Tracking is surface degradation in which leakage current through moisture and dirt causes small dry-band arcs that carbonise or erode organic insulation and leave a conductive trail. Once a track bridges two conductors, flashover or fire follows. It shows up as branching black lines on cable terminations, bushings, circuit boards and plastic housings, and is resisted with high-CTI materials, extra creepage and clean, dry surfaces.
Found tracking across the stress cone, black fern marks right up to the lug, that termination was days from going bang.
Also heard as
- surface tracking
- carbon tracking
Related terms
CTI
Comparative tracking index: voltage an insulating material withstands before tracking under a wet contamination test.
Creepage distance
Shortest route over an insulating surface from one conductive part to another, the dimension that resists tracking.
Partial discharge
Tiny discharge in a void, on a surface or at a sharp edge that never spans the whole insulation, an early sign of decay.
Corona
Faint glowing discharge around high-voltage conductors where the air is overstressed, causing noise and loss.