The purpose of this study was to identify a method to form rubber composites by incorporating natural rubber (NR) and wood ash from rubber trees with a preliminary electrical properties test. This formulation is intended to improve the rubber composites in order to obtain new materials for high voltage insulators. First, the rubber formulation and processing conditions were optimised before the composites are processed in the laboratory. Second, the interactions between the NR and wood ash were investigated with the following tests: cure time, agglomerate dispersion, SEM images, and the electrical characteristic test. In the electrical characteristic test, the experimental setup was designed for testing the frequency range from 50 Hz to 100 kHz, which is the range of high voltage power line switching frequencies. This energised transient frequency can occur due to switching operations or any other external causes in high voltage systems. Finally, the dielectric property of the rubber composites was evaluated and the equivalent circuit was formulated. The results show that the different properties tested with the new material not only correspond with the filler contents, but also with the frequencies in the transmission lines. The measured data are extracted and converted into other parameters at each frequency. The comparison results are closely matched. Moreover, the results revealed that relative permittivity and the conductivity increases the wood ash filler is increased.