This paper studies the electrical properties of ternary Graphite (Gr)/Multi-Walled Carbon Nanotube (MWCNT)/polyester (PS) composites and binary Gr/PS composites, focusing on how charge concentrations affect the conductivity. Conductivity increases sharply at the percolation threshold, forming a conductive network in the polyester matrix. Both series of studied samples reach the percolation threshold at 0.2 wt% MWCNT. Series 1, with lower graphite content, shows a significant conductivity increase with MWCNT addition, whereas Series 2, with higher graphite content, maintains higher conductivity overall. The study explores AC and DC conductivity, revealing Positive Temperature Coefficient in Resistivity (PTCR) and Negative Temperature Coefficient in Resistivity (NTCR) effects. The PTCR effect, marked by reduced conductivity with increasing temperature, is stronger in high-graphite composites due to disrupted pathways from thermal expansion. In contrast, the NTCR effect indicates enhanced charge mobility at higher temperatures. Series 2 displays more prominent PTCR/NTCR effects and higher activation energies, suggesting more complex conduction mechanisms compared to the more homogeneous activation energies of Series 1.