Abstract: Three-phase transformer testing method and system enabling convenient performance of ANSI-required checking of polarity and phase-relation and also enabling measurements of core loss, load loss and transformer ratio to be performed conveniently. Only a total of six test leads are needed, being connected one each to three high-voltage transformer terminals H1, H2 and H3 and being connected one each to three low-voltage terminals X1, X2 and X3. Since only six test leads are needed, it is easy to arrange them and to connect them without confusion to the six transformer terminals.