Extends the ratio range of a Megger 550005B Single-Phase Hand-Cranked Transformer Turns Ratio (TTR) Test Set (sold separately). The transformer extends the range of the TTR to 329.99:1 and includes all cords needed to connect it to the 550005B. The 550030 is used with the 550005B to test single-phase power, potential, and current transformers by electricians and electrical contractors.