Tracking is a phenomenon in Electrical Insulation. Tracking refers to the flow of current over the surface of the insulation. Tracking causes heating which results in damage to the insulation. As current gets a path to the ground or another energized conductor, tracking can lead to a flash over.
Tracking is caused by many factors. One principal reason is dust. Dust forms a layer over the insulation, this when combined with moisture in the atmosphere provides a conductive layer for the current to flow. Other factors which can cause tracking are humidity which can cause condensation, temperature, air pressure, etc.
Tracking can be prevented by ensuring proper creepage distance. Equipment should be kept at the right temperature and humidity.