In this paper, full rate space-time-frequency coding applied to orthogonal frequency division multiplexing based power line communication systems. The proposed systems yield both time and frequency diversity and keep transmission rate full. Performances of the systems are evaluated for three conductors of low voltage indoor cables and are compared with space-frequency and space-time-frequency coding applied power line communication systems in the literature. Owing to the higher order diversity level the proposed full rate space-time-frequency systems have an increasing advantage over space-frequency systems as the SNR level above 12.5 dB. On the other hand, owing to transmission rate advantage, the proposed full rate space-time-frequency systems can have more than 6 dB gain over the other space-time-frequency coding applied power line communication systems in the literature.