The autotransformer: for step-up, step down and split phase balancing. An autotransformer can be used for step-up, step-down and split phase output balancing purposes. While the step-up and step-down functions are fairly straightforward, split phase output balancing may require some more attention. Consider for example a 30A 120/240V split phase supply. The supply could be the grid, a generator or two stacked inverters. Some of the loads connected are 240V, others are 120V. On each 120V leg the load should not exceed 30A. The problem is that as soon as 120V loads are connected, the two legs will show a different current. This is because the 120V loads on the two legs will never be balanced. The solution is an autotransformer.