Buck Boost Transformers Sizing Calculator with Buck Boost Transformer Wiring Diagram

What is a Buck Boost Transformer?

Buck-Boost Transformers are small single phase isolation transformers that will reduce (Buck) or raise (Boost) line voltage when connected as an Autotransformer. The most common application is Boosting 208 to 230V. Two or three may be banked for three phase application where the neutral is available from the input. Much smaller transformers may be used in Buck-Boost applications, since the size of the transformer is roughly proportional to the change in voltage.
i.e. A 10kVA load at 240V can be increased to 264V, a 10% change can be achieved with a 1kVA transformer.

How to Calculate Buck Boost Transformer Output Voltage

Multiply input voltage by the appropriate number in Voltage Change Table for output voltage.

Voltage Change Table

Reference Diagrams Below for Characteristics
Rating A1 A2 B1 B2
120/240 x 12/24 1.10 0.90 1.20 0.80
120/240 x 16/32 1.13 0.87 1.27 0.77
240/480 x 24/48 1.10 0.90 1.20 0.80
Rating C1 C2 D1 D2
120/240 x 12/24 1.05 0.95 1.10 0.90
120/240 x 16/32 1.07 0.93 1.13 0.87
240/480 x 24/48 1.05 0.95 1.10 0.90

Buck Boost Transformer Sizing Calculator

Multiply load by the appropriate number in Transformer Multiplier Table for approximate transformer size.

Transformer Multiplier Table

Reference Diagrams Below for Characteristics
Rating A1 A2 B1 B2
120/240 X 12/24 0.10 0.11 0.20 0.24
120/240 X 16/32 0.13 0.15 0.27 0.34
240/480 X 24/48 0.10 0.11 0.20 0.24
Rating C1 C2 D1 D2
120/240 X 12/24 0.05 0.05 0.10 0.11
120/240 X 16/32 0.07 0.07 0.13 0.15
240/480 X 24/48 0.05 0.05 0.10 0.11

Boost Transformer Wiring Diagram

A1: Boosting

Transformer A1 Boosting Circuit Diagram

B1: Boosting

Transformer B1 Boosting Circuit Diagram

C1: Boosting

Transformer C1 Boosting Circuit Diagram

D1: Boosting

Transformer D1 Boosting Circuit Diagram

Buck Transformer Wiring Diagram

A2: Bucking

Transformer A2 Bucking Circuit Diagram

B2: Bucking

Transformer B2 Bucking Circuit Diagram

C2: Bucking

Transformer C2 Bucking Circuit Diagram

D2: Bucking

Transformer D2 Bucking Circuit Diagram

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Distribution Transformer

buck boost dry type transformer

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Control Transformer

encapsulated industrial control transformer

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Warning: When using this information to perform electrical work, call a licensed electrician and consult the NEC® for safety. All licensed electricians have passed examinations covering the National Electric Code®, know state and local building codes, and may carry insurance to cover damages