passing through a metal enclosure, such as a current path through the tank wall. The inside of the bushing may contain paper insulation and the bushing is often filled with oil to provide additional insulation. The main failure mode of the bushing is short circuit. A short circuit in the bushing can either happen due to material faults in the isolation or due to damage. A damage on bushings of porcelain can occur due to earthquakes or sabotage, like stone throwing. A damage can also occur during handling, shipping or due to flying parts from other failed equipment. A material fault in the isolation can occur due to water or dirt. Damages, cracks in the porcelain and bad gaskets can give water an entrance to the oil isolation in the bushing.