Dry Type Distribution Transformers
Buck-Boost transformers are small, single phase, dry
type distribution transformers designed and shipped as
insulating/isolating transformers. They have a dual voltage
primary and a dual voltage secondary. These transformers
can be connected for a wide range of voltage combinations.
The most common use is to buck (lower) or boost (raise)
the supply voltage a small amount, usually 5 to 27%.
Buck-boost transformers are in compliance with NEC
Article 210.9, Exception 1 when field connected as
an autotransformer.
The major advantages of Buck-boost transformers are their
low cost, compact size and light weight. They are also more
efficient and cost less than equivalent isolation transformers.
When connected as an autotransformer, they can handle
loads up to 20 times the nameplate rating. A buck-boost
transformer is the ideal solution for changing line voltage by
E77014
small amounts.
When a buck-boost has the primary and secondary windings
Accessories
connected, per recommended instructions, it becomes an
autotransformer. Now, only the secondary windings are
Surge Protective Devices
transforming voltage and current. The majority of the kVA
Active Tracking Filters
load passes directly from the supply to the load. This is the
reason buck-boost transformers can supply a load with a
much larger kVA rating than the nameplate indicates.
Selection Steps
1. Input Line Voltage
Low voltage lighting control applications
Measure the supply voltage with a voltmeter.
SolaHD buck-boost transformers are designed to supply
power to low voltage lighting circuits, control panels or
2. Voltage Required for the Load
other systems requiring 12, 16, 24, 32, or 48 Volts. When
Check the load equipment to determine the voltage
connected as an insulating transformer (by following the
requirement.
wiring diagram located after the specification tables on the
inside of the transformer case), the transformers capacity
3. kVA or Ampere Rating of the Load
matches the nameplate kVA rating.
Find either the load kVA or the load amperage
requirements. This information is listed on the
SolaHD buck-boost transformers are also suited for low
nameplate of the load equipment.
voltage landscape lighting. They are UL Listed for outdoor
service and their compact size makes them the perfect
4. Frequency
solution for providing power to accent lighting applications.
Electrical Connection diagrams are shown at the end of
Either 50 or 60 Hz. The frequency of the transformer
this section.
must match the frequency of the load.
Use dimmers on the output of the transformer that are
5. Number of Phases
designed and rated for use with magnetic loads. We strongly
Single or three phase line and load must match.
recommend contacting the dimmer manufacturer for advice
(A transformer cannot convert single to three phase.)
on your specific lighting application.
A common application is to make a single phase
connection from a three phase supply by using one
Certifications and Compliances
phase of the three phase supply circuit. Be careful not
to overload that phase of the three phase supply. For
Listed
buck-boost applications the supply must provide load
- UL 506
kVA not just the nameplate rating of the buck-boost.
- CSA C22.2 No. 66
Refer to the Selection Tables on the following pages.
Visit our website at www.emerson.com or contact Technical Services at (800) 377-4384 with any questions.
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January 2017Dry Type Distribution Transformers
Three phase, buck-boost applications require two or three
Using the Selection Tables
transformers. Check the Quantity Required column of the
1. Determine if you are trying to Boost (raise) or Buck
Three Phase Selection Tables for the exact quantity.
(lower) your voltage. Select an input/output voltage
combination that comes closest to matching your
Fusing Buck-Boost Transformers
application from the appropriate single or three phase
For determining the correct size of breaker or fuse for a given charts on the following pages.
range of input or output ampere ratings, refer to Section
450.4, of the National Electric Code (NEC). 2. Move across your selected input/output voltage row to
the amperage or kVA rating closest to, but greater than
Where an overcurrent protection device is required, the the rating required by your load.
electrical connections and selection tables will reference
appropriately. 3. Reading the top of the column will give you the
catalog number of the exact buck-boost transformer
you need. See the Specification Tables on the
next page.
4. Connect the transformers according to the diagram
indicated. See the Electrical Connections section at the
end of this section. Connection diagrams are packed
with each transformer.
Overcurrent devices OC-1a and OC-1b are shown correctly installed
in accordance with NEC 450.4. Locating an overcurrent device in series with
the shunt winding anywhere between A and B is not permitted. The shunt
winding is the winding common to both the input and the output circuits.
Visit our website at www.emerson.com or contact Technical Services at (800) 377-4384 with any questions.
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January 2017