The paper describes an intercomparison of measuring systems for current transformers accuracy testing between three laboratories Koncar -Instrument Transformers, Koncar -Electrical Engineering Institute and Electrical Engineering Institute Nikola Tesla. All laboratories are accredited according to EN/ IEC 17025: 2017 standard. The obtained discrepancies in ratio and phase errors are within participant's declared measurement uncertainties. All laboratories have confirmed their competence (|E n |≤1) for the applied measurement methods, in accordance with EN ISO/ IEC 17043.