Abstract: This study focuses on the risk of cable single-phase grounding faults in 10-kilovolt distribution networks causing arc ignition of the cables and triggering tunnel fires. An experimental platform was constructed to investigate the ignition characteristics of 4A, 6A, 8A, and 10A small current fault arcs on the cables. The experiment revealed that the cable insulation material (XLPE) is highly susceptible to ignition, with the ignition time being extremely short (0.03-0.04 seconds). As the arc current increases, the maximum temperature, mass loss, and ignition loss of the cable also increase. When the current exceeds 6A, the flame spreads from a single direction to both ends. Based on the experimental results, the FDS software was used to establish an equivalent heat source model through an inversion method to simulate the arc ignition process. This model was applied to the simulation of the cable tunnel scenario to analyze the damage caused by the fault arc to adjacent cables. The simulation results show that the temperature of the outer sheath (PVC material) of the adjacent cable directly above the fault point significantly increases. At currents of 6A and above, the temperature exceeds 200°C, which has reached the decomposition temperature of PVC, causing damage to the cable; while at 4A current, the temperature is 182°C, causing only softening.