This paper quantifies experimentally the impact of ten parameters on transformer excitation current. These parameters belong to the following six categories: (1) annealing process, (2) mechanical process, (3) operating conditions, (4) magnetic material, (5) assembly process, and (6) core design process parameters. The conclusions of this research are very useful during both the design and production phases of transformers. Consequently, transformers can be designed and manufactured to fulfill the excitation current specifications.