Electrical inspection (holiday detection) is a test of the continuity of a protective coating. It detects bubble or blister-type voids, cracks, thin spots, and foreign inclusions or contaminants in the coating that are of such size, number, or conductivity as to lower the electrical resistance or dielectric strength of the coating significantly. Two types of test equipment are used to determine discontinuities: a low voltage wet sponge and a high voltage spark tester. The low voltage wet sponge tester is used to determine discontinuities in coating films having a total film thickness of 20 mils or less. The high voltage spark tester can be used for film thicknesses greater than 20 mils but not restricted to this thickness range.