# 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

## Buck Transformer Wiring Diagram

### Shop Transformers

#### Control Transformer

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