The right voltage ratio for a miniature voltage transformer is the ratio that scales the real primary voltage into the intended input range of the meter or control device, while still maintaining the needed accuracy under the actual burden and wiring scheme. In practice, that means buyers should check five things together: system voltage, target secondary voltage, burden level, device configuration method, and insulation context. When those five line up, ratio selection becomes straightforward. When they do not, even a technically “correct” ratio can become the wrong purchasing decision.