Creepage and Clearance Distances in Electrical Equipment for Shipboard Use

The influence of a number of ionic liquid contaminants and of some oils upon the tracking behavior of three typical insulants, (phenolic-bonded paper board, cellulose-filled alkyd molding and glass-filled polyester dough molding compound), is measured in terms of electrode separation (creepage) and resistance to tracking as determined by the wet contamination test of IEC 112. For any one contaminant the IEC test predicts the correct order of the tracking resistance of the insulants, but the effects of different contaminants is not consistent between materials. Increasing the electrode separation seldom produces a prorata increase in the time required to track insulation, whereas using a higher CTI material will always reduce the chance of tracking. The influence of contamination upon flashover distance (clearance) is shown to be small.