Power line communication (PLC) is a crucial component of the information and communication technologies within smart grids (SGs). It can use the existing power-grid infrastructure to provide cost-efficient data transmissions. Consequently, PLC has been proposed as a key technology to support different SG applications. However, its performance gain might be degraded in the presence of channel attenuation and high unpredictable noise levels. In this study, we evaluated the performance of a narrow-band (NB)-PLC system, and we derived the corresponding successful transmission probability (STP). In addition, field measurements were conducted and the data used to confirm the derived STP expression and to assess the NB-PLC system performance. The theoretical and field measurement results show the dependency of PLC system performance on the selected channel and the transmission environment parameters.