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 comply with NEC Article 210-9, Exception 1, when field connected as an autotransformer. GE bucking and boosting transformers provide an economical and convenient means for bucking or boosting voltage, usually no more than +/-20% on single and three phase circuits. They are compact, relatively light in weight and can be easily installed for indoor or outdoor service.