer may be field connected as an
autotransformer. 27. When a buck-boost transformer is connected as an autotransformer
such as boosting 208V to 230V, the KVA is greatly increased. What is the
procedure for determining the size (ampere rating) of the overcurrent
protective device such as a fuse or circuit breaker?
The National Electrical Code Article 450-4 addresses over current
protection of autotransformers. A copy is reproduced below for easy
450-4. Autotransformers 600 Volts, Nominal, or Less. (a) Overcurrent
Protection. Each autotransformer 600 volts,
nominal, or less shall be protected by an individual overcurrent device
installed in series with each ungrounded input conductor. Such
overcurrent device shall be rated or set at not more than 125 percent of
the rated full-load input current of the autotransformer. An overcurrent
device shall not be installed in series with the shunt winding (the
winding common to both the input and the output circuits) of the
autotransformer between Points A and B as shown in Diagram 450-4.
Exception: Where the rated input current of an autotransformer is 9
amperes or more and 125 percent of this current does not correspond to a
standard rating of a fuse or non-adjustable circuit breaker, the next
higher standard rating described in Section 240-6 shall be permitted.
When the rated input current is less than 9 amperes, an overcurrent
device rated or set at not more than 167 percent of the input current
shall be permitted.
(b) Transformer Field-Connected as an Autotransformer. A transformer
field-connected as an autotransformer shall be identified for use at
28. I have noted the reprint of the N.E.C. (National Electrical
Code), Article 450-4 shown in the previous question covering
autotransformer overcurrent protection. Could you explain this article
in detail by citing an example?
An example of an everyday application is always a good way to explain
the intent of the “Code.” Example: A 1 KVA transformer Catalog No.
T-1-11683 has a primary of 120 x 240V and a secondary of12 x24V. It is
to be connected as an autotransformer at the time of installation to
raise 208V to 230V single phase. When this 1 KVA unit is connected as an
autotransformer for this voltage combination, its KVA rating is
increased to 9.58 KVA
(may also be expressed as 9,580 VA). This is the rating to be used for
determining the full load input amps and the sizing of the overcurrent
protect device (fuse or breaker) on the input.
Full Load Input Amps = 9,580 Volt Amps = 46 Amps
When the full load current is greater than 9 amps, the overcurrent
protective device (usually a fuse or non-adjustable breaker) amp rating
can be up to 125 percent of the full load rating of the autotransformer
Max. amp rating of the overcurrent device
= 46 amps x 125% = 57.5 amps
The National Electrical Code, Article 450-4 (a) Exception, permits the
use of the next higher standard ampere rating of the overcurrent device.
This is shown in Article 240-6 of the N.E.C. Max. size of the fuse or
= 60 amps
Steps for Selecting the Proper Buck-Boost Transformer
You should have the following information before selecting a buck-boost
transformer. Line Voltage — The voltage that you want to buck (decrease) or
boost (increase). This can be found by measuring the supply line voltage
with a voltmeter. Load Voltage — The voltage at which your equipment is designed to
operate. This is listed on the nameplate of the load equipment. Load KVA or Load Amps — You do not need to know both —one or the
other is sufficient for selection purposes. This information usually can
be found on the nameplate of the equipment that you want to operate. Frequency — The supply line frequency must be the same as the
frequency of the equipment to be operated — either 50 or 60 cycles. Phase — The supply line should be the same as the equipment to be
operated — either single or three phase.
120 X 240 PRIMARY VOLTS-12/24 SECONDARY VOLTS-60Hz
120 X 240 PRIMARY VOLTS-16/32 SECONDARY VOLTS-60Hz
240 X 480 PRIMARY VOLTS-24/48 SECONDARY VOLTS-60Hz
allows signal or power to be taken from one device and fed into
another without electrically connecting the two.
are devices that transfer electrical energy from one electric
circuit to another, without changing the frequency, by
are designed to meet certain performance specifications and size
requirement that you require. There is a wide range of custom
Buck Boost Transformers
is a ideal solution for changing line voltage by small amounts.
Often used to buck (lower), or boost (raise) the voltage from 208v
to 240v for lighting applications.
Pole Mounted Transformers
are mounted to poles for overhead electrical lines. Used in various applications.
Are available in single phase or three phase transformers.
Medium Voltage Transformers
are used with a medium range of voltages. They come in a full
range from liquid-filled, convention dry type as well as cast coil.
Pad Mounted Transformers
are a excellent choice for commercial and industrial such as
manufacturing facilities, refineries, office buildings, schools,
hospitals, restaurants, and retail stores. They come in various
sizes and can be used underground as well.
typically these voltage transformers are used in power transmission
applications. High voltage transformers are also used in microwave.
- With Acme Electric being in business
over 80 years, they have always believed in offering there customers superior service, quality and technical expertise in the
AMVECO Transformers -
AMVECO designs and manufactures toroids
transformers, current transformers, and auto transformers. Most
AMVECO products are custom designed utilizing their state-of-art proprietary
CAD programs. The AMVECO engineers can quickly generate designs in a
matter of hours, if needed.
Federal Pacific Transformers -
Federal Pacific is a division of Electro- Mechanical Corporation, a
privately held, American owned company founded in 1958. Federal
pacific offers dry-type transformers from .050 KVA through 10,000
KVA single and three phase, up to 34.5 KV, 150 KV BIL with UL
approval through 15 KV.
Marcus Transformer - Ever since they opened their doors for business a half a century ago,
they have been a leader in innovative transformer design. As a
family-owned company they are proud of the reputation they have
earned for making quality-built transformers that deliver
exceptional performance and savings.
Hammond Transformers - Hammond Manufacturing was founded in 1917 in Guelph, Ontario,
Canada. In the last 3 decades it has expanded to the US and the
international markets offering many types of power transformers.
- TEMCo Transformer, a family-owned business which has been
manufacturing and distributing electrical products since
1968. They focus on transformers that significantly
reduce power consumption over 30 percent compared to competitive
GE Transformers - GE has been a key player in the energy industry for
more than a century. Since the installation of
their first steam turbine in 1901. They have become
number one provider of high-technology power generation
and distribution equipment.
Jefferson Electric Transformers - Jefferson Electric has
been a pioneer and innovator of magnetic products since 1915.
Jefferson broad line of dry-type transformers are backed by quality
assurance systems so stringent that each and every unit gets
thoroughly tested before it goes out there door.
Distribution Transformers - Distribution
transformers are generally used in electrical power
distribution and transmission power. This class of transformer has
the highest power, or volt-ampere ratings. and the highest
continuous voltage rating.
Substation Transformers - Substation Transformers are large
devices which usually weigh tens of thousands of pounds. They are
filled with tens of thousands of gallons of heat transfer fluid.
Although they are typically 99.8% efficient in the transforming of
electricity from one voltage to another, processing hundreds of Mega
Volts-Amps of electricity force the liberation of hundreds of BTUs
Medical Grade Isolation Transformer -
Medical Grade Transformers generally refer to the transformers
used in medical devices as well as hospital, biomedical and patient
care equipment. There are a number of strict safety rules,
guidelines and laws governing the design, construction and the test
of these transformers.
Drive Isolation Transformer -
They are used to isolate a drive from a main power line to
prevent the transmission of harmonics that the drives produce back
into the power line. They stop drive harmonics from disrupting
computers and other sensitive equipment.
Toroidal Transformers -
Toroidal Transformers are more efficient than the cheaper laminated EI types of similar power level. Some of the advantages are smaller
size, lower weight, less mechanical hum, (making them superior in
audio amplifier), low-off-load loss.
Step-Up Transformers - A Step-Up Transformer is one whose
secondary voltage is greater than its primary voltage.
This kind of transformer "steps up" the voltage applied
to it. -
- A Step-Down Transformer is designed to reduce voltage from primary to
They can range from sizes from .05 KVA to 500 KVA
Isolation Transformers -
An Isolation Transformer is a device that transfers energy from
the alternating current (AC) supply to an electrical or electronic
load. It isolates the windings to prevent transmitting certain
types of harmonics.
Buck Boost Transformers - Buck Boost
Transformers make small adjustments to the incoming voltage. They
are often used to change voltage from 208v to 240v for lighting
applications. Major advantages of Buck boost transformers
include; low cost, compact size and light weight.
High Voltage Transformer - There are many different types of
voltage transformers. A High Voltage Transformer operates with high
voltages. Typically, these voltage transformers are used in power
transmission applications, where voltages are high enough to present
a safety hazard.
Medium Voltage Transformers -
A Medium Voltage Transformer can be connected directly to a primary
distribution circuit and generally has the most load diversity.
These voltage transformers have installation practices that are
generally in accordance with application recommendations from the
Institute of Electrical and Electronic Engineers (IEEE).
Low Voltage Transformers
- A Low Voltage Transformer is an electrical device that transforms
120 volts (line voltage) into 12 volts or 24 volts (low voltage).
Some uses for low voltage transformer are in landscaping lighting.
Single Phase Transformers - In electrical engineering, single-phase electric power refers to the
distribution of electric power using a system in which all the
voltages of the supply vary in unison. Single-phase distribution is
used when loads are mostly lighting and heating, with few large
Three Phase Transformers - Three
Phase Transformers must have 3 coils or windings connected in
the proper sequence in order to match the incoming power and
therefore transform the power company voltage to the level of
voltage needed while maintaining the proper phasing or polarity.
Custom Transformers -
Custom Transformers are designed for a certain performance
specifications and size requirements. The company works with
your engineering specification.
Industrial Control Transformers -
Industrial Control Transformers are used to convert the
available supply voltage to the required voltage to supply
industrial control circuits and motor control loads.
Pad Mounted Transformers - Pad
Mounted Transformers are usually single phase, or three phase, and
used where safety is a main concern. Typical applications;
restaurant, commercial building, shopping mall, institutional.
Pole Mounted Transformers -
Pole Mounted Transformers are used for distribution in areas
with overhead primary lines. Outside a typical house one can see one
of these devices mounted on the top of an electrical pole.
Oil Filled Transformers -
Oil Filled Transformers are transformers that use insulating oil as
insulating materials. The oil helps cool the transformer.
Because it also provides part of the electrical insulation between
internal live parts, transformer oil must remain stable at high
temperatures over an extended period.
Dry Type Transformers - Dry-Type
Transformers are available for voltages up through 34.5 kV
(although the most common upper limit is 15) and KVA ratings up
through 10,000 (with 5000 as the usual limit). Dry-type use air as a
coolant, lowering health and environmentally concerns.
Auto Transformers -
An Autotransformer is an electrical transformer with only one
winding. The winding has at least three electrical connection points
called taps. Autotransformers are frequently used in power
applications to interconnect systems operating at different voltage
classes, for example 138 kV to 66 kV for transmission. Another
application is in industry to adapt machinery built for 480 V
supplies to operate on the local 600 V supply.
Electrical Transformers are devices used to raise or lower the
voltage of alternating current. For instance, power is transported
over long distance in high voltage power lines and then transformers
lower the voltage so that the power can be used by a business or household.
An Isolating Transformer is a transformer, often with
symmetrical windings, which is used to decouple two circuits.
An Isolation transformer allows an AC signal or power to be taken
from one device and fed into another without electrically connecting
the two circuits. Isolation transformers block transmission of DC
signals from one circuit to the other, but allow AC signals to pass.
Power Lines - A Transmission Line is the material medium or structure that forms
all or part of a path from one place to another for directing the
transmission of energy, such as electromagneticor acoustic waves as well as electric power
transmission. Components of transmission lines include wires, coaxialcables, dielectric slabs, option fibers,electric power lines, and waveguides.
Transformer Voltage - The measure of the amount of force on a
unit charge because of the surrounding charge.
Transformer Frequency -
The transformer cannot change the frequency of the supply. If the
supply is 60 hertz, the output will also be 60 hertz.
Transformer K Factor - Some transformers are now being offered
with a k-factor rating. This measure the transformer's ability to
withstand the heating effects of non-sinusoidal harmonic currents
produced by much of today's electronic equipment and certain
Primary Voltage - The coil winding that is directly connected
to the input power.
Harmonic Cancellation -
Harmonic cancellation is performed with harmonic canceling
transformers also known as phase-shifting transformers. A harmonic
canceling transformer is a relatively new power quality product for
mitigating harmonic problems in electrical distribution systems.
This type of transformer has patented built-in electromagnetic
technology designed to remove high neutral current and the most
harmful harmonics from the 3rd through 21st.
Enclosed transformers come with a weatherproof standard set by
Epoxy Encapsulated -
A process in which a transformer or one of its components is
completely sealed with epoxy or a similar material. This process is
normally preferred when a unit might encounter harsh environmental
Voltage Regulators - A
Voltage Regulator is an electrical regulator designed to
automatically maintain a constant voltage level.
It may use an electromechanical mechanism, or passive or active
electronic components. Depending on the design, it may be used to
regulate one or more AC or DC voltages.
AC Line Reactor -
AC Line Reactors is a three phase transformer used in
conjunction with AC variable frequency and DC motor drive.
They are a bi-directional protective filtering device.
Line Power Conditioners -
Power or Line Conditioners regulate, filter, and suppress noise in
AC power for sensitive computer and other solid state equipment.
DC Power Supplies -
Conversion of one form of electrical power to another desired
form and voltage. This typically involves converting 120 or 240 volt
AC supplied by a utility company to a well-regulated
lower voltage DC for electronic devices.
Rotary Phase Converters -
Rotary Phase Converters are commonly used in home or small
commercial or industrial settings. Rotary phase converters convert
single-phase power into three-phase power. This is a very
cost-effective way to power three-phase electric motors and other
three phase equipment.
Frequency Converters -
A Frequency Changer or Frequency Converter is an
electronic device that converts alternating current (AC) of one
frequency to alternating current of another frequency.
Voltage Converters -
A Voltage Converter changes the voltage of an electrical power
source and is usually combined with other components to create a
Magnetic Motor Starters - Magnetic Motor Starters are
essentially heavy duty relays mounted in boxes, often equipped with
heater/thermal overloads matched to the motor they start.
Motor Starting Auto Transformers - An Auto
Transformer starter uses an auto transformer to reduce
the voltage applied to a motor during start. The auto transformer
may have a number of output taps and be set-up to provide a single
stage starter, or a multistage starter.