The relation among the common-mode current generated by PLC system, the longitudinal conversion loss (LCL) and the common-mode impedance (Zcm) of the T-ISN and the electrical unbalance that exists in the PLC device is investigated in order to realize a low emission PLC device. It is necessary to decrease the common-mode current to reduce the radiated emission generated from PLC system. In this case, the LCL and the common-mode impedance of the outlet are examined. For this examination, the formula of the common-mode current, the LCL, and the common-mode impedance is obtained. First of all, the relation among the common-mode current, the LCL and the common-mode impedance is shown. Next, the influence of the electrical balancing of the PLC device on the common-mode current reduction is shown. The effectiveness of the improvement of balancing by means of the components layout and the wirings of the PLC device is shown.