Arc tracking is the process by which a plastic material is transformed from non-conductive to conductive through a process of surface degradation . All three of the following conditions are necessary for arc tracking to occur:
1) A polymeric surface with terminals that have difference in voltage between them (such as a battery case with positive and negative terminals).
2) Contamination leading to completion of an electrical circuit across the polymer surface (such as a salt-water solution from road spray on the battery).
3) Sufficient voltage and time.
Various researchers propose differing theories as to how arc tracking occurs, but all agree that the surface of the polymer may break down to the point of becoming conductive, which can allow a circuit to complete between the terminals. When this occurs, there is a potential for resistance heating of the polymer which can cause ignition.
Testing of direct current (DC) circuits has provided information about the voltages required to generate arc tracking in automotive environments [1, 2, 3]. The following results have been published:
Voltage Results 12 Arc tracking was not observed  24 Potential for arc tracking [2, 3]. 42 Arc tracking was observed for some polymers  60 Arc tracking was observed for all polymers 
It is apparent that arc tracking as an ignition source is unlikely in vehicles with 12 volt systems, possible in 24 volt systems, and of increasing likelihood for systems 42 volts and higher.