Unlike the voltage transformer, a current transformer measures current from one circuit to another, which requires different calculations to create the optimal design.

As noted above, basic point-to-point fault current calculations are derived using Ohm's Law. System characteristics like voltage, conductor length, conductor constants, available short circuit values ...

The equation can be used to calculate what the output voltage might be from a particular transformer, or to work out how to design a transformer to make a particular voltage change.