International instrument transformer standardization efforts include alternative designs in their scope. Easy-to-use Rogowski coils fall within the so-called “low power passive current transformers” category. The ART overcomes the main disadvantage of split-core Rogowski coils by adding a simple ferrite core at the clasp. This leads to a near perfect independence of the ratio error on the position of the primary conductor. A well-characterized winding support ensures an absolute error low enough to be acceptable for billing purposes.