In the event of potential differences between two adjacent tracks of a printed circuit board or between two plug contacts, an electric field builds up which can cause a current flow, the leakage current, across the insulating material lying between the tracks.
The amount of leakage current depends on the distance between the traces, moisture, contamination and other external influences on the PCB material. Since the electric field causes a more or less small current flow that slowly builds up between the live conductors across the insulating material, it is referred to as leakage current.
Iolier strength is a measure of tracking current strength, Comparative TrackingIndex( CTI). It depends on the water absorption capacity of the insulating material and the spacing of the live conductors. The CTI value is a dimensionless value determined in a precisely defined test procedure according to IEC 60112. CTI values range from 125 for phenolic resin to 600 for polytetrafluoroethylene(PTFE). The tracking resistance and the required conductor spacing are specified in the VDE regulations VDE 0110 and VDE 030/1.