The admittance summation method is efficient in short circuit analysis of radial and weakly meshed networks. It is especially powerful if all node loads can be represented as any combination of constant impedance and constant current load component. However, in the existing literature one cannot find any explanation how to handle power transformer in that approach. For that reason, the corresponding equations have been developed in this paper along with a procedure for development of a three-winding transformer admittance matrix. In addition, a procedure for handling an arbitrary load was proposed. A large number of tests were performed and results were compared with that obtained by the previously published method. As an illustration, some of the results for single fault currents are presented. It can be concluded that the proposed approach makes the admittance summation method capable to take into account all network elements in a proper way.