Major advantages of buck-boost transformers include compact size, light weight and suitability for outdoor use. They are also more efficient and cost less than equivalent isolation transformers.
When a buck-boost transformer has the primary and secondary windings connected according to the recommended instructions, it becomes an autotransformer. In this configuration, only the secondary windings transform voltage and current. The majority of the kVA load passes directly from the supply to the load. This allows buck-boost transformers to handle kVA loads up to 20 times the nameplate rating. Buck-boost transformers comply with NEC Article 210-9, Exception 1 when field connected as an autotransformer.